View source for Obesity

{{Short description|Medical condition of excess body fat}}
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{{about|the condition of animals|the journal|Obesity (journal){{!}}''Obesity'' (journal)}}
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{{Infobox medical condition (new)
| name          = Obesity
| image         = File:FatCT2008 (cropped).JPG
| alt           = 
| caption       = Abdominal [[computed tomography]] of an obese person showing excess abdominal adiposity
| field         = [[Endocrinology]], [[bariatrics]]
| symptoms      = Increased fat<ref name=WHO2015/>
| complications = [[Cardiovascular disease]]s, [[type 2 diabetes]], [[obstructive sleep apnea]], certain types of [[cancer]], [[osteoarthritis]], [[Depression (mood)|depression]]<ref name=HaslamJames/><ref name=Luppino2010rev/>
| onset         =
| duration      =
| types         =
| causes        = Excessive consumption of energy-dense foods, sedentary work and lifestyles and lack of physical activity, changes in modes of transportation, urbanization, lack of supportive policies, lack of access to a healthy diet, genetics<ref name=WHO2015/><ref name=Yaz2015/>
| risks         =
| diagnosis     = [[Body mass index|BMI]] > {{val|30|ul=kg/m2}}<ref name=WHO2015/>
| differential  =
| prevention    = Societal changes, changes in the food industry, access to a healthy lifestyle, personal choices<ref name=WHO2015/>
| treatment     = Diet, exercise, medications, surgery<ref name=Yan2014/><ref name=Col2014/>
| medication    =
| prognosis     = Reduced [[life expectancy]]<ref name=HaslamJames/>
| frequency     = Over 1 billion / 12.5% (2022)<ref name="Worldwide trends">{{cite journal |last1=NCD Risk Factor Collaboration |title=Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults |journal=The Lancet |date=February 29, 2024 |volume=403 |issue=10431 |pages=1027–1050 |doi=10.1016/S0140-6736(23)02750-2|pmid=38432237 |pmc=7615769  |issn = 0140-6736 }}</ref>
| deaths        = 2.8 million people per year
}}
{{Human body weight}}

<!-- Definition and symptoms -->
'''Obesity''' is a medical condition, considered by multiple organizations to be a [[disease]],<ref>{{cite journal | vauthors = Powell-Wiley TM, Poirier P, Burke LE, Després JP, Gordon-Larsen P, Lavie CJ, Lear SA, Ndumele CE, Neeland IJ, Sanders P, St-Onge MP | title = Obesity and Cardiovascular Disease: A Scientific Statement From the American Heart Association | journal = Circulation | volume = 143 | issue = 21 | pages = e984–e1010 | date = May 2021 | pmid = 33882682 | pmc = 8493650 | doi = 10.1161/CIR.0000000000000973 }}</ref><ref>{{Cite web |last=CDC |date=21 March 2022 |title=Causes and Consequences of Childhood Obesity |url=https://www.cdc.gov/obesity/basics/causes.html |access-date=18 August 2022 |website=Centers for Disease Control and Prevention |language=en-us |archive-url=https://web.archive.org/web/20220415155258/https://www.cdc.gov/obesity/basics/causes.html |archive-date=15 April 2022}}</ref><ref>{{Cite web |title=Policy Finder |url=https://policysearch.ama-assn.org/policyfinder/detail/obesity?uri=/AMADoc/HOD.xml-0-3858.xml |access-date=18 August 2022 | work = American Medical Association (AMA) }}</ref> in which excess [[Adipose tissue|body fat]] has accumulated to such an extent that it can have negative effects on [[health]]. People are classified as obese when their [[body mass index]] (BMI)—a person's weight divided by the square of the person's height—is over {{val|30|ul=kg/m2}}; the range {{val|25|–|30|ul=kg/m2}} is defined as [[overweight]].<ref name=WHO2015/> Some [[East Asia]]n countries use lower values to calculate obesity.<ref name="Kan2005">{{Cite book |title=Nutrition and Fitness: Obesity, the Metabolic Syndrome, Cardiovascular Disease, and Cancer |vauthors=Kanazawa M, Yoshiike N, Osaka T, Numba Y, Zimmet P, Inoue S |date=2005 |isbn=978-3-8055-7944-5 |series=World Review of Nutrition and Dietetics |volume=94 |pages=1–12 |chapter=Criteria and Classification of Obesity in Japan and Asia-Oceania |doi=10.1159/000088200 |pmid=16145245 |s2cid=19963495 }}</ref> Obesity is a major cause of disability and is [[Obesity-associated morbidity|correlated with various diseases and conditions]], particularly [[cardiovascular disease]]s, [[type 2 diabetes]], [[obstructive sleep apnea]], certain types of [[cancer]], and [[osteoarthritis]].<ref name="HaslamJames">{{cite journal | vauthors = Haslam DW, James WP | title = Obesity | journal = Lancet | volume = 366 | issue = 9492 | pages = 1197–1209 | date = October 2005 | pmid = 16198769 | doi = 10.1016/S0140-6736(05)67483-1 | type = Review | s2cid = 208791491 }}</ref><ref name=":2">{{Cite web|title=Obesity - Symptoms and causes |url=https://www.mayoclinic.org/diseases-conditions/obesity/symptoms-causes/syc-20375742 |access-date=30 November 2021|website=Mayo Clinic|language=en}}</ref><ref name=":0" />

<!-- Causes, Prevention & Treatment -->
Obesity has individual, socioeconomic, and environmental causes. Some known causes are [[Western pattern diet|diet]], low physical activity, [[automation]], [[urbanization]], [[genetic susceptibility]], [[medications]], [[mental disorder]]s, [[economic policies]], [[endocrine disorder]]s, and exposure to [[endocrine-disrupting chemicals]].<ref name=WHO2015/><ref name="Yaz2015">{{cite journal | vauthors = Yazdi FT, Clee SM, Meyre D | title = Obesity genetics in mouse and human: back and forth, and back again | journal = PeerJ | volume = 3 | article-number = e856 | date = 2015 | pmid = 25825681 | pmc = 4375971 | doi = 10.7717/peerj.856 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Kassotis CD, Vandenberg LN, Demeneix BA, Porta M, Slama R, Trasande L | title = Endocrine-disrupting chemicals: economic, regulatory, and policy implications | journal = The Lancet. Diabetes & Endocrinology | volume = 8 | issue = 8 | pages = 719–730 | date = August 2020 | pmid = 32707119 | pmc = 7437819 | doi = 10.1016/S2213-8587(20)30128-5 }}</ref><ref name="Ble2008">{{cite journal | vauthors = Bleich S, Cutler D, Murray C, Adams A | title = Why is the developed world obese? | journal = Annual Review of Public Health | volume = 29 | pages = 273–295 | year = 2008 | pmid = 18173389 | doi = 10.1146/annurev.publhealth.29.020907.090954 | doi-access = free | type = Research Support }}</ref>

<!--Treatment & Prevention-->
While many people with obesity attempt to lose weight and are often successful, maintaining weight loss long-term is rare.<ref name=":1">{{cite journal | vauthors = Strohacker K, Carpenter KC, McFarlin BK | title = Consequences of Weight Cycling: An Increase in Disease Risk? | journal = International Journal of Exercise Science | volume = 2 | issue = 3 | pages = 191–201 | date = 15 July 2009 | doi = 10.70252/ASAQ8961 | pmid = 25429313 | pmc = 4241770 }}</ref> Obesity prevention requires a complex approach, including interventions at medical, societal, community, family, and individual levels.<ref name=WHO2015/><ref name=":0"/> Changes to [[diet (nutrition)|diet]] as well as [[physical exercise|exercising]] are the main treatments recommended by health professionals.<ref name=HaslamJames/> Diet quality can be improved by reducing the consumption of energy-dense foods, such as those high in fat or sugars, and by increasing the intake of [[dietary fiber]]. The [[World Health Organization]] stresses that the disease is a societal responsibility and that these dietary choices should be made the most available, affordable, and accessible options.<ref name=WHO2015/> [[Anti-obesity medication|Medications]] can be used, along with a suitable diet, to reduce appetite or decrease fat absorption.<ref name="Yan2014">{{cite journal | vauthors = Yanovski SZ, Yanovski JA | title = Long-term drug treatment for obesity: a systematic and clinical review | journal = JAMA | volume = 311 | issue = 1 | pages = 74–86 | date = January 2014 | pmid = 24231879 | pmc = 3928674 | doi = 10.1001/jama.2013.281361 | type = Review }}</ref> If diet, exercise, and medication are not effective, a [[gastric balloon]] or [[bariatric surgery|surgery]] may be performed to reduce stomach volume or length of the intestines, leading to feeling full earlier, or a reduced ability to absorb nutrients from food. Metabolic surgery promotes weight loss not only by reducing caloric intake but also by inducing sustained changes in the secretion of gut hormones involved in appetite and metabolic regulation.<ref name="Col2014">{{cite journal | vauthors = Colquitt JL, Pickett K, Loveman E, Frampton GK | title = Surgery for weight loss in adults | journal = The Cochrane Database of Systematic Reviews | volume = 2014 | issue = 8 | article-number = CD003641 | date = August 2014 | pmid = 25105982 | pmc = 9028049 | doi = 10.1002/14651858.CD003641.pub4 | type = Meta-analysis, Review }}</ref><ref name="balloon2008">{{cite journal | vauthors = Imaz I, Martínez-Cervell C, García-Alvarez EE, Sendra-Gutiérrez JM, González-Enríquez J | title = Safety and effectiveness of the intragastric balloon for obesity. A meta-analysis | journal = Obesity Surgery | volume = 18 | issue = 7 | pages = 841–846 | date = July 2008 | pmid = 18459025 | doi = 10.1007/s11695-007-9331-8 | s2cid = 10220216 }}</ref>

<!-- Epidemiology, society, and culture -->
Obesity is a leading [[preventable cause of death]] worldwide, with increasing rates in adults and [[childhood obesity|children]].<ref>{{Cite book |url=https://books.google.com/books?id=5aLxBQAAQBAJ&pg=PA158 |title=Encyclopedia of Mental Health |date=2015 |publisher=Academic Press |isbn=978-0-12-397753-3 |edition=2 |page=158}}</ref> In 2022, over 1 billion people lived with obesity worldwide (879 million adults and 159 million children), representing more than a double of adult cases (and four times higher than cases among children) registered in 1990.<ref name="Worldwide trends"/><ref>{{Cite web |title=One in eight people are now living with obesity |url=https://www.who.int/news/item/01-03-2024-one-in-eight-people-are-now-living-with-obesity |access-date=2024-03-01 |website=World Health Organization |date=1 March 2024 |language=en}}</ref> Obesity is more common in women than in men.<ref name="WHO2015">{{Cite web |url=https://www.who.int/mediacentre/factsheets/fs311/en/ |title=Obesity and overweight Fact sheet N°311 |date=January 2015 |website=WHO |access-date=2 February 2016}}</ref> Obesity is [[Social stigma of obesity|stigmatized]] in most of the world. Conversely, some cultures, past and present, have a favorable view of obesity, seeing it as a symbol of wealth and fertility.<ref name=HaslamJames/><ref name="Woodhouse">{{Cite book |title=Obesity in art: a brief overview |vauthors=Woodhouse R |year=2008 |isbn=978-3-8055-8429-6 |series=Frontiers of Hormone Research |volume=36 |pages=271–86 |doi=10.1159/000115370 |pmid=18230908 |url=https://books.google.com/books?id=nXRU4Ea1aMkC&pg=PA271}}</ref> The [[World Health Organization]], the US, Canada, Japan, Portugal, Germany, the [[European Parliament]] and medical societies (such as the [[American Medical Association]]) classify obesity as a disease. Others, such as the [[United Kingdom|UK]], do not.<ref>{{Cite journal|title=The implications of defining obesity as a disease: a report from the Association for the Study of Obesity 2021 annual conference - eClinicalMedicine |journal=eClinicalMedicine |date=2023 |volume=58 |doi=10.1016/j.eclinm.2023.101962 |pmid=37090435 |pmc=10119881 | vauthors = Luli M, Yeo G, Farrell E, Ogden J, Parretti H, Frew E, Bevan S, Brown A, Logue J, Menon V, Isack N, Lean M, McEwan C, Gately P, Williams S, Astbury N, Bryant M, Clare K, Dimitriadis GK, Finlayson G, Heslehurst N, Johnson B, Le Brocq S, Roberts A, McGinley P, Mueller J, O'Kane M, Batterham RL, Miras AD, Miras AD }}</ref><ref name="USGuidelines2013"/><ref name="NYTimes20130618">{{Cite news | vauthors = Pollack A |url= https://www.nytimes.com/2013/06/19/business/ama-recognizes-obesity-as-a-disease.html |title=A.M.A. Recognizes Obesity as a Disease |date=18 June 2013 |work=The New York Times |archive-url=https://web.archive.org/web/20130624124034/http://www.nytimes.com/2013/06/19/business/ama-recognizes-obesity-as-a-disease.html?_r=1& |archive-date=24 June 2013 }}</ref><ref>{{Cite web |url=http://www.hhnmag.com/hhnmag/HHNDaily/HHNDailyDisplay.dhtml?id=5870001020 |title=The Facts About Obesity |vauthors=Weinstock M |date=21 June 2013 |website=H&HN |publisher=[[American Hospital Association]] |access-date=24 June 2013 |archive-date=9 September 2013 |archive-url=https://web.archive.org/web/20130909051439/http://www.hhnmag.com/hhnmag/HHNDaily/HHNDailyDisplay.dhtml?id=5870001020 }}</ref>

==Classification==
{{Main|Classification of obesity}}
{| class="wikitable" style="float: right; margin-left: 1em; text-align:center"
! Category<ref>{{cite book |url=https://apps.who.int/iris/bitstream/handle/10665/43190/9241593024_eng.pdf |title=The SuRF Report 2 |series=The Surveillance of Risk Factors Report Series (SuRF) |page=22 |publisher=World Health Organization |date=2005}}</ref>
! BMI (kg/m<sup>2</sup>)
|-
| style="text-align: left;" | Underweight
| < 18.5
|-
| style="text-align: left;" | Ideal weight
| {{Nowrap|18.5 – 24.9}}
|-
| style="text-align: left;" | Overweight
| 25.0 – 29.9
|-
| style="text-align: left;" | Obese (class I)
| 30.0 – 34.9
|-
| style="text-align: left;" | Obese (class II)
| 35.0 – 39.9
|-
| style="text-align: left;" | Obese (class III)
| ≥ 40.0
|}
[[File:Obesity6.JPG|thumb|upright=1.2|alt=A front and side view of a "class III obese male" torso. Stretch marks of the skin are visible along with gynecomastia.|A "class III obese male" with a BMI of 53&nbsp;kg/m<sup>2</sup>: weight {{cvt|182|kg}}, height {{cvt|185|cm|ftin}}. He presents with [[stretch marks]] and [[Adipomastia|enlarged breasts]].]]
Obesity is typically defined as a substantial accumulation of [[body fat]] that could impact health.<ref name=WHOsheet/> Medical organizations tend to classify people living with obesity as based on [[body mass index]] (BMI) – a ratio of a person's weight in [[kilogram]]s to the [[Square (algebra)|square]] of their height in [[meter]]s. For adults, the [[World Health Organization]] (WHO) defines "[[overweight]]" as a BMI 25 or higher, and "obesity" as a BMI 30 or higher.<ref name=WHOsheet>{{cite web|title=Obesity and overweight |publisher=World Health Organization |date=9 June 2021 |url=https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight |access-date=16 March 2022}}</ref> The U.S. [[Centers for Disease Control and Prevention]] (CDC) further subdivides obesity based on BMI, with a BMI 30 to 35 called class 1 obesity; 35 to 40, class 2 obesity; and 40+, class 3 obesity.<ref>{{cite web|title=Defining Adult Overweight and Obesity |date=7 June 2021 |publisher=U.S. Centers for Disease Control and Prevention |url=https://www.cdc.gov/obesity/adult/defining.html |access-date=16 March 2022}}</ref>

For children, obesity measures take age into consideration along with height and weight. For children aged 5–19, the WHO defines obesity as a BMI two [[standard deviation]]s above the [[median]] for their age (a BMI around 18 for a five-year old; around 30 for a 19-year old).<ref name=WHOsheet/><ref>{{cite web|url=https://www.who.int/toolkits/growth-reference-data-for-5to19-years/indicators/bmi-for-age |access-date=16 March 2022 |title=BMI-for-age (5–19 years) |publisher=World Health Organization}}</ref> For children under five, the WHO defines obesity as a weight three standard deviations above the median for their height.<ref name=WHOsheet/>

Some modifications to the WHO definitions have been made by particular organizations.<ref name=Bei2002/><!-- We describe the organizations that have made modification in the next few sentences --> The surgical literature breaks down class II and III or only class III obesity into further categories whose exact values are still disputed.<ref name=morbid2007>{{cite journal | vauthors = Sturm R | title = Increases in morbid obesity in the USA: 2000–2005 | journal = Public Health | volume = 121 | issue = 7 | pages = 492–6 | date = July 2007 | pmid = 17399752 | pmc = 2864630 | doi = 10.1016/j.puhe.2007.01.006 }}</ref>
* Any BMI ≥ 35 or 40&nbsp;kg/m<sup>2</sup> is ''severe obesity''.
* A BMI of ≥ 35&nbsp;kg/m<sup>2</sup> and experiencing obesity-related health conditions or ≥ 40 or 45&nbsp;kg/m<sup>2</sup> is ''morbid obesity''.
* A BMI of ≥ 45 or 50&nbsp;kg/m<sup>2</sup> is ''super obesity''.

As Asian populations develop negative health consequences at a lower BMI than [[White people|Caucasians]], some nations have redefined obesity; Japan has defined obesity as any BMI greater than 25&nbsp;kg/m<sup>2</sup><ref name=Kan2005/> while China uses a BMI of greater than 28&nbsp;kg/m<sup>2</sup>.<ref name=Bei2002>{{cite journal | vauthors = Bei-Fan Z | title = Predictive values of body mass index and waist circumference for risk factors of certain related diseases in Chinese adults: study on optimal cut-off points of body mass index and waist circumference in Chinese adults | journal = Asia Pac J Clin Nutr | volume = 11 | issue = Suppl 8 | pages = S685–93 | date = December 2002 | doi = 10.1046/j.1440-6047.11.s8.9.x }}; Originally printed as {{cite journal | vauthors = Zhou BF | title = Predictive values of body mass index and waist circumference for risk factors of certain related diseases in Chinese adults--study on optimal cut-off points of body mass index and waist circumference in Chinese adults | journal = Biomedical and Environmental Sciences | volume = 15 | issue = 1 | pages = 83–96 | date = March 2002 | pmid = 12046553 }}</ref>

The preferred obesity metric in scholarly circles is the [[body fat percentage]] (BF%) – the ratio of the total weight of person's fat to his or her body weight, and BMI is viewed merely as a way to approximate BF%.<ref>{{cite journal|url=http://bmb.oxfordjournals.org/content/53/2/238.full.pdf|title=Assessing obesity: classification and epidemiology| vauthors = Seidell JC, Flegal KM |journal=British Medical Bulletin|year=1997|volume=53 |issue=2 |pages=238–252 |doi=10.1093/oxfordjournals.bmb.a011611 |pmid=9246834 }}</ref> According to ''American Society of Bariatric Physicians'', levels in excess of 32% for women and 25% for men are generally considered to indicate obesity.<ref>{{Cite journal |last1=Lin |first1=Ting-Yun |last2=Lim |first2=Paik-Seong |last3=Hung |first3=Szu-Chun |date=2017-12-23 |title=Impact of Misclassification of Obesity by Body Mass Index on Mortality in Patients With CKD |journal=Kidney International Reports |volume=3 |issue=2 |pages=447–455 |doi=10.1016/j.ekir.2017.12.009 |issn=2468-0249 |pmc=5932305 |pmid=29725649}}</ref>

BMI is now viewed as outdated in some countries because it ignores variations between individuals in amounts of [[lean body mass]], particularly [[muscle]] mass. Individuals involved in heavy physical labor or sports may have high BMI values despite having little fat. For example, more than half of all [[NFL]] players are classified as "obese" (BMI ≥ 30), and 1 in 4 are classified as "extremely obese" (BMI ≥ 35), according to the BMI metric.<ref>{{Cite web|url=https://www.webmd.com/fitness-exercise/news/20050301/many-nfl-players-fatter-than-couch-potatoes|title=Regular Exercise: How It Can Boost Your Health}}</ref> However, their mean [[body fat percentage]], 14%, is well within what is considered a healthy range.<ref>{{cite web|url=http://health.usnews.com/health-news/family-health/heart/articles/2009/05/26/nfl-players-not-at-increased-heart-risk|title=NFL Players Not at Increased Heart Risk: Study finds they showed no more signs of cardiovascular trouble than general male population}}</ref> Similarly, [[Sumo]] wrestlers are typically categorized by BMI as "severely obese" or "very severely obese"; but one study of college-aged Sumo wrestlers found that 40% of them were no longer categorized as obese when body fat percentage (with a cutoff of <25%) was used instead of BMI; this was attributed to their very high lean body mass.<ref name="Body composition and resting metabo">{{cite journal | vauthors = Yamauchi T, Abe T, Midorikawa T, Kondo M |title=Body composition and resting metabolic rate of Japanese college Sumo wrestlers and non-athlete students: are Sumo wrestlers obese? |journal=Anthropological Science |date=2004 |volume=112 |issue=2|pages=179–185 |doi=10.1537/ase.040210 |doi-access=free }}</ref>

Canada utilises BMI sparingly within their method of defining levels of obesity through use of the Edmonton Scale (for adult obesity). This scale also introduces factors such as Quality of Life, Mental Health & Mobility amongst others. In recent years, Canada chose to allow both Chile & Ireland to adapt their obesity guidelines to suit both countries' health systems. In Ireland, obesity is now defined as "a Complex, Chronic & Relapsing Disease".

==Effects on health==
<!-- [[Effects of obesity on health]] links here, please make corresponding changes if altering this section title or removing the anchor tag. -->
Obesity increases a person's risk of developing various metabolic diseases, [[cardiovascular disease]], [[osteoarthritis]], [[Alzheimer disease]], [[Depression (mood)|depression]], and certain types of cancer.<ref name=Bluher2019/> Depending on the degree of obesity and the presence of comorbid disorders, obesity is associated with an estimated 2–20 year shorter life expectancy.<ref name=Lancet2009/><ref name=Bluher2019>{{cite journal | vauthors = Blüher M | title = Obesity: global epidemiology and pathogenesis | journal = Nature Reviews. Endocrinology | volume = 15 | issue = 5 | pages = 288–298 | date = May 2019 | pmid = 30814686 | doi = 10.1038/s41574-019-0176-8 | s2cid = 71146382 }}</ref> High BMI is a marker of risk for, but not a direct cause of, diseases caused by diet and physical activity.<ref name=":0">{{cite journal | vauthors = Chiolero A | title = Why causality, and not prediction, should guide obesity prevention policy | journal = The Lancet. Public Health | volume = 3 | issue = 10 | pages = e461–e462 | date = October 2018 | pmid = 30177480 | doi = 10.1016/S2468-2667(18)30158-0 | doi-access = free }}</ref>

===Mortality===
Obesity is one of the leading [[preventable causes of death]] worldwide.<ref name=Barn1999>{{cite journal | vauthors = Barness LA, Opitz JM, Gilbert-Barness E | title = Obesity: genetic, molecular, and environmental aspects | journal = American Journal of Medical Genetics. Part A | volume = 143A | issue = 24 | pages = 3016–34 | date = December 2007 | pmid = 18000969 | doi = 10.1002/ajmg.a.32035 | s2cid = 7205587 }}</ref><ref>{{cite journal | vauthors = Mokdad AH, Marks JS, Stroup DF, Gerberding JL | title = Actual causes of death in the United States, 2000 | journal = JAMA | volume = 291 | issue = 10 | pages = 1238–45 | date = March 2004 | pmid = 15010446 | doi = 10.1001/jama.291.10.1238 | s2cid = 14589790 }}</ref><ref name=Allison>{{cite journal | vauthors = Allison DB, Fontaine KR, Manson JE, Stevens J, VanItallie TB | title = Annual deaths attributable to obesity in the United States | journal = JAMA | volume = 282 | issue = 16 | pages = 1530–8 | date = October 1999 | pmid = 10546692 | doi = 10.1001/jama.282.16.1530 | doi-access = free }}</ref> The mortality risk is lowest at a BMI of 20–25&nbsp;kg/m<sup>2</sup><ref>{{cite journal | vauthors = Aune D, Sen A, Prasad M, Norat T, Janszky I, Tonstad S, Romundstad P, Vatten LJ | title = BMI and all cause mortality: systematic review and non-linear dose-response meta-analysis of 230 cohort studies with 3.74 million deaths among 30.3 million participants | journal = BMJ | volume = 353 | article-number = i2156 | date = May 2016 | pmid = 27146380 | pmc = 4856854 | doi = 10.1136/bmj.i2156 }}</ref><ref name=Lancet2009>{{cite journal | vauthors = Whitlock G, Lewington S, Sherliker P, Clarke R, Emberson J, Halsey J, Qizilbash N, Collins R, Peto R | title = Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies | journal = Lancet | volume = 373 | issue = 9669 | pages = 1083–96 | date = March 2009 | pmid = 19299006 | pmc = 2662372 | doi = 10.1016/S0140-6736(09)60318-4 }}</ref><ref name=Lancet2016Mort/> in non-smokers and at 24–27&nbsp;kg/m<sup>2</sup> in current smokers, with risk increasing along with changes in either direction.<ref>{{cite journal | vauthors = Calle EE, Thun MJ, Petrelli JM, Rodriguez C, Heath CW | title = Body-mass index and mortality in a prospective cohort of U.S. adults | journal = The New England Journal of Medicine | volume = 341 | issue = 15 | pages = 1097–105 | date = October 1999 | pmid = 10511607 | doi = 10.1056/NEJM199910073411501 | doi-access = free }}</ref><ref name=Euro2008>{{cite journal | vauthors = Pischon T, Boeing H, Hoffmann K, Bergmann M, Schulze MB, Overvad K, van der Schouw YT, Spencer E, Moons KG, Tjønneland A, Halkjaer J, Jensen MK, Stegger J, Clavel-Chapelon F, Boutron-Ruault MC, Chajes V, Linseisen J, Kaaks R, Trichopoulou A, Trichopoulos D, Bamia C, Sieri S, Palli D, Tumino R, Vineis P, Panico S, Peeters PH, May AM, Bueno-de-Mesquita HB, van Duijnhoven FJ, Hallmans G, Weinehall L, Manjer J, Hedblad B, Lund E, Agudo A, Arriola L, Barricarte A, Navarro C, Martinez C, Quirós JR, Key T, Bingham S, Khaw KT, Boffetta P, Jenab M, Ferrari P, Riboli E | title = General and abdominal adiposity and risk of death in Europe | journal = The New England Journal of Medicine | volume = 359 | issue = 20 | pages = 2105–20 | date = November 2008 | pmid = 19005195 | doi = 10.1056/NEJMoa0801891 | s2cid = 23967973 | doi-access = free }}</ref> This appears to apply in at least four continents.<ref name=Lancet2016Mort>{{cite journal |collaboration=The Global BMI Mortality Collaboration |vauthors = Di Angelantonio E, Bhupathiraju S, Wormser D, Gao P, Kaptoge S, Berrington de Gonzalez A, Cairns BJ, Huxley R, Jackson C, Joshy G, Lewington S, Manson JE, Murphy N, Patel AV, Samet JM, Woodward M, Zheng W, Zhou M, Bansal N, Barricarte A, Carter B, Cerhan JR, Smith GD, Fang X, Franco OH, Green J, Halsey J, Hildebrand JS, Jung KJ, Korda RJ, McLerran DF, Moore SC, O'Keeffe LM, Paige E, Ramond A, Reeves GK, Rolland B, Sacerdote C, Sattar N, Sofianopoulou E, Stevens J, Thun M, Ueshima H, Yang L, Yun YD, Willeit P, Banks E, Beral V, Chen Z, Gapstur SM, Gunter MJ, Hartge P, Jee SH, Lam TH, Peto R, Potter JD, Willett WC, Thompson SG, Danesh J, Hu FB | title = Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents | journal = Lancet | volume = 388 | issue = 10046 | pages = 776–86 | date = August 2016 | pmid = 27423262 | pmc = 4995441 | doi = 10.1016/S0140-6736(16)30175-1 }}</ref> Other research suggests that the association of BMI and waist circumference with mortality is U- or J-shaped, while the association between [[waist-to-hip ratio]] and [[waist-to-height ratio]] with mortality is more positive.<ref>{{cite journal | vauthors = Carmienke S, Freitag MH, Pischon T, Schlattmann P, Fankhaenel T, Goebel H, Gensichen J | title = General and abdominal obesity parameters and their combination in relation to mortality: a systematic review and meta-regression analysis | journal = European Journal of Clinical Nutrition | volume = 67 | issue = 6 | pages = 573–85 | date = June 2013 | pmid = 23511854 | doi = 10.1038/ejcn.2013.61 | doi-access = free }}</ref> In Asians the risk of negative health effects begins to increase between 22 and 25&nbsp;kg/m<sup>2</sup>.<ref>{{cite journal | title = Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies | journal = Lancet | volume = 363 | issue = 9403 | pages = 157–63 | date = January 2004 | pmid = 14726171 | doi = 10.1016/s0140-6736(03)15268-3 | author1 = WHO Expert Consultation | s2cid = 15637224 }}</ref> In 2021, the [[World Health Organization]] estimated that obesity caused at least 2.8 million deaths annually.<ref>{{cite web |title=Obesity |url=https://www.who.int/news-room/facts-in-pictures/detail/6-facts-on-obesity |website=who.int |access-date=9 September 2022 |language=en}}</ref> On average, obesity reduces life expectancy by six to seven&nbsp;years,<ref name=HaslamJames/><ref>{{cite journal | vauthors = Peeters A, Barendregt JJ, Willekens F, Mackenbach JP, Al Mamun A, Bonneux L | title = Obesity in adulthood and its consequences for life expectancy: a life-table analysis | journal = Annals of Internal Medicine | volume = 138 | issue = 1 | pages = 24–32 | date = January 2003 | pmid = 12513041 | doi = 10.7326/0003-4819-138-1-200301070-00008 | hdl = 1765/10043 | s2cid = 8120329 | url = http://espace.library.uq.edu.au/view/UQ:114024/n138_1_4.pdf | hdl-access = free }}</ref> a BMI of 30–35&nbsp;kg/m<sup>2</sup> reduces life expectancy by two to four years,<ref name=Lancet2009/> while severe obesity (BMI&nbsp;≥&nbsp;40&nbsp;kg/m<sup>2</sup>) reduces life expectancy by ten years.<ref name=Lancet2009/>

===Morbidity===
{{Main|Obesity-associated morbidity}}

Obesity increases the risk of many physical and mental conditions. These comorbidities are most commonly shown in [[metabolic syndrome]],<ref name="HaslamJames" /> a combination of medical disorders which includes: [[diabetes mellitus type 2]], [[hypertension|high blood pressure]], [[hypercholesterolemia|high blood cholesterol]], and [[hypertriglyceridemia|high triglyceride levels]].<ref>{{cite journal | vauthors = Grundy SM | title = Obesity, metabolic syndrome, and cardiovascular disease | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 89 | issue = 6 | pages = 2595–600 | date = June 2004 | doi = 10.1210/jc.2004-0372 | pmid = 15181029 | s2cid = 7453798 | doi-access =  }}</ref> A study from the [[RAK Hospital]] found that obese people are at a greater risk of developing [[long COVID]].<ref>{{cite web |title=Obesity linked to long Covid-19, RAK hospital study finds |url=https://www.msn.com/en-ae/news/middleeast/obesity-linked-to-long-covid-19-rak-hospital-study-finds/ar-AANeVeI |publisher=Khaleej Times|date=12 August 2021 |access-date=12 August 2021}}</ref> The CDC has found that obesity is the single strongest risk factor for severe COVID-19 illness.<ref>{{cite journal | vauthors = Kompaniyets L, Pennington AF, Goodman AB, Rosenblum HG, Belay B, Ko JY, Chevinsky JR, Schieber LZ, Summers AD, Lavery AM, Preston LE, Danielson ML, Cui Z, Namulanda G, Yusuf H, Mac Kenzie WR, Wong KK, Baggs J, Boehmer TK, Gundlapalli AV | title = Underlying Medical Conditions and Severe Illness Among 540,667 Adults Hospitalized With COVID-19, March 2020 – March 2021 | journal = Preventing Chronic Disease | volume = 18 | pages = E66 | date = July 2021 | article-number = 210123 | pmid = 34197283 | pmc = 8269743 | doi = 10.5888/pcd18.210123 | publisher = Centers for Disease Control and Prevention }}</ref>

Complications may be either directly caused by obesity or indirectly related through mechanisms sharing a common cause such as a poor diet or a [[sedentary lifestyle]]. The strength of the link between obesity and specific conditions varies. One of the strongest is the link with [[type 2 diabetes]]. Excess body fat underlies 64% of cases of diabetes in men and 77% of cases in women.<ref name = "Seidell_2005">{{cite book | vauthors = Seidell JC | chapter = Epidemiology – definition and classification of obesity | veditors = Kopelman PG, Caterson ID, Stock MJ, Dietz WH |title=Clinical obesity in adults and children: In Adults and Children |publisher=Blackwell Publishing |year=2005 |pages=[https://archive.org/details/clinicalobesityi02edunse/page/3 3–11] |isbn=978-1-4051-1672-5 |chapter-url=https://archive.org/details/clinicalobesityi02edunse/page/3 }}</ref>{{rp|9}}

Health consequences fall into two broad categories: those attributable to the effects of increased fat mass (such as [[osteoarthritis]], [[obstructive sleep apnea]], social stigmatization) and those due to the increased number of [[fat cells]] ([[diabetes mellitus|diabetes]], [[cancer]], [[cardiovascular disease]], [[non-alcoholic fatty liver disease]]).<ref name="HaslamJames" /><ref name="Bray2004">{{cite journal | vauthors = Bray GA | title = Medical consequences of obesity | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 89 | issue = 6 | pages = 2583–9 | date = June 2004 | pmid = 15181027 | doi = 10.1210/jc.2004-0535 | doi-access = free }}</ref> Increases in body fat alter the body's response to insulin, potentially leading to [[insulin resistance]]. Increased fat also creates a [[inflammation|proinflammatory state]],<ref>{{cite journal | vauthors = Shoelson SE, Herrero L, Naaz A | title = Obesity, inflammation, and insulin resistance | journal = Gastroenterology | volume = 132 | issue = 6 | pages = 2169–80 | date = May 2007 | pmid = 17498510 | doi = 10.1053/j.gastro.2007.03.059 }}</ref><ref>{{cite journal | vauthors = Shoelson SE, Lee J, Goldfine AB | title = Inflammation and insulin resistance | journal = The Journal of Clinical Investigation | volume = 116 | issue = 7 | pages = 1793–801 | date = July 2006 | pmid = 16823477 | pmc = 1483173 | doi = 10.1172/JCI29069 }}</ref> and a [[thrombosis|prothrombotic]] state.<ref name="Bray2004" /><ref>{{cite journal | vauthors = Dentali F, Squizzato A, Ageno W | title = The metabolic syndrome as a risk factor for venous and arterial thrombosis | journal = Seminars in Thrombosis and Hemostasis | volume = 35 | issue = 5 | pages = 451–7 | date = July 2009 | pmid = 19739035 | doi = 10.1055/s-0029-1234140 | s2cid = 260320617 }}</ref>

{| class="wikitable"
|-
! Medical field
! Condition
! Medical field
! Condition
|-
<!--Alphabetized-->| width="10%" | [[Cardiology]]
|
* [[Coronary heart disease]]:<ref>{{cite journal | vauthors = Lu Y, Hajifathalian K, Ezzati M, Woodward M, Rimm EB, Danaei G | title = Metabolic mediators of the effects of body-mass index, overweight, and obesity on coronary heart disease and stroke: a pooled analysis of 97 prospective cohorts with 1·8 million participants | journal = Lancet | volume = 383 | issue = 9921 | pages = 970–83 | date = March 2014 | pmid = 24269108 | pmc = 3959199 | doi = 10.1016/S0140-6736(13)61836-X }}</ref> [[angina pectoris|angina]] and [[myocardial infarction]]
* [[Congestive heart failure]]<ref name="HaslamJames" /><ref>{{cite journal | vauthors = Aune D, Sen A, Norat T, Janszky I, Romundstad P, Tonstad S, Vatten LJ | title = Body Mass Index, Abdominal Fatness, and Heart Failure Incidence and Mortality: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies | journal = Circulation | volume = 133 | issue = 7 | pages = 639–49 | date = February 2016 | pmid = 26746176 | doi = 10.1161/CIRCULATIONAHA.115.016801 | s2cid = 115876581 | doi-access = free }}</ref>
* [[High blood pressure]]<ref name="HaslamJames" />
* [[Dyslipidemia|Abnormal cholesterol levels]]<ref name="HaslamJames" />
* [[Deep vein thrombosis]] and [[pulmonary embolism]]<ref>{{cite journal | vauthors = Darvall KA, Sam RC, Silverman SH, Bradbury AW, Adam DJ | title = Obesity and thrombosis | journal = European Journal of Vascular and Endovascular Surgery | volume = 33 | issue = 2 | pages = 223–33 | date = February 2007 | pmid = 17185009 | doi = 10.1016/j.ejvs.2006.10.006 | doi-access = free }}</ref>
| <!--Alphabetized-->[[Dermatology]]
|
* [[Acanthosis nigricans]]<ref name="derm2007">{{cite journal | vauthors = Yosipovitch G, DeVore A, Dawn A | title = Obesity and the skin: skin physiology and skin manifestations of obesity | journal = Journal of the American Academy of Dermatology | volume = 56 | issue = 6 | pages = 901–16; quiz 917–20 | date = June 2007 | pmid = 17504714 | doi = 10.1016/j.jaad.2006.12.004 }}</ref>
* [[Lymphedema]]<ref name="derm2007" />
* [[Cellulitis]]<ref name="derm2007" />
* [[Hirsutism]]<ref name="derm2007" />
* [[Intertrigo]]<ref>{{cite journal | vauthors = Hahler B | title = An overview of dermatological conditions commonly associated with the obese patient | journal = Ostomy/Wound Management | volume = 52 | issue = 6 | pages = 34–6, 38, 40 passim | date = June 2006 | pmid = 16799182 }}</ref>
|-
| <!--Alphabetized-->[[Endocrinology]] and [[reproductive medicine]]
|
* [[Diabetes mellitus]]<ref name="HaslamJames" />
* [[Polycystic ovarian syndrome]]<ref name="HaslamJames" />
* [[menstruation|Menstrual]] disorders<ref name="HaslamJames" />
* [[Infertility]]<ref name="HaslamJames" /><ref name="OBGYN2008">{{cite journal | vauthors = Arendas K, Qiu Q, Gruslin A | title = Obesity in pregnancy: pre-conceptional to postpartum consequences | journal = Journal of Obstetrics and Gynaecology Canada | volume = 30 | issue = 6 | pages = 477–488 | date = June 2008 | pmid = 18611299 | doi = 10.1016/s1701-2163(16)32863-8 }}</ref>
* [[Maternal obesity|Complications during pregnancy]]<ref name="HaslamJames" /><ref name="OBGYN2008" />
* [[Birth defects]]<ref name="HaslamJames" />
* [[Stillbirth|Intrauterine fetal death]]<ref name="OBGYN2008" />
| <!--Alphabetized-->[[Gastroenterology]]
|
* [[Gastroesophageal reflux disease]]<ref name="Dibaise2013">{{Cite journal |vauthors=Dibaise JK, Foxx-Orenstein AE |date=July 2013 |title=Role of the gastroenterologist in managing obesity |journal=[[Expert Review of Gastroenterology & Hepatology]] |type=Review |volume=7 |issue=5 |pages=439–51 |doi=10.1586/17474124.2013.811061 |pmid=23899283|s2cid=26275773 }}</ref>
* [[Non-alcoholic fatty liver disease|Fatty liver disease]]<ref name="Dibaise2013" />
* [[Cholelithiasis]] (gallstones)<ref name="Dibaise2013" />
|-
| <!--Alphabetized-->[[Neurology]]
| style="width:40%;" |
* [[Stroke]]<ref name="HaslamJames" />
* [[Meralgia paresthetica]]<ref>{{cite journal | vauthors = Harney D, Patijn J | title = Meralgia paresthetica: diagnosis and management strategies | journal = Pain Medicine | volume = 8 | issue = 8 | pages = 669–77 | year = 2007 | pmid = 18028045 | doi = 10.1111/j.1526-4637.2006.00227.x | type = Review | doi-access = free }}</ref>
* [[Migraines]]<ref>{{cite journal | vauthors = Bigal ME, Lipton RB | title = Obesity and chronic daily headache | journal = Current Pain and Headache Reports | volume = 12 | issue = 1 | pages = 56–61 | date = January 2008 | pmid = 18417025 | doi = 10.1007/s11916-008-0011-8 | s2cid = 23729708 | type = Review }}</ref>
* [[Carpal tunnel syndrome]]<ref>{{cite journal | vauthors = Sharifi-Mollayousefi A, Yazdchi-Marandi M, Ayramlou H, Heidari P, Salavati A, Zarrintan S, Sharifi-Mollayousefi A | title = Assessment of body mass index and hand anthropometric measurements as independent risk factors for carpal tunnel syndrome | journal = Folia Morphologica | volume = 67 | issue = 1 | pages = 36–42 | date = February 2008 | pmid = 18335412 }}</ref>
* [[Dementia]]<ref>{{cite journal | vauthors = Beydoun MA, Beydoun HA, Wang Y | title = Obesity and central obesity as risk factors for incident dementia and its subtypes: a systematic review and meta-analysis | journal = Obesity Reviews | volume = 9 | issue = 3 | pages = 204–18 | date = May 2008 | pmid = 18331422 | pmc = 4887143 | doi = 10.1111/j.1467-789X.2008.00473.x | type = Meta-analysis }}</ref>
* [[Idiopathic intracranial hypertension]]<ref>{{cite journal | vauthors = Wall M | title = Idiopathic intracranial hypertension (pseudotumor cerebri) | journal = Current Neurology and Neuroscience Reports | volume = 8 | issue = 2 | pages = 87–93 | date = March 2008 | pmid = 18460275 | doi = 10.1007/s11910-008-0015-0 | s2cid = 17285706 | type = Review }}</ref>
* [[Multiple sclerosis]]<ref>{{cite journal | vauthors = Munger KL, Chitnis T, Ascherio A | title = Body size and risk of MS in two cohorts of US women | journal = Neurology | volume = 73 | issue = 19 | pages = 1543–50 | date = November 2009 | pmid = 19901245 | pmc = 2777074 | doi = 10.1212/WNL.0b013e3181c0d6e0 | type = Comparative Study }}</ref>
| <!--Alphabetized-->[[Oncology]]<ref>{{cite journal | vauthors = Basen-Engquist K, Chang M | title = Obesity and cancer risk: recent review and evidence | journal = Current Oncology Reports | volume = 13 | issue = 1 | pages = 71–6 | date = February 2011 | pmid = 21080117 | pmc = 3786180 | doi = 10.1007/s11912-010-0139-7 }}</ref>
|
* [[esophageal cancer|Esophageal]]
* [[colorectal cancer|Colorectal]]
* [[pancreatic cancer|Pancreatic]]
* [[Gallbladder cancer|Gallbladder]]
* [[Endometrial cancer|Endometrial]]
* [[Renal cell carcinoma|Kidney]]
* [[Leukemia]]
* [[Hepatocellular carcinoma]]<ref name="Dibaise2013" />
* [[Melanoma]]
|-
| style="width:10%;" | <!--Alphabetized-->[[Psychiatry]]
| style="width:40%;" |
* [[Major depressive disorder|Depression]] in women<ref name="HaslamJames" />
* Social [[Social stigma|stigmatization]]<ref name="HaslamJames" />
| <!--Alphabetized-->[[Respirology]]
|
* [[Sleep apnea|Obstructive sleep apnea]]<ref name="HaslamJames" /><ref name="Poulain">{{cite journal | vauthors = Poulain M, Doucet M, Major GC, Drapeau V, Sériès F, Boulet LP, Tremblay A, Maltais F | title = The effect of obesity on chronic respiratory diseases: pathophysiology and therapeutic strategies | journal = CMAJ | volume = 174 | issue = 9 | pages = 1293–9 | date = April 2006 | pmid = 16636330 | pmc = 1435949 | doi = 10.1503/cmaj.051299 }}</ref>
* [[Obesity hypoventilation syndrome]]<ref name="HaslamJames" /><ref name="Poulain" />
* [[Asthma]]<ref name="HaslamJames" /><ref name="Poulain" />
* Increased complications during [[general anaesthesia]]<ref name="HaslamJames" />
* increased risk of severe COVID-19<ref name="Poly 620044">{{cite journal | vauthors = Poly TN, Islam MM, Yang HC, Lin MC, Jian WS, Hsu MH, Jack Li YC | title = Obesity and Mortality Among Patients Diagnosed With COVID-19: A Systematic Review and Meta-Analysis | journal = Frontiers in Medicine | volume = 8 | article-number = 620044 | date = 5 February 2021 | pmid = 33634150 | pmc = 7901910 | doi = 10.3389/fmed.2021.620044 | doi-access = free }}</ref>
|-
| <!--Alphabetized-->[[Rheumatology]] and [[orthopedics]]
|
* [[Gout]]<ref>{{cite journal | vauthors = Aune D, Norat T, Vatten LJ | title = Body mass index and the risk of gout: a systematic review and dose-response meta-analysis of prospective studies | journal = European Journal of Nutrition | volume = 53 | issue = 8 | pages = 1591–601 | date = December 2014 | pmid = 25209031 | doi = 10.1007/s00394-014-0766-0 | s2cid = 38095938 }}</ref>
* Poor mobility<ref>{{cite journal | vauthors = Tukker A, Visscher TL, Picavet HS | title = Overweight and health problems of the lower extremities: osteoarthritis, pain and disability | journal = Public Health Nutrition | volume = 12 | issue = 3 | pages = 359–68 | date = March 2009 | pmid = 18426630 | doi = 10.1017/S1368980008002103 | type = Research Support | doi-access = free }}</ref>
* [[Osteoarthritis]]<ref name="HaslamJames" />
* [[Low back pain]]<ref>{{cite journal | vauthors = Molenaar EA, Numans ME, van Ameijden EJ, Grobbee DE | title = [Considerable comorbidity in overweight adults: results from the Utrecht Health Project] | language = nl | journal = Nederlands Tijdschrift voor Geneeskunde | volume = 152 | issue = 45 | pages = 2457–63 | date = November 2008 | pmid = 19051798 | type = English abstract }}</ref>
| <!--Alphabetized-->[[Urology]] and [[Nephrology]]
|
* [[Erectile dysfunction]]<ref>{{cite journal | vauthors = Corona G, Rastrelli G, Filippi S, Vignozzi L, Mannucci E, Maggi M | title = Erectile dysfunction and central obesity: an Italian perspective | journal = Asian Journal of Andrology | volume = 16 | issue = 4 | pages = 581–91 | date = 2014 | pmid = 24713832 | pmc = 4104087 | doi = 10.4103/1008-682X.126386 | doi-access = free }}</ref>
* [[Urinary incontinence]]<ref>{{cite journal | vauthors = Hunskaar S | title = A systematic review of overweight and obesity as risk factors and targets for clinical intervention for urinary incontinence in women | journal = Neurourology and Urodynamics | volume = 27 | issue = 8 | pages = 749–57 | year = 2008 | pmid = 18951445 | doi = 10.1002/nau.20635 | s2cid = 20378183 | type = Review | doi-access = free }}</ref>
* [[Chronic renal failure]]<ref>{{cite journal | vauthors = Ejerblad E, Fored CM, Lindblad P, Fryzek J, McLaughlin JK, Nyrén O | title = Obesity and risk for chronic renal failure | journal = Journal of the American Society of Nephrology | volume = 17 | issue = 6 | pages = 1695–702 | date = June 2006 | pmid = 16641153 | doi = 10.1681/ASN.2005060638 | type = Research Support | doi-access = free }}</ref>
* [[Hypogonadism]]<ref>{{cite journal | vauthors = Makhsida N, Shah J, Yan G, Fisch H, Shabsigh R | title = Hypogonadism and metabolic syndrome: implications for testosterone therapy | journal = The Journal of Urology | volume = 174 | issue = 3 | pages = 827–34 | date = September 2005 | pmid = 16093964 | doi = 10.1097/01.ju.0000169490.78443.59 | type = Review | citeseerx = 10.1.1.612.1060 }}</ref>
* [[Buried penis]]<ref name="pmid19935302">{{cite journal | vauthors = Pestana IA, Greenfield JM, Walsh M, Donatucci CF, Erdmann D | title = Management of "buried" penis in adulthood: an overview | journal = Plastic and Reconstructive Surgery | volume = 124 | issue = 4 | pages = 1186–95 | date = October 2009 | pmid = 19935302 | doi = 10.1097/PRS.0b013e3181b5a37f | s2cid = 36775257 | type = Review }}</ref>
|}

==== Metrics of health ====
{{Main|Metabolically healthy obesity}}

Newer research has focused on methods of identifying healthier obese people by clinicians, and not treating obese people as a monolithic group.<ref>{{cite journal | vauthors = Denis GV, Hamilton JA | title = Healthy obese persons: how can they be identified and do metabolic profiles stratify risk? | journal = Current Opinion in Endocrinology, Diabetes, and Obesity | volume = 20 | issue = 5 | pages = 369–376 | date = October 2013 | pmid = 23974763 | pmc = 3934493 | doi = 10.1097/01.med.0000433058.78485.b3 }}</ref> Obese people who do not experience medical complications from their obesity are sometimes called ''[[metabolically healthy obese|(metabolically) healthy obese]]'', but the extent to which this group exists (especially among older people) is in dispute.<ref name=":3">{{cite journal | vauthors = Blüher M | title = Metabolically Healthy Obesity | journal = Endocrine Reviews | volume = 41 | issue = 3 | article-number = bnaa004 | date = May 2020 | pmid = 32128581 | pmc = 7098708 | doi = 10.1210/endrev/bnaa004 }}</ref> The number of people considered ''metabolically healthy'' depends on the definition used, and there is no universally accepted definition.<ref name=":4"/> There are numerous obese people who have relatively few metabolic abnormalities, and a minority of obese people have no medical complications.<ref name=":4">{{cite journal | vauthors = Smith GI, Mittendorfer B, Klein S | title = Metabolically healthy obesity: facts and fantasies | journal = The Journal of Clinical Investigation | volume = 129 | issue = 10 | pages = 3978–3989 | date = October 2019 | pmid = 31524630 | pmc = 6763224 | doi = 10.1172/JCI129186 }}</ref> The guidelines of the [[American Association of Clinical Endocrinologists]] call for physicians to use [[risk stratification]] with obese patients when considering how to assess their risk of developing type 2 diabetes.<ref>{{cite journal | vauthors = Garvey WT, Mechanick JI, Brett EM, Garber AJ, Hurley DL, Jastreboff AM, Nadolsky K, Pessah-Pollack R, Plodkowski R | title = American Association of Clinical Endocrinologists and American College of Endocrinology Comprehensive Clinical Practice Guidelines for Medical Care of Patients with Obesity | journal = Endocrine Practice | volume = 22 | issue = Suppl 3 | pages = 1–203 | date = July 2016 | pmid = 27219496 | doi = 10.4158/EP161365.GL | s2cid = 3996442 | doi-access = free }}</ref>{{Rp|pages=59–60}}

In 2014, the BioSHaRE–[[European Union|EU]] Healthy Obese Project (sponsored by Maelstrom Research, a team under the [[Research Institute of the McGill University Health Centre]]) came up with two definitions for ''healthy obesity'', one more strict and one less so:<ref name=":3" /><ref>{{Cite journal |vauthors=van Vliet-Ostaptchouk JV, Nuotio M, Slagter SN, Doiron D, Fischer K, Foco L, Gaye A, Gögele M, Heier M, Hiekkalinna T, Joensuu A |date=February 2014 |title=The prevalence of metabolic syndrome and metabolically healthy obesity in Europe: a collaborative analysis of ten large cohort studies |journal=[[BMC Endocrine Disorders]] |publisher=[[BioMed Central]] ([[Springer Nature]]) |volume=14 |article-number=9 |doi=10.1186/1472-6823-14-9 |issn=1472-6823 |pmc=3923238 |pmid=24484869 |doi-access=free }}</ref>
{| class="wikitable" style="border:none"
|+BioSHaRE Healthy Obese (HOP) Project Criteria (2014)<br />{{Nobold|A patient must have a [[body mass index]] ≥ 30, and all of the following:}}
|style="border:0px"|
!Less strict
!More strict
|-
! colspan="3" |[[Blood pressure]] measured as follows, with no pharmaceutical help
|-
!Overall ([[mmHg]])
|≤ 140
|≤ 130
|-
![[Systole|Systolic]] (mmHg)
|<small>N/A</small>
|≤ 85{{Clarify|date=September 2023}}
|-
![[Diastolic]] (mmHg)
|≤ 90
|<small>N/A</small>
|-
! colspan="3" |[[Blood sugar level]] measured as follows, with no pharmaceutical help
|-
!Blood glucose ([[mmol]]/[[Litre|L]])
|≤ 7.0
|≤ 6.1
|-
! colspan="3" |[[Triglycerides]] measured as follows, with no pharmaceutical help
|-
!Fasting (mmol/L)
| colspan="2" |≤ 1.7
|-
!Non-fasting (mmol/L)
| colspan="2" |≤ 2.1
|-
! colspan="3" |[[High-density lipoprotein]] measured as follows, with no pharmaceutical help
|-
!Men (mmol/L)
| colspan="2" |> 1.03
|-
!Women (mmol/L)
| colspan="2" |> 1.3
|-
! colspan="3" |No diagnosis of any [[cardiovascular disease]]
|}

To come up with these criteria, BioSHaRE controlled for age and tobacco use, researching how both may effect the metabolic syndrome associated with obesity, but not found to exist in the metabolically healthy obese.<ref>{{Cite journal |vauthors=Stolk R |date=26 November 2013 |title=The Healthy Obese Project (HOP) |url=https://www.bioshare.eu/sites/default/files/BioSHaRE%20Newsletter%20Issue%204%2026%2011%2013.pdf |journal=BioSHaRE Newsletter |issue=4 |page=2 |archive-url=https://web.archive.org/web/20151023131837/https://www.bioshare.eu/sites/default/files/BioSHaRE%20Newsletter%20Issue%204%2026%2011%2013.pdf |archive-date=23 October 2015 |access-date=11 April 2022}}</ref> Other definitions of metabolically healthy obesity exist, including ones based on waist circumference rather than BMI, which is unreliable in certain individuals.<ref name=":4" />

Another identification metric for health in obese people is [[Triceps surae muscle|calf]] [[Muscle strength|strength]], which is positively correlated with [[physical fitness]] in obese people.<ref>{{Cite journal |vauthors=Scott D, Shore-Lorenti C, McMillan LB, Mesinovic J, Clark RA, Hayes A, Sanders KM, Duque G, Ebeling PR |date=March 2018 |title=Calf muscle density is independently associated with physical function in overweight and obese older adults |journal=Journal of Musculoskeletal and Neuronal Interactions |location=Likovrisi |publisher=Hylonome Publications |volume=18 |issue=1 |pages=9–17 |issn=1108-7161 |pmc=5881124 |pmid=29504574}}</ref> [[Body composition]] in general is hypothesized to help explain the existence of metabolically healthy obesity—the metabolically healthy obese are often found to have low amounts of [[Ectopia (medicine)|ectopic]] fat (fat stored in tissues other than adipose tissue) despite having overall fat mass equivalent in weight to obese people with [[metabolic syndrome]].<ref>{{Cite journal |vauthors=Karelis AD |date=October 2008 |title=Metabolically healthy but obese individuals |journal=[[The Lancet]] |language=en |volume=372 |issue=9646 |pages=1281–1283 |doi=10.1016/S0140-6736(08)61531-7|pmid=18929889 |s2cid=29584669 }}</ref>{{Rp|page=1282}}

===Survival paradox===
{{See also|Obesity paradox}}
Although the negative health consequences of obesity in the general population are well supported by the available research evidence, health outcomes in certain subgroups seem to be improved at an increased BMI, a phenomenon known as the obesity survival paradox.<ref name=Schmidt2007>{{cite journal | vauthors = Schmidt DS, Salahudeen AK | title = Obesity-survival paradox-still a controversy? | journal = Seminars in Dialysis | volume = 20 | issue = 6 | pages = 486–92 | year = 2007 | pmid = 17991192 | doi = 10.1111/j.1525-139X.2007.00349.x | s2cid = 37354831 | type = Review }}</ref> The paradox was first described in 1999 in overweight and obese people undergoing [[hemodialysis]]<ref name=Schmidt2007/> and has subsequently been found in those with [[heart failure]] and [[Peripheral vascular disease|peripheral artery disease]] (PAD).<ref name=paradox2003>{{cite journal |author=U.S. Preventive Services Task Force |title=Behavioral counseling in primary care to promote a healthy diet: recommendations and rationale |journal=American Family Physician |volume=67 |issue=12 |pages=2573–6 |date=June 2003 |pmid=12825847 |type=Review}}</ref>

In people with heart failure, those with a BMI between 30.0 and 34.9 had lower mortality than those with a normal weight. This has been attributed to the fact that people often lose weight as they become progressively more ill.<ref>{{cite journal | vauthors = Habbu A, Lakkis NM, Dokainish H | title = The obesity paradox: fact or fiction? | journal = The American Journal of Cardiology | volume = 98 | issue = 7 | pages = 944–8 | date = October 2006 | pmid = 16996880 | doi = 10.1016/j.amjcard.2006.04.039 | type = Review }}</ref> Similar findings have been made in other types of heart disease. People with class I obesity and heart disease do not have greater rates of further heart problems than people of normal weight who also have heart disease. In people with greater degrees of obesity, however, the risk of further cardiovascular events is increased.<ref>{{cite journal | vauthors = Romero-Corral A, Montori VM, Somers VK, Korinek J, Thomas RJ, Allison TG, Mookadam F, Lopez-Jimenez F | title = Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: a systematic review of cohort studies | journal = Lancet | volume = 368 | issue = 9536 | pages = 666–78 | date = August 2006 | pmid = 16920472 | doi = 10.1016/S0140-6736(06)69251-9 | s2cid = 23306195 | type = Review }}</ref><ref>{{cite journal | vauthors = Oreopoulos A, Padwal R, Kalantar-Zadeh K, Fonarow GC, Norris CM, McAlister FA | title = Body mass index and mortality in heart failure: a meta-analysis | journal = American Heart Journal | volume = 156 | issue = 1 | pages = 13–22 | date = July 2008 | pmid = 18585492 | doi = 10.1016/j.ahj.2008.02.014 | s2cid = 25332291 | type = Meta-analysis, Review | url = https://escholarship.org/uc/item/84z6x7fs }}</ref> Even after [[Coronary artery bypass surgery|cardiac bypass surgery]], no increase in mortality is seen in the overweight and obese.<ref>{{cite journal | vauthors = Oreopoulos A, Padwal R, Norris CM, Mullen JC, Pretorius V, Kalantar-Zadeh K | title = Effect of obesity on short- and long-term mortality postcoronary revascularization: a meta-analysis | journal = Obesity | volume = 16 | issue = 2 | pages = 442–50 | date = February 2008 | pmid = 18239657 | doi = 10.1038/oby.2007.36 | s2cid = 205524756 | type = Meta-analysis | url = https://escholarship.org/uc/item/75m3g7z6 | doi-access = free }}</ref> One study found that the improved survival could be explained by the more aggressive treatment obese people receive after a cardiac event.<ref>{{cite journal | vauthors = Diercks DB, Roe MT, Mulgund J, Pollack CV, Kirk JD, Gibler WB, Ohman EM, Smith SC, Boden WE, Peterson ED | title = The obesity paradox in non-ST-segment elevation acute coronary syndromes: results from the Can Rapid risk stratification of Unstable angina patients Suppress ADverse outcomes with Early implementation of the American College of Cardiology/American Heart Association Guidelines Quality Improvement Initiative | journal = American Heart Journal | volume = 152 | issue = 1 | pages = 140–8 | date = July 2006 | pmid = 16824844 | doi = 10.1016/j.ahj.2005.09.024 | type = Research Support }}</ref> Another study found that if one takes into account [[chronic obstructive pulmonary disease]] (COPD) in those with PAD, the benefit of obesity no longer exists.<ref name=paradox2003/>

==Causes==
The "[[a calorie is a calorie]]" model of obesity posits a combination of excessive [[food energy]] intake and a lack of [[physical activity]] as the cause of most cases of obesity.<ref name="CADG2006">{{cite journal |vauthors=Lau DC, Douketis JD, Morrison KM, Hramiak IM, Sharma AM, Ur E |date=April 2007 |title=2006 Canadian clinical practice guidelines on the management and prevention of obesity in adults and children [summary] |journal=CMAJ |type=Practice Guideline, Review |volume=176 |issue=8 |pages=S1–13 |doi=10.1503/cmaj.061409 |pmc=1839777 |pmid=17420481}}</ref> A limited number of cases are due primarily to genetics, medical reasons, or psychiatric illness.<ref name=Ble2008/> The [[satiety value]] shows that the feeling of [[satiety]] per [[calorie]] varies between food types.<ref>{{cite journal | last1 = Holt | first1 = SH | last2 = Miller | first2 = JC | last3 = Petocz | first3 = P | last4 = Farmakalidis | first4 = E | year = 1995 | title = A satiety index of common foods | journal = Eur J Clin Nutr | volume = 49 | issue = 9| pages = 675–690 | pmid = 7498104 }}</ref> Increasing rates of obesity at a societal level are felt to be due to an easily accessible and palatable [[Western pattern diet|diet]],<ref>{{cite journal | vauthors = Drewnowski A, Specter SE | title = Poverty and obesity: the role of energy density and energy costs | journal = The American Journal of Clinical Nutrition | volume = 79 | issue = 1 | pages = 6–16 | date = January 2004 | pmid = 14684391 | doi = 10.1093/ajcn/79.1.6 | type = Review | doi-access = free }}</ref> increased [[Effects of the car on societies|reliance on cars]], and mechanized manufacturing.<ref>{{cite journal | vauthors = Nestle M, Jacobson MF | title = Halting the obesity epidemic: a public health policy approach | journal = Public Health Reports | volume = 115 | issue = 1 | pages = 12–24 | year = 2000 | pmid = 10968581 | pmc = 1308552 | doi = 10.1093/phr/115.1.12 |doi-broken-date=12 July 2025 |jstor=4598478 | type = Research Support }}</ref><ref name=James2008>{{cite journal | vauthors = James WP | title = The fundamental drivers of the obesity epidemic | journal = Obesity Reviews | volume = 9 | issue = Suppl 1 | pages = 6–13 | date = March 2008 | pmid = 18307693 | doi = 10.1111/j.1467-789X.2007.00432.x | s2cid = 19894128 | type = Review }}</ref>

Some other factors have been proposed as causes towards rising rates of obesity worldwide, including [[sleep debt|insufficient sleep]], [[endocrine disruptor]]s, increased usage of certain medications (such as [[atypical antipsychotics]]),<ref>Masand PS. "Weight gain associated with psychotropic drugs". ''Expert opinion on pharmacotherapy.'' 2000;1:377–389.</ref> increases in ambient temperature, decreased rates of [[tobacco smoking|smoking]],<ref>
Baum, Charles L. "The effects of cigarette costs on BMI and obesity." ''Health Economics'' 18.1 (2009): 3-19. APA</ref> demographic changes, increasing maternal age of first-time mothers, changes to [[epigenetic]] regulation from the environment, increased phenotypic variance via [[assortative mating]], social pressure to [[dieting|diet]],<ref>{{cite journal | vauthors = Memon AN, Gowda AS, Rallabhandi B, Bidika E, Fayyaz H, Salib M, Cancarevic I | title = Have Our Attempts to Curb Obesity Done More Harm Than Good? | journal = Cureus | volume = 12 | issue = 9 | article-number = e10275 | date = September 2020 | pmid = 33042711 | doi = 10.7759/cureus.10275 | doi-access = free | pmc = 7538029 | s2cid = 221794897 }}</ref> among others. According to one study in 2006, factors like these may play as big of a role as excessive food energy intake and a lack of physical activity;<ref name="pmid16801930">{{cite journal | vauthors = Keith SW, Redden DT, Katzmarzyk PT, Boggiano MM, Hanlon EC, Benca RM, Ruden D, Pietrobelli A, Barger JL, Fontaine KR, Wang C, Aronne LJ, Wright SM, Baskin M, Dhurandhar NV, Lijoi MC, Grilo CM, DeLuca M, Westfall AO, Allison DB | title = Putative contributors to the secular increase in obesity: exploring the roads less traveled | journal = International Journal of Obesity | volume = 30 | issue = 11 | pages = 1585–1594 | date = November 2006 | pmid = 16801930 | doi = 10.1038/sj.ijo.0803326 | s2cid = 342831 | type = Review | doi-access =  }}</ref> however, the relative magnitudes of the effects of any proposed cause of obesity is varied and uncertain, as there is a general need for randomized controlled trials on humans before definitive statement can be made.<ref>{{Cite journal |last1=McAllister |first1=Emily J. |last2=Dhurandhar |first2=Nikhil V. |last3=Keith |first3=Scott W. |last4=Aronne |first4=Louis J. |last5=Barger |first5=Jamie |last6=Baskin |first6=Monica |last7=Benca |first7=Ruth M. |last8=Biggio |first8=Joseph |last9=Boggiano |first9=Mary M. |last10=Eisenmann |first10=Joe C. |last11=Elobeid |first11=Mai |last12=Fontaine |first12=Kevin R. |last13=Gluckman |first13=Peter |last14=Hanlon |first14=Erin C. |last15=Katzmarzyk |first15=Peter |date=2009 |title=Ten Putative Contributors to the Obesity Epidemic |journal=Critical Reviews in Food Science and Nutrition |language=en |volume=49 |issue=10 |pages=868–913 |doi=10.1080/10408390903372599 |pmc=2932668 |pmid=19960394}}</ref>

According to the [[Endocrine Society]], there is "growing evidence suggesting that obesity is a disorder of the [[energy homeostasis]] system, rather than simply arising from the passive accumulation of excess weight" and that "obesity pathogenesis involves two related but distinct processes: (1) sustained positive energy balance (energy [caloric] intake > energy expenditure) and (2) resetting of the body weight "set point" at an increased value."<ref name="pmid28898979" /> In other words, the fundamental cause of obesity is consuming more calories than are used by the body, and the body adapting to a heavier weight as the standard for the individual. 

===Diet===
{{Main|Diet and obesity}}
<div class="thumb tright" style="width: 417px; ">
<div class="thumbinner" >
<div style="float: left; margin: 1px; width: 202px">
<div class="thumbimage">[[File:World map of calory consumption 1961 (v2).svg|200px|alt=(Left) A world map with countries colored to reflect the food energy consumption of their people in 1961. North America, Europe, and Australia have relatively high intake, while Africa and Asia consume much less.]]
</div>
<div class="thumbcaption" style="clear:left">1961
</div>
</div><div style="float: left; margin: 1px; width: 202px">
<div class="thumbimage">[[File:World map of Energy consumption 2001-2003.svg|200px|alt=(Right) A world map with countries colored to reflect the food energy consumption of their people in 2001–2003. Consumption in North America, Europe, and Australia has increased with respect to previous levels in 1971. Food consumption has also increased substantially in many parts of Asia. However, food consumption in Africa remains low.]]
</div><div class="thumbcaption" style="clear:left">2001–03
</div>
</div><div class="thumbcaption" style="clear: left; text-align: left;">Map of dietary energy availability per person per day in 1961 (left) and 2001–2003 (right)<ref name=Earth09/> Calories per person per day (kilojoules per person per day)
{{Col-begin}}
{{Col-break}}
{{legend|#b3b3b3|<small>No data</small>}}
{{legend|#ffff65|<small><1,600 (<6,700)</small>}}
{{legend|#fff200|<small>1,600–1,800 (6,700–7,500)</small>}}
{{legend|#ffdc00|<small>1,800–2,000 (7,500–8,400)</small>}}
{{legend|#ffc600|<small>2,000–2,200 (8,400–9,200)</small>}}
{{legend|#ffb000|<small>2,200–2,400 (9,200–10,000)</small>}}
{{legend|#ff9a00|<small>2,400–2,600 (10,000–10,900)</small>}}
{{Col-break}}
{{legend|#ff8400|<small>2,600–2,800 (10,900–11,700)</small>}}
{{legend|#ff6e00|<small>2,800–3,000 (11,700–12,600)</small>}}
{{legend|#ff5800|<small>3,000–3,200 (12,600–13,400)</small>}}
{{legend|#ff4200|<small>3,200–3,400 (13,400–14,200)</small>}}
{{legend|#ff2c00|<small>3,400–3,600 (14,200–15,100)</small>}}
{{legend|#cb0000|<small>>3,600 (>15,100)</small>}}
{{col-end}}
</div>
</div>
</div>
[[File:World Per Person Energy Consumption.png|thumb|upright=1.6|alt=A graph showing a gradual increase in global food energy consumption per person per day between 1961 and 2002.|Average per capita energy consumption of the world from 1961 to 2002<ref name=Earth09>{{cite web|url=http://earthtrends.wri.org/searchable_db/index.php?theme=8&variable_ID=212&action=select_countries |title=EarthTrends: Nutrition: Calorie supply per capita |website=World Resources Institute |access-date=18 October 2009 |archive-url=https://web.archive.org/web/20110611160708/http://earthtrends.wri.org/searchable_db/index.php?theme=8&variable_ID=212&action=select_countries |archive-date=11 June 2011}}</ref>]]

Excess appetite for palatable, high-calorie food (especially fat, sugar, and certain animal proteins) is seen as the primary factor driving obesity worldwide, likely because of imbalances in [[neurotransmitter]]s affecting the drive to eat,<ref name=pharmaReview>{{cite journal | vauthors = Bojanowska E, Ciosek J | title = Can We Selectively Reduce Appetite for Energy-Dense Foods? An Overview of Pharmacological Strategies for Modification of Food Preference Behavior | journal = Current Neuropharmacology | volume = 14 | issue = 2 | pages = 118–42 | date = 15 February 2016 | pmid = 26549651 | pmc = 4825944 | doi = 10.2174/1570159X14666151109103147 }}</ref> as well as changes to the [[Duodenum#Obesity and Diabetes|duodenum impacting nutrient sensing and signaling]]. [[Dietary energy supply]] (the amount of calories in available food) per capita varies markedly between different regions and countries. It has also changed significantly over time.<ref name=Earth09/> From the early 1970s to the late 1990s the average [[food energy]] available per person per day (the amount of food bought) increased in all parts of the world except Eastern Europe. The United States had the highest availability with {{convert|3654|Cal}} per person in 1996.<ref name=Earth09/> This increased further in 2003 to {{convert|3754|Cal}}.<ref name=Earth09/> During the late 1990s, Europeans had {{convert|3394|Cal}} per person, in the developing areas of Asia there were {{convert|2648|Cal}} per person, and in sub-Saharan Africa people had {{convert|2176|Cal}} per person.<ref name=Earth09/><ref>{{cite web |url=https://www.scribd.com/doc/1470965/USDA-frsept99b |title=USDA: frsept99b |website=[[United States Department of Agriculture]] |access-date=10 January 2009 |archive-url=https://web.archive.org/web/20100603041758/http://www.scribd.com/doc/1470965/USDA-frsept99b |archive-date=3 June 2010 }}</ref> Total food energy consumption has been found to be related to obesity.<ref>{{cite web|url=https://www.statcan.gc.ca/pub/82-003-x/2009004/article/10933-eng.htm |title=Diet composition and obesity among Canadian adults |website=Statistics Canada }}</ref>
[[File:Prevalence of obesity in the adult population by region.svg|thumb|330x330px|Prevalence of obesity in the adult population by region (2000–2022)<ref>{{Cite book |last=FAO |url=https://openknowledge.fao.org/handle/20.500.14283/cd4313en |title=World Food and Agriculture – Statistical Yearbook 2025 |date=2025 |publisher=FAO |isbn=978-92-5-140174-3 |language=English |doi=10.4060/cd4313en}}</ref>]]
The widespread availability of [[Dietary Guidelines for Americans|dietary guidelines]]<ref>{{cite web|author=National Control for Health Statistics |title=Nutrition For Everyone |publisher=Centers for Disease Control and Prevention |url=https://www.cdc.gov/nccdphp/dnpa/nutrition/nutrition_for_everyone |access-date=9 July 2008}}</ref> has done little to address the problems of overeating and poor dietary choice.<ref>{{cite journal | vauthors = Marantz PR, Bird ED, Alderman MH | title = A call for higher standards of evidence for dietary guidelines | journal = American Journal of Preventive Medicine | volume = 34 | issue = 3 | pages = 234–40 | date = March 2008 | pmid = 18312812 | doi = 10.1016/j.amepre.2007.11.017 }}</ref> From 1971 to 2000, obesity rates in the United States increased from 14.5% to 30.9%.<ref name=Flegal2002>{{cite journal | vauthors = Flegal KM, Carroll MD, Ogden CL, Johnson CL | title = Prevalence and trends in obesity among US adults, 1999–2000 | journal = JAMA | volume = 288 | issue = 14 | pages = 1723–7 | date = October 2002 | pmid = 12365955 | doi = 10.1001/jama.288.14.1723 | doi-access = free }}</ref> During the same period, an increase occurred in the average amount of food energy consumed. For women, the average increase was {{convert|335|Cal}} per day ({{convert|1542|Cal}} in 1971 and {{convert|1877|Cal}} in 2004), while for men the average increase was {{convert|168|Cal}} per day ({{convert|2450|Cal}} in 1971 and {{convert|2618|Cal}} in 2004). Most of this extra food energy came from an increase in carbohydrate consumption rather than fat consumption.<ref>{{cite journal | title = Trends in intake of energy and macronutrients—United States, 1971–2000 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 53 | issue = 4 | pages = 80–2 | date = February 2004 | pmid = 14762332 | url = https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5304a3.htm | author1 = Centers for Disease Control Prevention (CDC) }}</ref> The primary sources of these extra carbohydrates are sweetened beverages, which now account for almost 25 percent of daily food energy in young adults in America,<ref name=Caballero>{{cite journal | vauthors = Caballero B | title = The global epidemic of obesity: an overview | journal = Epidemiologic Reviews | volume = 29 | pages = 1–5 | year = 2007 | pmid = 17569676 | doi = 10.1093/epirev/mxm012 | doi-access = free }}</ref> and potato chips.<ref>{{cite journal | vauthors = Mozaffarian D, Hao T, Rimm EB, Willett WC, Hu FB | title = Changes in diet and lifestyle and long-term weight gain in women and men | journal = The New England Journal of Medicine | volume = 364 | issue = 25 | pages = 2392–404 | date = June 2011 | pmid = 21696306 | pmc = 3151731 | doi = 10.1056/NEJMoa1014296 | type = Meta-analysis }}</ref> Consumption of [[sweetened beverages]] such as soft drinks, fruit drinks, and iced tea is believed to be contributing to the rising rates of obesity<ref>{{cite journal | vauthors = Malik VS, Schulze MB, Hu FB | title = Intake of sugar-sweetened beverages and weight gain: a systematic review | journal = The American Journal of Clinical Nutrition | volume = 84 | issue = 2 | pages = 274–88 | date = August 2006 | pmid = 16895873 | pmc = 3210834 | doi = 10.1093/ajcn/84.2.274 | type = Review }}</ref><ref>{{cite journal | vauthors = Olsen NJ, Heitmann BL | title = Intake of calorically sweetened beverages and obesity | journal = Obesity Reviews | volume = 10 | issue = 1 | pages = 68–75 | date = January 2009 | pmid = 18764885 | doi = 10.1111/j.1467-789X.2008.00523.x | s2cid = 28672221 | type = Review }}</ref> and to an increased risk of [[metabolic syndrome]] and [[type 2 diabetes]].<ref>{{cite journal | vauthors = Malik VS, Popkin BM, Bray GA, Després JP, Willett WC, Hu FB | title = Sugar-sweetened beverages and risk of metabolic syndrome and type 2 diabetes: a meta-analysis | journal = Diabetes Care | volume = 33 | issue = 11 | pages = 2477–83 | date = November 2010 | pmid = 20693348 | pmc = 2963518 | doi = 10.2337/dc10-1079 | type = Meta-analysis, Review }}</ref> [[Vitamin D deficiency]] is related to diseases associated with obesity.<ref name=WambergPedersen2015>{{cite journal | vauthors = Wamberg L, Pedersen SB, Rejnmark L, Richelsen B | title = Causes of Vitamin D Deficiency and Effect of Vitamin D Supplementation on Metabolic Complications in Obesity: a Review | journal = Current Obesity Reports | volume = 4 | issue = 4 | pages = 429–40 | date = December 2015 | pmid = 26353882 | doi = 10.1007/s13679-015-0176-5 | s2cid = 809587 }}</ref>

As societies become increasingly reliant on [[food energy|calorie-dense]], big-portions, and [[Fast food|fast-food]] meals, the association between fast-food consumption and obesity becomes more concerning.<ref>{{cite journal | vauthors = Rosenheck R | title = Fast food consumption and increased caloric intake: a systematic review of a trajectory towards weight gain and obesity risk | journal = Obesity Reviews | volume = 9 | issue = 6 | pages = 535–47 | date = November 2008 | pmid = 18346099 | doi = 10.1111/j.1467-789X.2008.00477.x | s2cid = 25820487 | type = Review | doi-access = free }}</ref> In the United States, consumption of fast-food meals tripled and food energy intake from these meals quadrupled between 1977 and 1995.<ref>{{cite book |vauthors=Lin BH, Guthrie J, Frazao E |editor=Frazão E |title=Agriculture Information Bulletin No. 750: America's Eating Habits: Changes and Consequences |chapter-url=http://www.ers.usda.gov/publications/aib-agricultural-information-bulletin/aib750.aspx |year=1999 |publisher=US Department of Agriculture, Economic Research Service |location=Washington, DC |pages=213–39 |chapter=Nutrient contribution of food away from home |archive-url=https://web.archive.org/web/20120708043622/http://www.ers.usda.gov/publications/aib-agricultural-information-bulletin/aib750.aspx |archive-date=8 July 2012 }}</ref>

[[Agricultural policy]] and [[Green Revolution (agriculture)|techniques]] in the United States and Europe have led to lower [[food prices]]. In the United States, subsidization of corn, soy, wheat, and rice through the [[U.S. farm bill]] has made the main sources of processed food cheap compared to fruits and vegetables.<ref>{{cite news| vauthors = Pollan M |title=You Are What You Grow |work=The New York Times |url=https://www.nytimes.com/2007/04/22/magazine/22wwlnlede.t.html |date=22 April 2007 |access-date=28 April 2021}}</ref> [[Calorie count laws]] and [[nutrition facts label]]s attempt to steer people toward making healthier food choices, including awareness of how much food energy is being consumed.

Obese people consistently under-report their food consumption as compared to people of normal weight.<ref>{{cite book | vauthors = Kopelman P, Caterson I | chapter = An overview of obesity management | veditors = Kopelman PG, Caterson ID, Stock MJ, Dietz WH |title=Clinical obesity in adults and children: In Adults and Children |publisher=Blackwell Publishing |year=2005 |pages=[https://archive.org/details/clinicalobesityi02edunse/page/319 319–326] (324) |isbn=978-1-4051-1672-5 |chapter-url=https://archive.org/details/clinicalobesityi02edunse/page/319 }}</ref> This is supported both by tests of people carried out in a [[calorimeter]] room<ref>{{cite book|title=Metabolism alone doesn't explain how thin people stay thin |publisher=The Medical Post | vauthors = Schieszer J }}</ref> and by direct observation.

===Sedentary lifestyle===
{{See also|Sedentary lifestyle|Exercise trends}}
A sedentary lifestyle may play a significant role in obesity.<ref name = "Seidell_2005" />{{rp|10}} Worldwide there has been a large shift towards less physically demanding work,<ref name=WHO2009>{{cite web|url=https://www.who.int/dietphysicalactivity/publications/facts/obesity/en/ |title=Obesity and overweight |website=World Health Organization |access-date=10 January 2009 |archive-url=https://web.archive.org/web/20081218104805/http://www.who.int/dietphysicalactivity/publications/facts/obesity/en/ |archive-date=18 December 2008}}</ref><ref name=WHOExercise>{{cite web |url=https://www.who.int/dietphysicalactivity/factsheet_inactivity/en/index.html |title=WHO &#124; Physical Inactivity: A Global Public Health Problem |website=World Health Organization|access-date=22 February 2009 |archive-date=13 February 2014 |archive-url=https://web.archive.org/web/20140213190030/http://www.who.int/dietphysicalactivity/factsheet_inactivity/en/index.html }}</ref><ref name=Ness2006>{{cite journal | vauthors = Ness-Abramof R, Apovian CM | title = Diet modification for treatment and prevention of obesity | journal = Endocrine | volume = 29 | issue = 1 | pages = 5–9 | date = February 2006 | pmid = 16622287 | doi = 10.1385/ENDO:29:1:135 | s2cid = 31964889 | type = Review }}</ref> and currently at least 30% of the world's population gets insufficient exercise.<ref name=WHOExercise/> This is primarily due to increasing use of mechanized transportation and a greater prevalence of labor-saving technology in the home.<ref name=WHO2009/><ref name=WHOExercise/><ref name=Ness2006/> In children, there appear to be declines in levels of physical activity (with particularly strong declines in the amount of walking and physical education), likely due to safety concerns, changes in social interaction (such as fewer relationships with neighborhood children), and inadequate urban design (such as too few public spaces for safe physical activity).<ref name="Pediatric Fitness">{{Cite book | vauthors = Salmon J, Timperio A | volume = 50 | pages = 183–99 | year = 2007 | pmid = 17387258 | doi = 10.1159/000101391 | isbn = 978-3-318-01396-2 | series = Medicine and Sport Science | type = Review | title = Pediatric Fitness | chapter = Prevalence, Trends and Environmental Influences on Child and Youth Physical Activity }}</ref> World trends in active leisure time [[physical activity]] are less clear. The World Health Organization indicates people worldwide are taking up less active recreational pursuits, while research from Finland<ref>{{cite journal | vauthors = Borodulin K, Laatikainen T, Juolevi A, Jousilahti P | title = Thirty-year trends of physical activity in relation to age, calendar time and birth cohort in Finnish adults | journal = European Journal of Public Health | volume = 18 | issue = 3 | pages = 339–44 | date = June 2008 | pmid = 17875578 | doi = 10.1093/eurpub/ckm092 | type = Research Support | doi-access = free }}</ref> found an increase and research from the United States found leisure-time physical activity has not changed significantly.<ref>{{cite journal | vauthors = Brownson RC, Boehmer TK, Luke DA | title = Declining rates of physical activity in the United States: what are the contributors? | journal = Annual Review of Public Health | volume = 26 | pages = 421–43 | year = 2005 | pmid = 15760296 | doi = 10.1146/annurev.publhealth.26.021304.144437 |doi-access=free| type = Review }}</ref> Physical activity in children may not be a significant contributor.<ref name=Wil2011>{{cite journal | vauthors = Wilks DC, Sharp SJ, Ekelund U, Thompson SG, Mander AP, Turner RM, Jebb SA, Lindroos AK | title = Objectively measured physical activity and fat mass in children: a bias-adjusted meta-analysis of prospective studies | journal = PLOS ONE | volume = 6 | issue = 2 | article-number = e17205 | date = February 2011 | pmid = 21383837 | pmc = 3044163 | doi = 10.1371/journal.pone.0017205 | bibcode = 2011PLoSO...617205W | doi-access = free }}</ref>

In both children and adults, there is an association between television viewing time and the risk of obesity.<ref>{{cite journal | vauthors = Gortmaker SL, Must A, Sobol AM, Peterson K, Colditz GA, Dietz WH | title = Television viewing as a cause of increasing obesity among children in the United States, 1986–1990 | journal = Archives of Pediatrics & Adolescent Medicine | volume = 150 | issue = 4 | pages = 356–62 | date = April 1996 | pmid = 8634729 | doi = 10.1001/archpedi.1996.02170290022003 | type = Review }}</ref><ref>{{cite journal | vauthors = Vioque J, Torres A, Quiles J | title = Time spent watching television, sleep duration and obesity in adults living in Valencia, Spain | journal = International Journal of Obesity and Related Metabolic Disorders | volume = 24 | issue = 12 | pages = 1683–8 | date = December 2000 | pmid = 11126224 | doi = 10.1038/sj.ijo.0801434 | s2cid = 26129544 | type = Research Support | doi-access =  }}</ref><ref>{{cite journal | vauthors = Tucker LA, Bagwell M | title = Television viewing and obesity in adult females | journal = American Journal of Public Health | volume = 81 | issue = 7 | pages = 908–11 | date = July 1991 | pmid = 2053671 | pmc = 1405200 | doi = 10.2105/AJPH.81.7.908 }}</ref> Increased media exposure increases the rate of childhood obesity, with rates increasing proportionally to time spent watching television.<ref>{{cite web|url=http://ipsdweb.ipsd.org/uploads/IPPC/CSM%20Media%20Health%20Report.pdf |title=Media + Child and Adolescent Health: A Systematic Review |publisher=Common Sense Media |year=2008 | vauthors = Emanuel EJ |access-date=6 April 2009}}</ref>

===Genetics===
{{Main|Genetics of obesity}}

{{update section|date=July 2021}}
[[File:La monstrua desnuda (1680), de Juan Carreño de Miranda..jpg|thumb|upright=1.3|alt=A painting of a dark haired pink cheeked obese nude young female leaning against a table. She is holding grapes and grape leaves in her left hand which cover her genitalia.|"La Monstrua Desnuda" (The Nude Monster), a 1680 painting by [[Juan Carreno de Miranda]] of a girl presumed to have [[Prader–Willi syndrome]]<ref>{{cite web |url=http://www.esst.org/newsletter2000.htm |title=Case Study: Cataplexy and SOREMPs Without Excessive Daytime Sleepiness in Prader Willi Syndrome. Is This the Beginning of Narcolepsy in a Five Year Old? | vauthors = Jones M |publisher=European Society of Sleep Technologists |access-date=6 April 2009 |url-status=live |archive-url=https://web.archive.org/web/20090413185433/http://www.esst.org/newsletter2000.htm |archive-date=13 April 2009 }}</ref>]]
Like many other medical conditions, obesity is the result of an interplay between genetic and environmental factors.<ref>{{cite journal | vauthors = Albuquerque D, Nóbrega C, Manco L, Padez C | title = The contribution of genetics and environment to obesity | journal = British Medical Bulletin | volume = 123 | issue = 1 | pages = 159–173 | date = September 2017 | pmid = 28910990 | doi = 10.1093/bmb/ldx022 | doi-access = free }}</ref> [[Polymorphism (biology)|Polymorphisms]] in various [[gene]]s controlling [[appetite]] and [[metabolism]] predispose to obesity when sufficient food energy is present. As of 2006, more than 41 of these sites on the human genome have been linked to the development of obesity when a favorable environment is present.<ref>{{cite journal | vauthors = Poirier P, Giles TD, Bray GA, Hong Y, Stern JS, Pi-Sunyer FX, Eckel RH | title = Obesity and cardiovascular disease: pathophysiology, evaluation, and effect of weight loss | journal = Arteriosclerosis, Thrombosis, and Vascular Biology | volume = 26 | issue = 5 | pages = 968–76 | date = May 2006 | pmid = 16627822 | doi = 10.1161/01.ATV.0000216787.85457.f3 | type = Review | citeseerx = 10.1.1.508.7066 | s2cid = 6052584 }}</ref> People with two copies of the [[FTO gene]] (fat mass and obesity associated gene) have been found on average to weigh 3–4&nbsp;kg more and have a 1.67-fold greater risk of obesity compared with those without the risk [[allele]].<ref>{{cite journal | vauthors = Loos RJ, Bouchard C | title = FTO: the first gene contributing to common forms of human obesity | journal = Obesity Reviews | volume = 9 | issue = 3 | pages = 246–50 | date = May 2008 | pmid = 18373508 | doi = 10.1111/j.1467-789X.2008.00481.x | s2cid = 23487924 | type = Review }}</ref> The differences in BMI between people that are [[heritability|due to genetics]] varies depending on the population examined from 6% to 85%.<ref>{{cite journal | vauthors = Yang W, Kelly T, He J | title = Genetic epidemiology of obesity | journal = Epidemiologic Reviews | volume = 29 | pages = 49–61 | year = 2007 | pmid = 17566051 | doi = 10.1093/epirev/mxm004 | type = Review | doi-access =  }}</ref>

Obesity is a major feature in several syndromes, such as [[Prader–Willi syndrome]], [[Bardet–Biedl syndrome]], [[Cohen syndrome]], and [[MOMO syndrome]]. (The term "non-syndromic obesity" is sometimes used to exclude these conditions.)<ref name="pmid19506576">{{cite journal | vauthors = Walley AJ, Asher JE, Froguel P | title = The genetic contribution to non-syndromic human obesity | journal = Nature Reviews. Genetics | volume = 10 | issue = 7 | pages = 431–42 | date = July 2009 | pmid = 19506576 | doi = 10.1038/nrg2594 | s2cid = 10870369 | type = Review }}</ref> In people with early-onset severe obesity (defined by an onset before 10&nbsp;years of age and body mass index over three [[standard deviation]]s above normal), 7% harbor a single point DNA mutation.<ref>{{cite journal | vauthors = Farooqi S, O'Rahilly S | title = Genetics of obesity in humans | journal = Endocrine Reviews | volume = 27 | issue = 7 | pages = 710–18 | date = December 2006 | pmid = 17122358 | doi = 10.1210/er.2006-0040 | type = Review | doi-access = free }}</ref>

Studies that have focused on inheritance patterns rather than on specific genes have found that 80% of the offspring of two [[parental obesity|obese parents]] were also obese, in contrast to less than 10% of the offspring of two parents who were of normal weight.<ref>{{cite book| vauthors = Kolata G |title=Rethinking thin: The new science of weight loss&nbsp;– and the myths and realities of dieting |publisher=Picador |year=2007 |page=122 |isbn=978-0-312-42785-6}}</ref> Different people exposed to the same environment have different risks of obesity due to their underlying genetics.<ref>{{cite journal | vauthors = Walley AJ, Asher JE, Froguel P | title = The genetic contribution to non-syndromic human obesity | journal = Nature Reviews. Genetics | volume = 10 | issue = 7 | pages = 431–42 | date = July 2009 | pmid = 19506576 | doi = 10.1038/nrg2594 | s2cid = 10870369 | type = Review | quote = However, it is also clear that genetics greatly influences this situation, giving individuals in the same 'obesogenic' environment significantly different risks of becoming obese. }}</ref>

The [[thrifty gene hypothesis]] postulates that, due to dietary scarcity during human evolution, people are prone to obesity. Their ability to take advantage of rare periods of abundance by storing energy as fat would be advantageous during times of varying food availability, and individuals with greater adipose reserves would be more likely to survive [[famine]]. This tendency to store fat, however, would be maladaptive in societies with stable food supplies.{{medcn|date=July 2021}} This theory has received various criticisms, and other evolutionarily-based theories such as the [[drifty gene hypothesis]] and the [[thrifty phenotype|thrifty phenotype hypothesis]] have also been proposed.{{medcn|date=July 2021}}

===Other illnesses===
Certain physical and mental illnesses and the pharmaceutical substances used to treat them can increase risk of obesity. Medical illnesses that increase obesity risk include several rare genetic syndromes (listed above) as well as some congenital or acquired conditions: [[hypothyroidism]], [[Cushing's syndrome]], [[growth hormone deficiency]],<ref>{{cite journal | vauthors = Rosén T, Bosaeus I, Tölli J, Lindstedt G, Bengtsson BA | title = Increased body fat mass and decreased extracellular fluid volume in adults with growth hormone deficiency | journal = Clinical Endocrinology | volume = 38 | issue = 1 | pages = 63–71 | date = January 1993 | pmid = 8435887 | doi = 10.1111/j.1365-2265.1993.tb00974.x | s2cid = 25725625 }}</ref> and some [[eating disorder]]s such as [[binge eating disorder]] and [[night eating syndrome]].<ref name=HaslamJames/> However, obesity is not regarded as a psychiatric disorder, and therefore is not listed in the [[Diagnostic and Statistical Manual of Mental Disorders|DSM-IVR]] as a psychiatric illness.<ref>{{cite journal | vauthors = Zametkin AJ, Zoon CK, Klein HW, Munson S | title = Psychiatric aspects of child and adolescent obesity: a review of the past 10 years | journal = Journal of the American Academy of Child and Adolescent Psychiatry | volume = 43 | issue = 2 | pages = 134–50 | date = February 2004 | pmid = 14726719 | doi = 10.1097/00004583-200402000-00008 | type = Review }}</ref> The risk of overweight and obesity is higher in patients with psychiatric disorders than in persons without psychiatric disorders.<ref>{{cite journal|vauthors=Chiles C, van Wattum PJ |title=Psychiatric aspects of the obesity crisis |journal=Psychiatr Times |year=2010 |volume=27 |issue=4 |pages=47–51}}</ref> Obesity and [[Depression (mood)|depression]] influence each other mutually, with obesity increasing the risk of clinical depression, and also depression leading to a higher chance of developing obesity.<ref name="Luppino2010rev">{{Cite journal |vauthors=Luppino FS, de Wit LM, Bouvy PF, Stijnen T, Cuijpers P, Penninx BW, Zitman FG |date=March 2010 |title=Overweight, obesity, and depression: a systematic review and meta-analysis of longitudinal studies |journal=Archives of General Psychiatry |volume=67 |issue=3 |pages=220–9 |doi=10.1001/archgenpsychiatry.2010.2 |pmid=20194822 |doi-access=free}}</ref>

=== Drug-induced obesity ===
Certain medications may cause weight gain or changes in [[body composition]]; these include [[insulin]], [[sulfonylurea]]s, [[thiazolidinedione]]s, [[atypical antipsychotic]]s, [[antidepressant]]s, [[glucocorticoids|steroids]], certain [[anticonvulsant]]s ([[phenytoin]] and [[valproate]]), [[pizotifen]], and some forms of [[hormonal contraception]].<ref name=HaslamJames/>

===Social determinants===
{{Main|Social determinants of obesity}}

[[File:Yamai no Soshi - Obesity.JPG|thumb|upright=1.3|The disease scroll (''Yamai no soshi'', late 12th century) depicts a woman moneylender with obesity, considered a disease of the rich.]]
[[File:More adults are obese in more unequal rich countries (cropped).jpg|thumb|upright=1.3|Obesity in developed countries is correlated with [[economic inequality]].]]

While genetic influences are important to understanding obesity, they cannot completely explain the dramatic increase seen within specific countries or globally.<ref>{{cite journal | vauthors = Yach D, Stuckler D, Brownell KD | title = Epidemiologic and economic consequences of the global epidemics of obesity and diabetes | journal = Nature Medicine | volume = 12 | issue = 1 | pages = 62–6 | date = January 2006 | pmid = 16397571 | doi = 10.1038/nm0106-62 | s2cid = 37456911 }}</ref>{{Better source needed|date=July 2021}} Though it is accepted that energy consumption in excess of energy expenditure leads to increases in body weight on an individual basis, the cause of the shifts in these two factors on the societal scale is much debated. There are a number of theories as to the cause but most believe it is a combination of various factors.

The correlation between [[social class]] and BMI varies globally. Research in 1989 found that in developed countries women of a high social class were less likely to be obese. No significant differences were seen among men of different social classes. In the developing world, women, men, and children from high social classes had greater rates of obesity.{{better source needed|date=July 2021}}<ref>{{cite journal|author-link2=Albert Stunkard| vauthors = Sobal J, Stunkard AJ | title = Socioeconomic status and obesity: a review of the literature | journal = Psychological Bulletin | volume = 105 | issue = 2 | pages = 260–75 | date = March 1989 | pmid = 2648443 | doi = 10.1037/0033-2909.105.2.260 | type = Review }}</ref> In 2007 repeating the same research found the same relationships, but they were weaker. The decrease in strength of correlation was felt to be due to the effects of [[globalization]].<ref name=McLaren2007>{{cite journal | vauthors = McLaren L | title = Socioeconomic status and obesity | journal = Epidemiologic Reviews | volume = 29 | pages = 29–48 | year = 2007 | pmid = 17478442 | doi = 10.1093/epirev/mxm001 | type = Review | doi-access = free }}</ref> Among developed countries, levels of adult obesity, and percentage of teenage children who are overweight, are correlated with [[economic inequality|income inequality]]. A similar relationship is seen among US states: more adults, even in higher social classes, are obese in more unequal states.<ref name="spirit">{{cite book|title=The Spirit Level: Why More Equal Societies Almost Always Do Better | vauthors = Wilkinson R, Picket K |author-link1=Richard G. Wilkinson |publisher=Allen Lane |location=London |isbn=978-1-84614-039-6 |year=2009 |pages=91–101|title-link=The Spirit Level: Why More Equal Societies Almost Always Do Better }}</ref>

Many explanations have been put forth for associations between BMI and social class. It is thought that in developed countries, the wealthy are able to afford more nutritious food, they are under greater social pressure to remain slim, and have more opportunities along with greater expectations for [[physical fitness]]. In [[undeveloped countries]] the ability to afford food, high energy expenditure with physical labor, and cultural values favoring a larger body size are believed to contribute to the observed patterns.<ref name=McLaren2007/> Attitudes toward body weight held by people in one's life may also play a role in obesity. A correlation in BMI changes over time has been found among friends, siblings, and spouses.<ref>{{cite journal | vauthors = Christakis NA, Fowler JH | title = The spread of obesity in a large social network over 32 years | journal = The New England Journal of Medicine | volume = 357 | issue = 4 | pages = 370–9 | date = July 2007 | pmid = 17652652 | doi = 10.1056/NEJMsa066082 | type = Research Support | citeseerx = 10.1.1.581.4893 | s2cid = 264194973 }}</ref> Stress and perceived low social status appear to increase risk of obesity.<ref name="spirit"/><ref>{{cite journal | vauthors = Björntorp P | title = Do stress reactions cause abdominal obesity and comorbidities? | journal = Obesity Reviews | volume = 2 | issue = 2 | pages = 73–86 | date = May 2001 | pmid = 12119665 | doi = 10.1046/j.1467-789x.2001.00027.x | s2cid = 23665421 }}</ref><ref>{{cite journal | vauthors = Goodman E, Adler NE, Daniels SR, Morrison JA, Slap GB, Dolan LM | title = Impact of objective and subjective social status on obesity in a biracial cohort of adolescents | journal = Obesity Research | volume = 11 | issue = 8 | pages = 1018–26 | date = August 2003 | pmid = 12917508 | doi = 10.1038/oby.2003.140 | type = Research Support }}</ref>

Smoking has a significant effect on an individual's weight. Those who quit smoking gain an average of 4.4&nbsp;kilograms (9.7&nbsp;lb) for men and 5.0&nbsp;kilograms (11.0&nbsp;lb) for women over ten years.<ref>{{cite journal | vauthors = Flegal KM, Troiano RP, Pamuk ER, Kuczmarski RJ, Campbell SM | title = The influence of smoking cessation on the prevalence of overweight in the United States | journal = The New England Journal of Medicine | volume = 333 | issue = 18 | pages = 1165–70 | date = November 1995 | pmid = 7565970 | doi = 10.1056/NEJM199511023331801 | doi-access = free }}</ref> However, changing rates of smoking have had little effect on the overall rates of obesity.<ref>{{cite journal | vauthors = Chiolero A, Faeh D, Paccaud F, Cornuz J | title = Consequences of smoking for body weight, body fat distribution, and insulin resistance | journal = The American Journal of Clinical Nutrition | volume = 87 | issue = 4 | pages = 801–9 | date = April 2008 | pmid = 18400700 | doi = 10.1093/ajcn/87.4.801 | type = Review | doi-access = free }}</ref>

In the United States, the number of children a person has is related to their risk of obesity. A woman's risk increases by 7% per child, while a man's risk increases by 4% per child.<ref>{{cite journal | vauthors = Weng HH, Bastian LA, Taylor DH, Moser BK, Ostbye T | title = Number of children associated with obesity in middle-aged women and men: results from the health and retirement study | journal = Journal of Women's Health | volume = 13 | issue = 1 | pages = 85–91 | year = 2004 | pmid = 15006281 | doi = 10.1089/154099904322836492 | type = Comparative Study }}</ref> This could be partly explained by the fact that having dependent children decreases physical activity in Western parents.<ref>{{cite journal | vauthors = Bellows-Riecken KH, Rhodes RE | title = A birth of inactivity? A review of physical activity and parenthood | journal = Preventive Medicine | volume = 46 | issue = 2 | pages = 99–110 | date = February 2008 | pmid = 17919713 | doi = 10.1016/j.ypmed.2007.08.003 | type = Review }}</ref>

In the developing world urbanization is playing a role in increasing rate of obesity. In China overall rates of obesity are below 5%; however, in some cities rates of obesity are greater than 20%.<ref>{{cite web|url=https://www.who.int/dietphysicalactivity/media/en/gsfs_obesity.pdf |title=Obesity and Overweight |publisher=[[World Health Organization]] |access-date=22 February 2009}}</ref> In part, this may be because of urban design issues (such as inadequate public spaces for physical activity).<ref name="Pediatric Fitness"/> Time spent in motor vehicles, as opposed to [[active transportation]] options such as cycling or walking, is correlated with increased risk of obesity.<ref>{{cite journal | vauthors = McCormack GR, Virk JS | title = Driving towards obesity: a systematized literature review on the association between motor vehicle travel time and distance and weight status in adults | journal = Preventive Medicine | volume = 66 | pages = 49–55 | date = September 2014 | pmid = 24929196 | doi = 10.1016/j.ypmed.2014.06.002 | hdl = 1880/115549 | s2cid = 12470420 | hdl-access = free }}</ref><ref>{{cite journal | vauthors = King DM, Jacobson SH | title = What Is Driving Obesity? A Review on the Connections Between Obesity and Motorized Transportation | journal = Current Obesity Reports | volume = 6 | issue = 1 | pages = 3–9 | date = March 2017 | pmid = 28243840 | doi = 10.1007/s13679-017-0238-y | s2cid = 207474312 }}</ref>

[[Malnutrition]] in early life is believed to play a role in the rising rates of obesity in the [[developing world]].<ref name=DC2001>{{cite journal | vauthors = Caballero B | title = Introduction. Symposium: Obesity in developing countries: biological and ecological factors | journal = The Journal of Nutrition | volume = 131 | issue = 3 | pages = 866S–870S | date = March 2001 | pmid = 11238776 | doi = 10.1093/jn/131.3.866s | type = Review | doi-access = free }}</ref> Endocrine changes that occur during periods of malnutrition may promote the storage of fat once more food energy becomes available.<ref name=DC2001/>

===Gut bacteria===
{{See also|Infectobesity}}
The study of the effect of infectious agents on metabolism is still in its early stages. [[Gut flora]] has been shown to differ between lean and obese people. There is an indication that gut flora can affect the metabolic potential. This apparent alteration is believed to confer a greater capacity to harvest energy contributing to obesity. Whether these differences are the direct cause or the result of obesity has yet to be determined unequivocally.<ref>{{cite journal | vauthors = DiBaise JK, Zhang H, Crowell MD, Krajmalnik-Brown R, Decker GA, Rittmann BE | title = Gut microbiota and its possible relationship with obesity | journal = Mayo Clinic Proceedings | volume = 83 | issue = 4 | pages = 460–9 | date = April 2008 | pmid = 18380992 | doi = 10.4065/83.4.460 | type = Review | doi-access = free }}</ref> The use of [[antibiotics]] among children has also been associated with obesity later in life.<ref>{{cite journal |title=Antibiotics: repeated treatments before the age of two could be a factor in obesity |journal=Prescrire International |date=2018 |url=http://english.prescrire.org/en/(X(1))/81/168/55076/0/2018/ArchiveNewsDetails.aspx?page=1 |access-date=2 July 2018}}</ref><ref name=Cox2015/>

An association between [[viruses]] and obesity has been found in humans and several different animal species. The amount that these associations may have contributed to the rising rate of obesity is yet to be determined.<ref>{{cite journal | vauthors = Falagas ME, Kompoti M | title = Obesity and infection | journal = The Lancet. Infectious Diseases | volume = 6 | issue = 7 | pages = 438–46 | date = July 2006 | pmid = 16790384 | doi = 10.1016/S1473-3099(06)70523-0 | type = Review }}</ref>

=== Other factors ===
Not getting enough sleep [[sleep and weight|is also associated with obesity]].<ref name=Cap2008>{{cite journal | vauthors = Cappuccio FP, Taggart FM, Kandala NB, Currie A, Peile E, Stranges S, Miller MA | title = Meta-analysis of short sleep duration and obesity in children and adults | journal = Sleep | volume = 31 | issue = 5 | pages = 619–626 | date = May 2008 | pmid = 18517032 | pmc = 2398753 | doi = 10.1093/sleep/31.5.619 }}</ref><ref>{{cite journal | vauthors = Miller MA, Kruisbrink M, Wallace J, Ji C, Cappuccio FP | title = Sleep duration and incidence of obesity in infants, children, and adolescents: a systematic review and meta-analysis of prospective studies | journal = Sleep | volume = 41 | issue = 4 | date = April 2018 | pmid = 29401314 | doi = 10.1093/sleep/zsy018 | doi-access = free }}</ref> Whether one causes the other is unclear.<ref name=Cap2008/> Even if short sleep does increase weight gain, it is unclear if this is to a meaningful degree or if increasing sleep would be of benefit.<ref>{{cite journal | vauthors = Horne J | title = Obesity and short sleep: unlikely bedfellows? | journal = Obesity Reviews | volume = 12 | issue = 5 | pages = e84–e94 | date = May 2011 | pmid = 21366837 | doi = 10.1111/j.1467-789X.2010.00847.x | s2cid = 23948346 | doi-access = free }}</ref>

Some have proposed that chemical compounds called "[[obesogens]]" may play a role in obesity.

Certain aspects of [[personality]] are associated with being obese.<ref name=Ger2014>{{cite journal | vauthors = Gerlach G, Herpertz S, Loeber S | title = Personality traits and obesity: a systematic review | journal = Obesity Reviews | volume = 16 | issue = 1 | pages = 32–63 | date = January 2015 | pmid = 25470329 | doi = 10.1111/obr.12235 | s2cid = 46500679 }}</ref> [[Loneliness]],<ref>{{cite journal | vauthors = Lauder W, Mummery K, Jones M, Caperchione C | title = A comparison of health behaviours in lonely and non-lonely populations | journal = Psychology, Health & Medicine | volume = 11 | issue = 2 | pages = 233–245 | date = May 2006 | pmid = 17129911 | doi = 10.1080/13548500500266607 | s2cid = 24974378 }}</ref> [[neuroticism]], [[impulsivity]], and sensitivity to reward are more common in people who are obese while [[conscientiousness]] and [[self-control]] are less common in people who are obese.<ref name=Ger2014/><ref>{{cite journal | vauthors = Jokela M, Hintsanen M, Hakulinen C, Batty GD, Nabi H, Singh-Manoux A, Kivimäki M | title = Association of personality with the development and persistence of obesity: a meta-analysis based on individual-participant data | journal = Obesity Reviews | volume = 14 | issue = 4 | pages = 315–323 | date = April 2013 | pmid = 23176713 | pmc = 3717171 | doi = 10.1111/obr.12007 | author6-link = Archana Singh-Manoux }}</ref> Because most of the studies on this topic are questionnaire-based, it is possible that these findings overestimate the relationships between personality and obesity: people who are obese might be aware of the [[social stigma of obesity]] and their questionnaire responses might be biased accordingly.<ref name=Ger2014 /> Similarly, the personalities of people who are obese as children might be influenced by obesity stigma, rather than these personality factors acting as risk factors for obesity.<ref name=Ger2014 />

In relation to globalization, it is known that trade liberalization is linked to obesity; research, based on data from 175 countries during 1975–2016, showed that obesity prevalence was positively correlated with trade openness, and the correlation was stronger in developing countries.<ref> {{cite journal | vauthors= An R et al |title=Trade openness and the obesity epidemic: a cross-national study of 175 countries during 1975-2016|journal=Annals of Epidemiology|volume=37|pages=31–36|date=July 2019|doi=10.1016/j.annepidem.2019.07.002 |pmid=31399309 }}</ref>

==Pathophysiology==
{{Main|Pathophysiology of obesity}}

[[File:Fatmouse.jpg|thumb|upright=1.3|alt=Two white mice both with similar sized ears, black eyes, and pink noses. The body of the mouse on the left, however, is about three times the width of the normal sized mouse on the right.|A comparison of a mouse unable to produce [[leptin]] thus resulting in obesity (left) and a normal mouse (right)]]

Two distinct but related processes are considered to be involved in the development of obesity: sustained positive energy balance (energy intake exceeding energy expenditure) and the resetting of the body weight "set point" at an increased value.<ref name="pmid28898979">{{cite journal| vauthors=Schwartz MW, Seeley RJ, Zeltser LM, Drewnowski A, Ravussin E, Redman LM | display-authors=etal| title=Obesity Pathogenesis: An Endocrine Society Scientific Statement. | journal=Endocr Rev | year= 2017 | volume= 38 | issue= 4 | pages= 267–296 | pmid=28898979 | doi=10.1210/er.2017-00111 | pmc=5546881}}</ref> The second process explains why finding effective obesity treatments has been difficult. While the underlying biology of this process still remains uncertain, research is beginning to clarify the mechanisms.<ref name="pmid28898979"/>

At a biological level, there are many possible [[pathophysiology|pathophysiological]] mechanisms involved in the development and maintenance of obesity.<ref name="flier">{{cite journal | vauthors = Flier JS | title = Obesity wars: molecular progress confronts an expanding epidemic | journal = Cell | volume = 116 | issue = 2 | pages = 337–50 | date = January 2004 | pmid = 14744442 | doi = 10.1016/S0092-8674(03)01081-X | s2cid = 6010027 | type = Review | doi-access = free }}</ref> This field of research had been almost unapproached until the [[leptin]] gene was discovered in 1994 by J. M. Friedman's laboratory.<ref>{{cite journal | vauthors = Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM | title = Positional cloning of the mouse obese gene and its human homologue | journal = Nature | volume = 372 | issue = 6505 | pages = 425–32 | date = December 1994 | pmid = 7984236 | doi = 10.1038/372425a0 | type = Research Support | bibcode = 1994Natur.372..425Z | s2cid = 4359725 }}</ref> While leptin and [[ghrelin]] are produced peripherally, they control appetite through their actions on the [[central nervous system]]. In particular, they and other appetite-related hormones act on the [[hypothalamus]], a region of the brain central to the regulation of food intake and energy expenditure. There are several circuits within the hypothalamus that contribute to its role in integrating appetite, the [[melanocortin]] pathway being the most well understood.<ref name="flier"/> The circuit begins with an area of the hypothalamus, the [[arcuate nucleus]], that has outputs to the [[lateral hypothalamus]] (LH) and [[ventromedial hypothalamus]] (VMH), the brain's feeding and satiety centers, respectively.<ref>{{cite book | vauthors = Boulpaep EL, Boron WF |title=Medical physiology: A cellular and molecular approach |publisher=Saunders |location=Philadelphia |year=2003 |page=1227 |isbn=978-0-7216-3256-8}}</ref>

The arcuate nucleus contains two distinct groups of [[neuron]]s.<ref name="flier"/> The first group coexpresses [[neuropeptide Y]] (NPY) and [[agouti-related peptide]] (AgRP) and has stimulatory inputs to the LH and inhibitory inputs to the VMH. The second group coexpresses [[pro-opiomelanocortin]] (POMC) and [[cocaine- and amphetamine-regulated transcript]] (CART) and has stimulatory inputs to the VMH and inhibitory inputs to the LH. Consequently, NPY/AgRP neurons stimulate feeding and inhibit satiety, while POMC/CART neurons stimulate satiety and inhibit feeding. Both groups of arcuate nucleus neurons are regulated in part by leptin. Leptin inhibits the NPY/AgRP group while stimulating the POMC/CART group. Thus a deficiency in leptin signaling, either via leptin deficiency or leptin resistance, leads to overfeeding and may account for some genetic and acquired forms of obesity.<ref name="flier"/>

==Management==
{{Main|Management of obesity}}

The main treatment for obesity consists of [[weight loss]] via lifestyle interventions, including prescribed [[Diet (nutrition)|diets]] and [[physical exercise]].<ref name="USGuidelines2013">{{cite journal | vauthors = Jensen MD, Ryan DH, Apovian CM, Ard JD, Comuzzie AG, Donato KA, Hu FB, Hubbard VS, Jakicic JM, Kushner RF, Loria CM, Millen BE, Nonas CA, Pi-Sunyer FX, Stevens J, Stevens VJ, Wadden TA, Wolfe BM, Yanovski SZ, Jordan HS, Kendall KA, Lux LJ, Mentor-Marcel R, Morgan LC, Trisolini MG, Wnek J, Anderson JL, Halperin JL, Albert NM, Bozkurt B, Brindis RG, Curtis LH, DeMets D, Hochman JS, Kovacs RJ, Ohman EM, Pressler SJ, Sellke FW, Shen WK, Smith SC, Tomaselli GF | title = 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and The Obesity Society | journal = Circulation | volume = 129 | issue = 25 Suppl 2 | pages = S102–S138 | date = June 2014 | pmid = 24222017 | pmc = 5819889 | doi = 10.1161/01.cir.0000437739.71477.ee }}</ref><ref name=CADG2006/><ref name="USDietaryGuidelines2015">{{cite web |author1=US Department of Health and Human Services. |title=2015–2020 Dietary Guidelines for Americans - health.gov |url=https://health.gov/dietaryguidelines/2015/ |website=health.gov |publisher=Skyhorse Publishing Inc. |access-date=30 September 2019 |date=2017 |archive-date=6 November 2019 |archive-url=https://web.archive.org/web/20191106200014/https://health.gov/dietaryguidelines/2015/ }}</ref><ref name="AACAHA2019">{{cite journal | vauthors = Arnett DK, Blumenthal RS, Albert MA, Buroker AB, Goldberger ZD, Hahn EJ, Himmelfarb CD, Khera A, Lloyd-Jones D, McEvoy JW, Michos ED, Miedema MD, Muñoz D, Smith SC, Virani SS, Williams KA, Yeboah J, Ziaeian B | title = 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines | journal = Circulation | volume = 140 | issue = 11 | pages = e596–e646 | date = September 2019 | pmid = 30879355 | pmc = 7734661 | doi = 10.1161/CIR.0000000000000678 | doi-access = free | author-link3 = Michelle Albert }}</ref> Although it is unclear what diets might support long-term weight loss, and although the effectiveness of [[Calorie restriction|low-calorie diets]] is debated,<ref name=Strychar /> lifestyle changes that reduce calorie consumption or increase physical exercise over the long term also tend to produce some sustained weight loss, despite slow weight regain over time.<ref name="USGuidelines2013"/><ref name=Strychar>{{cite journal | vauthors = Strychar I | title = Diet in the management of weight loss | journal = CMAJ | volume = 174 | issue = 1 | pages = 56–63 | date = January 2006 | pmid = 16389240 | pmc = 1319349 | doi = 10.1503/cmaj.045037 | type = Review }}</ref><ref>{{cite journal | vauthors = Shick SM, Wing RR, Klem ML, McGuire MT, Hill JO, Seagle H | title = Persons successful at long-term weight loss and maintenance continue to consume a low-energy, low-fat diet | journal = Journal of the American Dietetic Association | volume = 98 | issue = 4 | pages = 408–413 | date = April 1998 | pmid = 9550162 | doi = 10.1016/S0002-8223(98)00093-5 }}</ref><ref>{{cite journal | vauthors = Tate DF, Jeffery RW, Sherwood NE, Wing RR | title = Long-term weight losses associated with prescription of higher physical activity goals. Are higher levels of physical activity protective against weight regain? | journal = The American Journal of Clinical Nutrition | volume = 85 | issue = 4 | pages = 954–959 | date = April 2007 | pmid = 17413092 | doi = 10.1093/ajcn/85.4.954 | type = Randomized Controlled Trial | doi-access = free }}</ref>

Although 87% of participants in the [[National Weight Control Registry]] were able to maintain 10% body weight loss for 10 years,<ref>{{cite journal | vauthors = Thomas JG, Bond DS, Phelan S, Hill JO, Wing RR | title = Weight-loss maintenance for 10 years in the National Weight Control Registry | journal = American Journal of Preventive Medicine | volume = 46 | issue = 1 | pages = 17–23 | date = January 2014 | pmid = 24355667 | doi = 10.1016/j.amepre.2013.08.019 }}</ref>{{clarify|reason=unclear if this is sufficient weight loss to reduce BMI below the obesity cutoff and therefore effectively manage obesity|date=February 2022}} the most appropriate dietary approach for long term weight loss maintenance is still unknown.<ref name="Yannakoulia">{{cite journal | vauthors = Yannakoulia M, Poulimeneas D, Mamalaki E, Anastasiou CA | title = Dietary modifications for weight loss and weight loss maintenance | journal = Metabolism | volume = 92 | pages = 153–162 | date = March 2019 | pmid = 30625301 | doi = 10.1016/j.metabol.2019.01.001 | doi-access = free }}</ref> In the US, intensive behavioral interventions combining both dietary changes and exercise are recommended.<ref name="USGuidelines2013" /><ref name="USDietaryGuidelines2015" /><ref name=":7">{{cite journal |vauthors=Curry SJ, Krist AH, Owens DK, Barry MJ, Caughey AB, Davidson KW, Doubeni CA, Epling JW, Grossman DC, Kemper AR, Kubik M, Landefeld CS, Mangione CM, Phipps MG, Silverstein M, Simon MA, Tseng CW, Wong JB |date=September 2018 |title=Behavioral Weight Loss Interventions to Prevent Obesity-Related Morbidity and Mortality in Adults: US Preventive Services Task Force Recommendation Statement |journal=JAMA |volume=320 |issue=11 |pages=1163–1171 |doi=10.1001/jama.2018.13022 |pmid=30326502 |doi-access=free}}</ref> [[Intermittent fasting]] has no additional benefit of weight loss compared to continuous energy restriction.<ref name="Yannakoulia" /> Adherence is a more important factor in weight loss success than whatever kind of diet an individual undertakes.<ref name="Yannakoulia" /><ref>{{cite journal | vauthors = Gibson AA, Sainsbury A | title = Strategies to Improve Adherence to Dietary Weight Loss Interventions in Research and Real-World Settings | journal = Behavioral Sciences | volume = 7 | issue = 3 | page = 44 | date = July 2017 | pmid = 28696389 | pmc = 5618052 | doi = 10.3390/bs7030044 | doi-access = free }}</ref>

Several hypo-caloric diets are effective.<ref name="USGuidelines2013" /> In the short-term [[Low-carbohydrate diet|low carbohydrate diets]] appear better than [[Low-fat diet|low fat diets]] for weight loss.<ref name="SBU2013">{{Cite journal|url=https://www.sbu.se/en/publications/sbu-assesses/dietary-treatment-of-obesity/|title=Dietary treatment of obesity|journal=Annals of the New York Academy of Sciences|volume=499|issue=1|pages=250–263 | author =[[Swedish Agency for Health Technology Assessment and Assessment of Social Services]] (SBU)|access-date=17 June 2016|bibcode=1987NYASA.499..250B|year=1987|doi=10.1111/j.1749-6632.1987.tb36216.x|pmid=3300485|s2cid=45507530|url-access=subscription}}</ref> In the long term, however, all types of low-carbohydrate and low-fat diets appear equally beneficial.<ref name="SBU2013" /><ref>{{cite journal | vauthors = Johnston BC, Kanters S, Bandayrel K, Wu P, Naji F, Siemieniuk RA, Ball GD, Busse JW, Thorlund K, Guyatt G, Jansen JP, Mills EJ | title = Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis | journal = JAMA | volume = 312 | issue = 9 | pages = 923–33 | date = September 2014 | pmid = 25182101 | doi = 10.1001/jama.2014.10397 | doi-access =  }}</ref> Heart disease and diabetes risks associated with different diets appear to be similar.<ref>{{cite journal | vauthors = Naude CE, Schoonees A, Senekal M, Young T, Garner P, Volmink J | title = Low carbohydrate versus isoenergetic balanced diets for reducing weight and cardiovascular risk: a systematic review and meta-analysis | journal = PLOS ONE | volume = 9 | issue = 7 | article-number = e100652 | date = 2014 | pmid = 25007189 | pmc = 4090010 | doi = 10.1371/journal.pone.0100652 | type = Research Support | bibcode = 2014PLoSO...9j0652N | doi-access = free }}</ref>

Promotion of the Mediterranean diets among the obese may lower the risk of heart disease.<ref name="SBU2013" /> Decreased intake of [[sweet drink]]s is also related to weight-loss.<ref name="SBU2013" /> Success rates of long-term weight loss maintenance with lifestyle changes are low, ranging from 2–20%.<ref>{{cite journal | vauthors = Wing RR, Phelan S | title = Long-term weight loss maintenance | journal = The American Journal of Clinical Nutrition | volume = 82 | issue = 1 Suppl | pages = 222S–225S | date = July 2005 | pmid = 16002825 | doi =  10.1093/ajcn/82.1.222S| type = Review | doi-access = free }}</ref> Dietary and lifestyle changes are effective in limiting excessive weight gain in [[pregnancy]] and improve outcomes for both the mother and the child.<ref>{{cite journal | vauthors = Thangaratinam S, Rogozinska E, Jolly K, Glinkowski S, Roseboom T, Tomlinson JW, Kunz R, Mol BW, Coomarasamy A, Khan KS | title = Effects of interventions in pregnancy on maternal weight and obstetric outcomes: meta-analysis of randomised evidence | journal = BMJ | volume = 344 | article-number = e2088 | date = May 2012 | pmid = 22596383 | pmc = 3355191 | doi = 10.1136/bmj.e2088 | type = Meta-analysis }}</ref> Intensive behavioral counseling is recommended in those who are both obese and have other risk factors for heart disease.<ref>{{cite journal | vauthors = LeFevre ML | title = Behavioral counseling to promote a healthful diet and physical activity for cardiovascular disease prevention in adults with cardiovascular risk factors: U.S. Preventive Services Task Force Recommendation Statement | journal = Annals of Internal Medicine | volume = 161 | issue = 8 | pages = 587–93 | date = October 2014 | pmid = 25155419 | doi = 10.7326/M14-1796 | s2cid = 262280720 | doi-access =  }}</ref>

=== Health policy ===
[[File:Prevalence of obesity in the adult population, top countries (2022).svg|thumb|330x330px|Prevalence of obesity in the adult population, top countries (2022)<ref>{{Cite book |last=FAO |url=https://openknowledge.fao.org/handle/20.500.14283/cd4313en |title=World Food and Agriculture – Statistical Yearbook 2025 |date=2025 |publisher=FAO |isbn=978-92-5-140174-3 |language=English |doi=10.4060/cd4313en}}</ref>]]
[[File:Prevalence of obesity in the adult population (2022).svg|thumb|330x330px|Prevalence of obesity in the adult population in 2022<ref>{{Cite book |last=FAO |url=https://openknowledge.fao.org/handle/20.500.14283/cd4313en |title=World Food and Agriculture – Statistical Yearbook 2025 |date=2025 |publisher=FAO |isbn=978-92-5-140174-3 |language=English |doi=10.4060/cd4313en}}</ref>]]
Obesity is a complex public health and policy problem because of its prevalence, costs, and health effects.<ref>{{cite book |author=Satcher D |url=https://www.ncbi.nlm.nih.gov/books/NBK44206/ |title=The Surgeon General's Call to Action to Prevent and Decrease Overweight and Obesity |publisher=U.S. Dept. of Health and Human Services, Public Health Service, Office of Surgeon General |year=2001 |isbn=978-0-16-051005-2 |series=Publications and Reports of the Surgeon General}}</ref> As such, managing it requires changes in the wider societal context and effort by communities, local authorities, and governments.<ref name=":7" /> Public health efforts seek to understand and correct the [[Obesity and the environment|environmental factors]] responsible for the increasing prevalence of obesity in the population. Solutions look at changing the factors that cause excess food energy consumption and inhibit physical activity. Efforts include federally reimbursed meal programs in schools, limiting direct [[junk food|junk]] [[food marketing]] to children,<ref>{{cite news | vauthors = Barnes B |date=18 July 2007 |title=Limiting Ads of Junk Food to Children |work=The New York Times |url=https://www.nytimes.com/2007/07/18/business/18food.html |access-date=24 July 2008}}</ref> and decreasing access to sugar-sweetened beverages in schools.<ref>{{cite web |title=Fewer Sugary Drinks Key to Weight Loss |url=http://www.healthfinder.gov/news/newsstory.aspx?docID=625759 |access-date=18 October 2009 |website=U.S. Department of Health and Human Services |archive-date=16 November 2012 |archive-url=https://web.archive.org/web/20121116045620/http://www.healthfinder.gov/news/newsstory.aspx?docID=625759 }}</ref> The World Health Organization recommends the taxing of sugary drinks.<ref>{{cite web |title=WHO urges global action to curtail consumption and health impacts of sugary drinks |url=https://www.who.int/mediacentre/news/releases/2016/curtail-sugary-drinks/en/ |access-date=13 October 2016 |website=WHO}}</ref> When constructing urban environments, efforts have been made to increase access to parks and to develop pedestrian routes.<ref>{{cite journal |vauthors=Brennan Ramirez LK, Hoehner CM, Brownson RC, Cook R, Orleans CT, Hollander M, Barker DC, Bors P, Ewing R, Killingsworth R, Petersmarck K, Schmid T, Wilkinson W |date=December 2006 |title=Indicators of activity-friendly communities: an evidence-based consensus process |journal=American Journal of Preventive Medicine |type=Research Support |volume=31 |issue=6 |pages=515–24 |doi=10.1016/j.amepre.2006.07.026 |pmid=17169714|doi-access=free }}</ref> Efforts also exist to address the occurrence of [[Food swamp|food swamps]], or areas with an overabundance of convenient or fast food options, as these has been found to be strongly predictive of obesity rates.<ref>{{Cite journal |last1=Cooksey-Stowers |first1=Kristen |last2=Schwartz |first2=Marlene B. |last3=Brownell |first3=Kelly D. |date=2017-11-14 |title=Food Swamps Predict Obesity Rates Better Than Food Deserts in the United States |journal=International Journal of Environmental Research and Public Health |volume=14 |issue=11 |page=1366 |doi=10.3390/ijerph14111366 |doi-access=free |issn=1660-4601 |pmc=5708005 |pmid=29135909}}</ref>

[[Mass media]] campaigns seem to have limited effectiveness in changing behaviors that influence obesity, but may increase knowledge and awareness regarding physical activity and diet, which might lead to changes in the long term. Campaigns might also be able to reduce the amount of time spent [[Sedentary lifestyle|sitting or lying down]] and positively affect the intention to be active physically.<ref>{{cite journal | vauthors = Stead M, Angus K, Langley T, Katikireddi SV, Hinds K, Hilton S, Lewis S, Thomas J, Campbell M, Young B, Bauld L | title = Mass media to communicate public health messages in six health topic areas: a systematic review and other reviews of the evidence | language = EN | journal = Public Health Research | volume = 7 | issue = 8 | pages = 1–206 | date = May 2019 | pmid = 31046212 | doi = 10.3310/phr07080 | doi-access = free | hdl = 1893/29477 | hdl-access = free }}</ref><ref name=":6" /> [[Nutrition facts label|Nutritional labelling]] with energy information on menus might be able to help reducing energy intake while dining in restaurants.<ref>{{cite journal | vauthors = Crockett RA, King SE, Marteau TM, Prevost AT, Bignardi G, Roberts NW, Stubbs B, Hollands GJ, Jebb SA | title = Nutritional labelling for healthier food or non-alcoholic drink purchasing and consumption | journal = The Cochrane Database of Systematic Reviews | volume = 2 | issue = 2 | article-number = CD009315 | date = February 2018 | pmid = 29482264 | pmc = 5846184 | doi = 10.1002/14651858.CD009315.pub2 }}</ref> Some call for policy against [[ultra-processed foods]].<ref>{{cite journal | vauthors = Nestle M | title = Regulating the Food Industry: An Aspirational Agenda | journal = American Journal of Public Health | volume = 112 | issue = 6 | pages = 853–858 | date = June 2022 | pmid = 35446606 | pmc = 9137006 | doi = 10.2105/AJPH.2022.306844 }}</ref><ref>{{Cite news | vauthors = Finlay M, van Tulleken C, Miles ND, Onuchukwu T, Bury E |date=2023-04-20 |title=How did ultra-processed foods take over, and what are they doing to us? |language=en-GB |work=the Guardian |url=https://www.theguardian.com/science/audio/2023/apr/20/how-did-ultra-processed-foods-take-over-and-what-are-they-doing-to-us |access-date=2023-04-23 |issn=0261-3077}}</ref>

==Medical interventions==

=== Medication ===
{{Main|Anti-obesity medication}}

Since the introduction of medicines for the management of obesity in the 1930s, many compounds have been tried. Most of them reduce body weight by small amounts, and several of them are no longer marketed for obesity because of their side effects. Out of 25 anti-obesity medications withdrawn from the market between 1964 and 2009, 23 acted by altering the functions of chemical [[neurotransmitters]] in the brain. The most common side effects of these drugs that led to withdrawals were mental disturbances, cardiac side effects, and [[Substance abuse|drug abuse]] or [[drug dependence]]. Deaths were reportedly associated with seven products.<ref>{{cite journal | vauthors = Onakpoya IJ, Heneghan CJ, Aronson JK | title = Post-marketing withdrawal of anti-obesity medicinal products because of adverse drug reactions: a systematic review | journal = BMC Medicine | volume = 14 | issue = 1 | article-number = 191 | date = November 2016 | pmid = 27894343 | pmc = 5126837 | doi = 10.1186/s12916-016-0735-y | doi-access = free }}</ref>

Six medications for long-term use are: [[liraglutide]], [[naltrexone/bupropion]], [[orlistat]], [[semaglutide]], [[tirzepatide]] and [[phentermine/topiramate]].<ref name="Elmaleh-Sachs 2023">{{cite journal |last1=Elmaleh-Sachs |first1=Arielle |last2=Schwartz |first2=Jessica L. |last3=Bramante |first3=Carolyn T. |last4=Nicklas |first4=Jacinda M. |last5=Gudzune |first5=Kimberly A. |last6=Jay |first6=Melanie |title=Obesity Management in Adults: A Review |journal=JAMA |date=28 November 2023 |volume=330 |issue=20 |pages=2000–2015 |doi=10.1001/jama.2023.19897|pmid=38015216 |pmc=11325826 }}</ref> There is no information on how these drugs affect longer-term complications of obesity such as cardiovascular disease or death,<ref name="Yan2014" /> although studies on semaglutide have shown cardiovascular benefits.<ref name=McGowan/> After stopping treatment with [[GLP-1 receptor agonist|GLP-1 agonists]] such as semaglutide, liraglutide and tirzepatide, people regain on average more than half (50–70%) of the lost weight within 1 year.<ref name=McGowan>{{Cite journal |last1=McGowan |first1=Barbara |last2=Ciudin |first2=Andreea |last3=Baker |first3=Jennifer L. |last4=Busetto |first4=Luca |last5=Dicker |first5=Dror |last6=Frühbeck |first6=Gema |last7=Goossens |first7=Gijs H. |last8=Monami |first8=Matteo |last9=Sbraccia |first9=Paolo |date=2025-10-02 |title=A systematic review and meta-analysis of the efficacy and safety of pharmacological treatments for obesity in adults |journal=Nature Medicine |volume=31 |issue=10 |language=en |pages=3317–3329 |doi=10.1038/s41591-025-03978-z |pmid=41039116 |issn=1546-170X |doi-access=free|pmc=12532627 }}</ref><ref>{{Cite journal |last1=Quarenghi |first1=Massimo |last2=Capelli |first2=Silvia |last3=Galligani |first3=Giulia |last4=Giana |first4=Arianna |last5=Preatoni |first5=Giorgia |last6=Turri Quarenghi |first6=Rosamaria |date=2025-05-28 |title=Weight Regain After Liraglutide, Semaglutide or Tirzepatide Interruption: A Narrative Review of Randomized Studies |journal=Journal of Clinical Medicine |volume=14 |issue=11 |pages=3791 |doi=10.3390/jcm14113791 |doi-access=free |issn=2077-0383 |pmc=12155999 |pmid=40507553}}</ref>

In 2019 a [[systematic review]] compared the effects on weight of various doses of [[fluoxetine]] (60&nbsp;mg/d, 40&nbsp;mg/d, 20&nbsp;mg/d, 10&nbsp;mg/d) in obese adults.<ref name=":5">{{cite journal | vauthors = Serralde-Zúñiga AE, Gonzalez Garay AG, Rodríguez-Carmona Y, Melendez G | title = Fluoxetine for adults who are overweight or obese | journal = The Cochrane Database of Systematic Reviews | volume = 10 | issue = 10 | article-number = CD011688 | date = October 2019 | pmid = 31613390 | pmc = 6792438 | doi = 10.1002/14651858.CD011688.pub2 | collaboration = Cochrane Metabolic and Endocrine Disorders Group }}</ref> When compared to placebo, all dosages of fluoxetine appeared to contribute to weight loss but lead to increased risk of experiencing side effects such as dizziness, drowsiness, fatigue, insomnia and nausea during period of treatment. However, these conclusions were from low certainty evidence.<ref name=":5" /> When comparing, in the same review, the effects of fluoxetine on weight of obese adults, to other [[Anorectic|anti-obesity agents]], [[Omega-3 fatty acid|omega-3]] gel and not receiving a treatment, the authors could not reach conclusive results due to poor quality of evidence.<ref name=":5" />

Among antipsychotic drugs for treating schizophrenia [[clozapine]] is the most effective, but it also has the highest risk of causing the [[metabolic syndrome]], of which obesity is the main feature. For people who gain weight because of clozapine, taking [[metformin]] may reportedly improve three of the five components of the metabolic syndrome: waist circumference, fasting glucose, and fasting triglycerides.<ref>{{cite journal | vauthors = Siskind DJ, Leung J, Russell AW, Wysoczanski D, Kisely S | title = Metformin for Clozapine Associated Obesity: A Systematic Review and Meta-Analysis | journal = PLOS ONE | volume = 11 | issue = 6 | article-number = e0156208 | date = 15 June 2016 | pmid = 27304831 | pmc = 4909277 | doi = 10.1371/journal.pone.0156208 | bibcode = 2016PLoSO..1156208S | doi-access = free | veditors = Holscher C }}</ref>

=== Surgery ===
The most effective treatment for obesity is [[bariatric surgery]].<ref name=Col2014/><ref name="USGuidelines2013"/> The types of procedures include [[laparoscopic adjustable gastric banding]], [[Roux-en-Y gastric bypass]], [[vertical-sleeve gastrectomy]], and [[biliopancreatic diversion]].<ref name="NEJM 2017">{{cite journal | vauthors = Heymsfield SB, Wadden TA | title = Mechanisms, Pathophysiology, and Management of Obesity | journal = The New England Journal of Medicine | volume = 376 | issue = 3 | pages = 254–266 | date = January 2017 | pmid = 28099824 | doi = 10.1056/NEJMra1514009 | s2cid = 20407626 }}</ref> Surgery for severe obesity is associated with long-term weight loss, improvement in obesity-related conditions,<ref name=Chang2013>{{cite journal | vauthors = Chang SH, Stoll CR, Song J, Varela JE, Eagon CJ, Colditz GA | title = The effectiveness and risks of bariatric surgery: an updated systematic review and meta-analysis, 2003–2012 | journal = JAMA Surgery | volume = 149 | issue = 3 | pages = 275–87 | date = March 2014 | pmid = 24352617 | pmc = 3962512 | doi = 10.1001/jamasurg.2013.3654 | type = Meta-analysis, Review }}</ref> and decreased overall mortality; however, improved metabolic health results from the weight loss, not the surgery.<ref>{{cite journal|vauthors = Yoshino M, Kayser BD, Yoshino J, Stein RI, Reeds D, Eagon JC, Eckhouse SR, et al.|title=Effects of Diet versus Gastric Bypass on Metabolic Function in Diabetes|journal=New England Journal of Medicine|date=19 August 2020|doi=10.1056/NEJMoa2003697|volume=383|issue=8|pages=721–732|pmid=32813948|pmc=7456610}}</ref> One study found a weight loss of between 14% and 25% (depending on the type of procedure performed) at 10&nbsp;years, and a 29% reduction in all cause mortality when compared to standard weight loss measures.<ref>{{cite journal | vauthors = Sjöström L, Narbro K, Sjöström CD, Karason K, Larsson B, Wedel H, Lystig T, Sullivan M, Bouchard C, Carlsson B, Bengtsson C, Dahlgren S, Gummesson A, Jacobson P, Karlsson J, Lindroos AK, Lönroth H, Näslund I, Olbers T, Stenlöf K, Torgerson J, Agren G, Carlsson LM | title = Effects of bariatric surgery on mortality in Swedish obese subjects | journal = The New England Journal of Medicine | volume = 357 | issue = 8 | pages = 741–752 | date = August 2007 | pmid = 17715408 | doi = 10.1056/NEJMoa066254 | s2cid = 20533869 | type = Research Support | doi-access = free }}</ref> Complications occur in about 17% of cases and reoperation is needed in 7% of cases.<ref name=Chang2013/>

==Epidemiology==
{{Main|Epidemiology of obesity}}

[[File:Obesity rate (WHO, 2022).png|thumb|upright=1.4|Share of adults with BMIs > 30 (2022)]]

In earlier historical periods obesity was rare and achievable only by a small elite, although already recognised as a problem for health. But as prosperity increased in the [[Early Modern period]], it affected increasingly larger groups of the population.<ref name=Haslam2007/> Prior to the 1970s, obesity was a relatively rare condition even in the wealthiest of nations, and when it did exist it tended to occur among the wealthy. Then, a confluence of events started to change the human condition. The average BMI of populations in first-world countries started to increase, and consequently there was a rapid increase in the proportion of people overweight and obese.<ref>{{cite journal | vauthors = Prentice AM| title = The Double Burden of Malnutrition in Countries Passing through the Economic Transition | journal = Ann Nutr Metab | issue = suppl 3 | pages = 47–54 | date = 2018 | volume = 72 | doi = 10.1159/000487383 | pmid = 29635233 | s2cid = 4928218 | doi-access = free }}</ref>

In 1997, the WHO formally recognized obesity as a global epidemic.<ref name=Caballero/> As of 2008, the WHO estimates that at least 500&nbsp;million adults (greater than 10%) are obese, with higher rates among women than men.<ref name=WHO2009a>{{cite web|url=https://www.who.int/mediacentre/factsheets/fs311/en/index.html |title=Obesity and overweight |website=World Health Organization |access-date=8 April 2009}}</ref> The global prevalence of obesity more than doubled between 1980 and 2014. In 2014, more than 600 million adults were obese, equal to about 13 percent of the world's adult population,<ref>FAO, IFAD, UNICEF, WFP and WHO. 2017.The State of Food Security and Nutrition in the World 2017. Building resilience for peace and food security. Rome, FAO</ref> with that figure growing to 16% by 2022, according to the World Health Organization.<ref>{{Cite web |title=Obesity and overweight |url=https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight |access-date=2024-08-31 |website=www.who.int |language=en}}</ref> The percentage of adults affected in the United States as of 2015–2016 is about 39.6% overall (37.9% of males and 41.1% of females).<ref>{{cite journal | vauthors = Hales CM, Carroll MD, Fryar CD, Ogden CL | title = Prevalence of Obesity Among Adults and Youth: United States, 2015–2016 | journal = NCHS Data Brief | issue = 288 | pages = 1–8 | date = October 2017 | pmid = 29155689 }}</ref> In 2000, the [[World Health Organization]] (WHO) stated that [[overweight]] and obesity were replacing more traditional [[public health]] concerns such as [[undernutrition]] and [[infectious diseases]] as one of the most significant cause of poor health.<ref>{{Cite report |url=https://www.who.int/iris/handle/10665/42330#sthash.8pQS2f7r.dpuf |title=Obesity: preventing and managing the global epidemic |author=World Health Organization |date=2000 |publisher=World Health Organization |pages=1–2 |author-link=World Health Organization |access-date=1 February 2014}}</ref>

The rate of obesity also increases with age at least up to 50 or 60&nbsp;years old<ref name = "Seidell_2005" />{{rp|5}} and severe obesity in the United States, Australia, and Canada is increasing faster than the overall rate of obesity.<ref name=morbid2007/><ref name="pmid24351678">{{cite journal | vauthors = Howard NJ, Taylor AW, Gill TK, Chittleborough CR | title = Severe obesity: Investigating the socio-demographics within the extremes of body mass index | journal = Obesity Research & Clinical Practice | volume = 2 | issue = 1 | pages = I–II | date = March 2008 | pmid = 24351678 | doi = 10.1016/j.orcp.2008.01.001 }}</ref><ref name=Tjepkema2005>{{cite book|author=Tjepkema M |chapter=Measured Obesity–Adult obesity in Canada: Measured height and weight |title=Nutrition: Findings from the Canadian Community Health Survey |publisher=Statistics Canada |date=6 July 2005 |location=Ottawa, Ontario |chapter-url=https://www.statcan.gc.ca/pub/82-620-m/2005001/article/adults-adultes/8060-eng.htm}}</ref> The [[OECD]] has projected an increase in obesity rates until at least 2030, especially in the United States, Mexico and England with rates reaching 47%, 39% and 35%, respectively.<ref>{{cite web |url=https://www.oecd.org/els/health-systems/Obesity-Update-2017.pdf |title=Obesity Update 2017 |publisher=Organisation for Economic Co-operation and Development |access-date=6 October 2018}}</ref>

Once considered a problem only of high-income countries, obesity rates are rising worldwide and affecting both the developed and developing world.<ref name=EuroG2008>{{cite journal | vauthors = Tsigos C, Hainer V, Basdevant A, Finer N, Fried M, Mathus-Vliegen E, Micic D, Maislos M, Roman G, Schutz Y, Toplak H, Zahorska-Markiewicz B | title = Management of obesity in adults: European clinical practice guidelines | journal = Obesity Facts | volume = 1 | issue = 2 | pages = 106–16 | date = April 2008 | pmid = 20054170 | pmc = 6452117 | doi = 10.1159/000126822 | url = http://www.gojaznost.org/gs/dodatak/OMTFManagementofObesityinAdults2008.pdf | archive-url = https://web.archive.org/web/20120426034913/http://www.gojaznost.org/gs/dodatak/OMTFManagementofObesityinAdults2008.pdf | archive-date = 26 April 2012 }}</ref> These increases have been felt most dramatically in urban settings.<ref name=WHO2009a/>  In 2021, nearly half the global adult population - a billion men and 1.11 billion women aged 25 or older - were overweight or obese.  It was predicted  that if these trends continue about 57.4% of men and 60.3% of women would be overweight or obese by 2050.

Sex- and gender-based differences<ref>{{cite news |title=Over 50% of adults worldwide predicted to be obese or overweight by 2050 |url=https://www.bbc.co.uk/news/articles/cy87d2g81yxo |access-date=4 March 2025 |publisher=BBC News |date=4 March 2025}}</ref> influence the prevalence of obesity. Globally there are more obese women than men, but the numbers differ depending on how obesity is measured.<ref>{{cite journal | vauthors = Robertson C, Archibald D, Avenell A, Douglas F, Hoddinott P, van Teijlingen E, Boyers D, Stewart F, Boachie C, Fioratou E, Wilkins D, Street T, Carroll P, Fowler C | title = Systematic reviews of and integrated report on the quantitative, qualitative and economic evidence base for the management of obesity in men | journal = Health Technology Assessment | volume = 18 | issue = 35 | pages = v–vi, xxiii–xxix, 1–424 | date = May 2014 | pmid = 24857516 | pmc = 4781190 | doi = 10.3310/hta18350 }}</ref><ref>{{Cite journal |date=10 May 2016 |title=Managing obesity in men |url=https://evidence.nihr.ac.uk/collection/managing-obesity-in-men/ |access-date=7 December 2022 |website=NIHR Evidence |doi=10.3310/highlight-000844 |language=en-GB|url-access=subscription }}</ref>

==History==

===Etymology===
''Obesity'' is from the [[Latin]] ''obesitas'', which means "stout, fat, or plump". ''Ēsus'' is the past participle of ''edere'' (to eat), with ''ob'' (over) added to it.<ref name=etymol>{{cite web|url=https://www.etymonline.com/index.php?term=obesity |title=Online Etymology Dictionary: Obesity |website=Douglas Harper |access-date=31 December 2008}}</ref> ''[[The Oxford English Dictionary]]'' documents its first usage in 1611 by [[Randle Cotgrave]].<ref>{{cite web |url=http://www.oed.com/ |title=Obesity, n |website=[[Oxford English Dictionary]] 2008 |access-date=21 March 2009 |url-status=live |archive-url=https://web.archive.org/web/20080111125659/http://www.oed.com/ |archive-date=11 January 2008 }}</ref>

===Historical attitudes===
[[File:Charles Mellin (attributed) - Portrait of a Gentleman - Google Art Project.jpg|thumb|upright=1.0|alt=A very obese gentleman with a prominent double chin and mustache dressed in black with a sword at his left side.|During the [[Middle Ages]] and the [[Renaissance]] ''The Tuscan General [[Alessandro del Borro]]'', attributed to Charles Mellin, 1645<ref name=Zach2003>{{cite journal | vauthors = Bloomgarden ZT | title = Prevention of obesity and diabetes | journal = Diabetes Care | volume = 26 | issue = 11 | pages = 3172–8 | date = November 2003 | pmid = 14578257 | doi = 10.2337/diacare.26.11.3172 | url = http://care.diabetesjournals.org/content/26/11/3172.full | type = Review | doi-access = free }}</ref>]]
[[File:Venus von Willendorf 01.jpg|thumb|upright=1.0|alt=A carved stone miniature figurine depicted an obese female.|''[[Venus of Willendorf]]'' created 24,000–22,000 BC]]
[[Ancient Greek medicine]] recognizes obesity as a medical disorder and records that the Ancient Egyptians saw it in the same way.<ref name=Haslam2007>{{cite journal | vauthors = Haslam D | title = Obesity: a medical history | journal = Obesity Reviews | volume = 8 | issue = Suppl 1 | pages = 31–6 | date = March 2007 | pmid = 17316298 | doi = 10.1111/j.1467-789X.2007.00314.x | s2cid = 43866948 | type = Review | doi-access = free }}</ref> [[Hippocrates]] wrote that "Corpulence is not only a disease itself, but the harbinger of others".<ref name=HaslamJames/> The Indian surgeon [[Sushruta]] (6th century BCE) related obesity to diabetes and heart disorders.<ref name=Dwivedi&Dwivedi07/> He recommended physical work to help cure it and its side effects.<ref name=Dwivedi&Dwivedi07>{{cite web |url=http://medind.nic.in/iae/t07/i4/iaet07i4p243.pdf |title=History of Medicine: Sushruta – the Clinician – Teacher par Excellence |access-date=19 September 2008 |website=Dwivedi, Girish & Dwivedi, Shridhar |year=2007 |archive-url=https://web.archive.org/web/20081010045900/http://medind.nic.in/iae/t07/i4/iaet07i4p243.pdf |archive-date=10 October 2008 }}</ref> For most of human history, mankind struggled with food scarcity.<ref>{{cite book| vauthors = Mazzone T, Fantuzzi G |title=Adipose Tissue And Adipokines in Health And Disease (Nutrition and Health) |publisher=Humana Press |location=Totowa, NJ |year=2006 |page=222 |isbn=978-1-58829-721-1 }}</ref> Obesity has thus historically been viewed as a sign of wealth and prosperity. It was common among high officials in Ancient East Asian civilizations.<ref>{{cite book| vauthors = Keller K |title=Encyclopedia of Obesity |publisher=Sage Publications, Inc |location=Thousand Oaks, Calif |year=2008 |isbn=978-1-4129-5238-5 |url=https://books.google.com/books?id=aRp2rJrEqZsC | page = 49}}</ref> In the 17th century, English medical author [[Tobias Venner]] is credited with being one of the first to refer to the term as a societal disease in a published English language book.<ref name=Haslam2007/><ref>{{cite book |url= https://archive.org/details/fatboysslimbook00gilm|url-access=registration|quote=tobias venner obesity.|title=Fat Boys: A Slim Book| vauthors = Gilman SL |page=[https://archive.org/details/fatboysslimbook00gilm/page/18 18]|publisher= University of Nebraska Press|year=2004|isbn=978-0-8032-2183-3}}</ref>

With the onset of the [[Industrial Revolution]], it was realized that the military and economic might of nations were dependent on both the body size and strength of their soldiers and workers.<ref name=Caballero/> Increasing the average body mass index from what is now considered underweight to what is now the normal range played a significant role in the development of industrialized societies.<ref name=Caballero/> Height and weight thus both increased through the 19th&nbsp;century in the developed world. During the 20th century, as populations reached their genetic potential for height, weight began increasing much more than height, resulting in obesity.<ref name=Caballero/> In the 1950s, increasing wealth in the developed world decreased child mortality, but as body weight increased, heart and kidney disease became more common.<ref name=Caballero/><ref>{{cite journal | vauthors = Breslow L | title = Public health aspects of weight control | journal = American Journal of Public Health and the Nation's Health | volume = 42 | issue = 9 | pages = 1116–20 | date = September 1952 | pmid = 12976585 | pmc = 1526346 | doi = 10.2105/AJPH.42.9.1116 }}</ref>
During this time period, insurance companies realized the connection between weight and life expectancy and increased premiums for the obese.<ref name=HaslamJames/>

Many cultures throughout history have viewed obesity as the result of a character flaw. The ''obesus'' or fat character in [[Ancient Greek comedy]] was a glutton and figure of mockery. During Christian times, food was viewed as a gateway to the sins of [[Sloth (sin)|sloth]] and [[lust]].<ref name=Woodhouse/> In modern Western culture, excess weight is often regarded as unattractive, and obesity is commonly associated with various negative stereotypes. People of all ages can face social stigmatization and may be targeted by bullies or shunned by their peers.<ref name=Bias2001>{{cite journal | vauthors = Puhl R, Brownell KD | title = Bias, discrimination, and obesity | journal = Obesity Research | volume = 9 | issue = 12 | pages = 788–805 | date = December 2001 | pmid = 11743063 | doi = 10.1038/oby.2001.108 | type = Review | doi-access = free }}</ref>

Public perceptions in Western society regarding healthy body weight differ from those regarding the weight that is considered ideal – and both have changed since the beginning of the 20th century. The weight that is viewed as an ideal has become lower since the 1920s. This is illustrated by the fact that the average height of Miss America pageant winners increased by 2% from 1922 to 1999, while their average weight decreased by 12%.<ref>{{cite journal | vauthors = Rubinstein S, Caballero B | title = Is Miss America an undernourished role model? | journal = JAMA | volume = 283 | issue = 12 | page = 1569 | year = 2000 | pmid = 10735392 | doi = 10.1001/jama.283.12.1569 | type = Letter }}</ref> On the other hand, people's views concerning healthy weight have changed in the opposite direction. In Britain, the weight at which people considered themselves to be overweight was significantly higher in 2007 than in 1999.<ref name=John2008>{{cite journal | vauthors = Johnson F, Cooke L, Croker H, Wardle J | title = Changing perceptions of weight in Great Britain: comparison of two population surveys | journal = BMJ | volume = 337 | pages = a494 | date = July 2008 | pmid = 18617488 | pmc = 2500200 | doi = 10.1136/bmj.a494 }}</ref> These changes are believed to be due to increasing rates of adiposity leading to increased acceptance of extra body fat as being normal.<ref name=John2008/>

Obesity is still seen as a sign of wealth and well-being in many parts of Africa. This has become particularly common since the [[HIV]] epidemic began.<ref name=HaslamJames/>

===The arts===
The first sculptural representations of the human body 20,000–35,000&nbsp;years ago depict obese females. Some attribute the [[Venus figurines]] to the tendency to emphasize fertility while others feel they represent "fatness" in the people of the time.<ref name=Woodhouse/> Corpulence is, however, absent in both Greek and Roman art, probably in keeping with their ideals regarding moderation. This continued through much of Christian European history, with only those of low socioeconomic status being depicted as obese.<ref name=Woodhouse/>

During the [[Renaissance]] some of the upper class began flaunting their large size, as can be seen in portraits of [[Henry VIII of England]] and [[Alessandro dal Borro]].<ref name=Woodhouse/> [[Peter Paul Rubens|Rubens]] (1577–1640) regularly depicted heavyset women in his pictures, from which derives the term [[Peter Paul Rubens#Work|Rubenesque]]. These women, however, still maintained the "hourglass" shape with its relationship to fertility.<ref name=Fumento>{{cite book| vauthors = Fumento M |title=The Fat of the Land: Our Health Crisis and How Overweight Americans Can Help Themselves |publisher=Penguin (Non-Classics) |year=1997 |page=126 |isbn=978-0-14-026144-8}}</ref> During the 19th&nbsp;century, views on obesity changed in the Western world. After centuries of obesity being synonymous with wealth and social status, slimness began to be seen as the desirable standard.<ref name=Woodhouse/> In his 1819 print, ''The Belle Alliance, or the Female Reformers of Blackburn!!!,'' artist [[George Cruikshank]] criticised the work of female reformers in [[Blackburn]] and used fatness as a means to portray them as unfeminine.<ref>{{Cite journal| vauthors = Kitchener C |date=2022|title=Sisters of the Earth: The Landscapes, Radical Identities and Performances of Female Reformers in 1819 |journal=Journal for Eighteenth-Century Studies|language=en|volume=45|issue=1|pages=77–93|doi=10.1111/1754-0208.12778|s2cid=246984311|issn=1754-0208}}</ref>

==Society and culture==

===Economic impact===
In addition to its health impacts, obesity leads to many problems, including disadvantages in employment<ref name = "Puhl_2005">{{cite book | vauthors = Puhl R, Henderson K, Brownell K | chapter = Social consequences of obesity | veditors = Kopelman PG, Caterson ID, Stock MJ, Dietz WH |title=Clinical obesity in adults and children: In Adults and Children |publisher=Blackwell Publishing |year=2005 | chapter-url = https://archive.org/details/clinicalobesityi02edunse/page/29 | pages = 29–45 |isbn=978-1-4051-1672-5 |url=https://archive.org/details/clinicalobesityi02edunse/page/29 }}</ref>{{rp|29}}<ref>{{cite journal | vauthors = Johansson E, Böckerman P, Kiiskinen U, Heliövaara M | title = Obesity and labour market success in Finland: the difference between having a high BMI and being fat | journal = Economics and Human Biology | volume = 7 | issue = 1 | pages = 36–45 | date = March 2009 | pmid = 19249259 | doi = 10.1016/j.ehb.2009.01.008 }}</ref> and increased business costs. 

In 2005, the medical costs attributable to obesity in the US were an estimated $190.2&nbsp;billion or 20.6% of all medical expenditures,<ref name=medical-costs>{{cite journal | vauthors = Cawley J, Meyerhoefer C | title = The medical care costs of obesity: an instrumental variables approach | journal = Journal of Health Economics | volume = 31 | issue = 1 | pages = 219–30 | date = January 2012 | pmid = 22094013 | doi = 10.1016/j.jhealeco.2011.10.003 | s2cid = 6717295 }}</ref><ref>{{cite journal|vauthors=Finkelstein EA, Fiebelkorn IA, Wang G |title=National medical spending attributable to overweight and obesity: How much, and who's paying |journal=Health Affairs |issue=May |pages= W3–219–W3–226|date=1 January 2003 |volume=22 |url=http://content.healthaffairs.org/cgi/content/full/hlthaff.w3.219v1/DC1 |doi=10.1377/hlthaff.w3.219|pmid=14527256 |url-access=subscription }}</ref><ref>{{cite web|url=https://www.cdc.gov/nccdphp/dnpa/obesity/economic_consequences.htm |title=Obesity and overweight: Economic consequences |publisher=[[Centers for Disease Control and Prevention]] |date=22 May 2007 |access-date=5 September 2007}}</ref> while the cost of obesity in Canada was estimated at CA$2&nbsp;billion in 1997 (2.4% of total health costs).<ref name="CADG2006"/> The total annual direct cost of overweight and obesity in Australia in 2005 was A$21&nbsp;billion. Overweight and obese Australians also received A$35.6&nbsp;billion in government subsidies.<ref name="MJA2009">{{cite journal | vauthors = Colagiuri S, Lee CM, Colagiuri R, Magliano D, Shaw JE, Zimmet PZ, Caterson ID | title = The cost of overweight and obesity in Australia | journal = The Medical Journal of Australia | volume = 192 | issue = 5 | pages = 260–4 | date = March 2010 | pmid = 20201759 | doi =  10.5694/j.1326-5377.2010.tb03503.x| s2cid = 1588787 | url = https://www.mja.com.au/public/issues/192_05_010310/col10841_fm.html | type = Comparative Study | url-access = subscription }}</ref> The estimated range for annual expenditures on diet products is $40&nbsp;billion to $100&nbsp;billion in the US alone.<ref>{{cite news| vauthors = Cummings L |title=The diet business: Banking on failure |work=BBC News |date=5 February 2003 |url= http://news.bbc.co.uk/2/hi/business/2725943.stm |access-date=25 February 2009}}</ref>

[[The Lancet]] Commission on Obesity in 2019 called for a global treaty—modelled on the [[WHO Framework Convention on Tobacco Control]]—committing countries to address obesity and undernutrition, explicitly excluding the food industry from policy development. They estimate the global cost of obesity $2&nbsp;trillion a year, about or 2.8% of world GDP.<ref>{{cite news |title=Public health experts call for global food treaty |url=https://www.ft.com/content/e32dfada-1ffa-11e9-b126-46fc3ad87c65?emailId=5c4ede5258d4740004049132 |access-date=7 March 2019 |newspaper=Financial Times |date=27 January 2019}}</ref>

Obesity prevention programs have been found to reduce the cost of treating obesity-related disease. However, the longer people live, the more medical costs they incur. Researchers, therefore, conclude that reducing obesity may improve the public's health, but it is unlikely to reduce overall health spending.<ref>{{cite journal | vauthors = van Baal PH, Polder JJ, de Wit GA, Hoogenveen RT, Feenstra TL, Boshuizen HC, Engelfriet PM, Brouwer WB | title = Lifetime medical costs of obesity: prevention no cure for increasing health expenditure | journal = PLOS Medicine | volume = 5 | issue = 2 | article-number = e29 | date = February 2008 | pmid = 18254654 | pmc = 2225430 | doi = 10.1371/journal.pmed.0050029 | type = Comparative Study | doi-access = free }}</ref> Sin taxes such as a [[sugary drink tax]] have been implemented in certain countries globally to curb dietary and consumer habits, and as an effort to offset the economic tolls.

[[File:Wide Chair.jpg|thumb|left|upright=1.3|alt=An extra wide chair beside a number of normal sized chairs.|Services accommodate obese people with specialized equipment such as much wider chairs.<ref>{{cite journal | vauthors = Bakewell J |title=Bariatric furniture: Considerations for use |journal=Int J Ther Rehabil |issue=7 |pages=329–33 |year=2007 |url=http://www.ijtr.co.uk/cgi-bin/go.pl/library/article.cgi?uid=23858;article=IJTR_14_7_329_333 |archive-url=https://web.archive.org/web/20111008202913/http://www.ijtr.co.uk/cgi-bin/go.pl/library/article.cgi?uid=23858;article=IJTR_14_7_329_333 |archive-date=8 October 2011 |volume=14 |doi=10.12968/ijtr.2007.14.7.23858 |url-access=subscription }}</ref>]]
Obesity can lead to social stigmatization and disadvantages in employment.<ref name="Puhl_2005"/>{{rp|29}} When compared to their ideal weight counterparts, workers with obesity, on average have higher rates of absenteeism from work and take more disability leave, thus increasing costs for employers and decreasing productivity.<ref>{{cite journal | vauthors = Neovius K, Johansson K, Kark M, Neovius M | title = Obesity status and sick leave: a systematic review | journal = Obesity Reviews | volume = 10 | issue = 1 | pages = 17–27 | date = January 2009 | pmid = 18778315 | doi = 10.1111/j.1467-789X.2008.00521.x | s2cid = 20420379 | type = Review }}</ref> A study examining Duke University employees found that people with a BMI over 40&nbsp;kg/m<sup>2</sup> filed twice as many [[workers' compensation]] claims as those whose BMI was 18.5–24.9&nbsp;kg/m<sup>2</sup>. They also had more than 12&nbsp;times as many lost work days. The most common injuries in this group were due to falls and lifting, thus affecting the lower extremities, wrists or hands, and backs.<ref>{{cite journal | vauthors = Ostbye T, Dement JM, Krause KM | title = Obesity and workers' compensation: results from the Duke Health and Safety Surveillance System | journal = Archives of Internal Medicine | volume = 167 | issue = 8 | pages = 766–73 | date = April 2007 | pmid = 17452538 | doi = 10.1001/archinte.167.8.766 | type = Research Support | doi-access =  }}</ref> The Alabama State Employees' Insurance Board approved a controversial plan to charge obese workers $25 a month for health insurance that would otherwise be free unless they take steps to lose weight and improve their health. These measures started in January 2010 and apply to those state workers whose BMI exceeds 35&nbsp;kg/m<sup>2</sup> and who fail to make improvements in their health after one year. This becomes a Catch 22 position as many insurance companies will refuse to pay for treatment methods for workers living with obesity.<ref>{{cite web|url=https://www.webmd.com/diet/news/20080825/alabama-obesity-penalty-stirs-debate |title=Alabama "Obesity Penalty" Stirs Debate |website=Don Fernandez |access-date=5 April 2009}}</ref>

Some research shows that people with obesity are less likely to be hired for a job and are less likely to be promoted.<ref name=Bias2001/> People with obesity are also paid less than their counterparts who do not live with obesity for an equivalent job; women with obesity on average make 6% less and men with obesity make 3% less.<ref name = "Puhl_2005" />{{rp|30}}

Specific industries, such as the airline, healthcare and food industries, have special concerns. Due to rising rates of obesity, airlines face higher fuel costs and pressures to increase seating width.<ref>{{cite web| vauthors = DiCarlo L |url=https://www.forbes.com/2002/10/24/cx_ld_1024obese.html |title=Why Airlines Can't Cut The Fat |website=Forbes.com |date=24 October 2002 |access-date=23 July 2008}}</ref> In 2000, the extra weight of passengers with obesity cost airlines US$275&nbsp;million.<ref>{{cite journal | vauthors = Dannenberg AL, Burton DC, Jackson RJ | title = Economic and environmental costs of obesity: the impact on airlines | journal = American Journal of Preventive Medicine | volume = 27 | issue = 3 | page = 264 | date = October 2004 | pmid = 15450642 | doi = 10.1016/j.amepre.2004.06.004 | type = Letter | url = https://zenodo.org/record/1258704 }}</ref> The healthcare industry has had to invest in special facilities for handling  patients with class III obesity, including special lifting equipment and [[bariatric ambulance]]s.<ref>{{cite web|url=https://abcnews.go.com/Health/Diet/obese-health-care-bariatric-ambulances/story?id=7981746 |title=Who Should Pay for Obese Health Care? | vauthors = Cox L |publisher=ABC News |date=2 July 2009 |access-date=6 August 2012}}</ref> Costs for restaurants are increased by litigation accusing them of causing obesity.<ref name=Govtrack>{{cite web |url=http://www.govtrack.us/congress/bill.xpd?bill=h109-554 |title=109th U.S. Congress (2005–2006) H.R. 554: 109th U.S. Congress (2005–2006) H.R. 554: Personal Responsibility in Food Consumption Act of 2005 |publisher=GovTrack.us |access-date=24 July 2008 |archive-date=1 November 2008 |archive-url=https://web.archive.org/web/20081101192335/http://www.govtrack.us/congress/bill.xpd?bill=h109-554 }}</ref> In 2005, the US Congress discussed legislation to prevent civil lawsuits against the food industry in relation to obesity; however, it did not become law.<ref name=Govtrack/>

With the [[American Medical Association]]'s 2013 classification of obesity as a chronic disease,<ref name=NYTimes20130618/> it is thought that health insurance companies will more likely pay for obesity treatment, counseling and surgery, and the cost of research and development of adipose treatment pills or gene therapy treatments should be more affordable if insurers help to subsidize their cost.<ref name=WashPost20130620/> The AMA classification is not legally binding, however, so health insurers still have the right to reject coverage for a treatment or procedure.<ref name=WashPost20130620>{{cite news|url=https://www.washingtonpost.com/blogs/innovations/wp/2013/06/20/a-changing-battlefield-in-the-fight-against-fat/ |title=A changing battlefield in the fight against fat | vauthors = Basulto D |date=20 June 2013 |newspaper=The Washington Post |access-date=20 June 2013 |url-status=live |archive-url= https://web.archive.org/web/20140902215705/http://www.washingtonpost.com/blogs/innovations/wp/2013/06/20/a-changing-battlefield-in-the-fight-against-fat/?wpisrc=nl_tech_b |archive-date=2 September 2014 }}</ref>

In 2014, The European Court of Justice ruled that morbid obesity is a disability. The Court said that if an employee's obesity prevents them from "full and effective participation of that person in professional life on an equal basis with other workers", then it shall be considered a disability and that firing someone on such grounds is discriminatory.<ref>{{Cite news|url = https://www.reuters.com/article/eu-courts-obesity-idUSL1N0U20PE20141218|title = Obesity can be deemed a disability at work – EU court|date = 18 December 2014|access-date = 18 December 2014|newspaper = Reuters}}</ref>

In low-income countries, obesity can be a signal of wealth. A 2023 experimental study found that obese individuals in Uganda were more likely to access credit.<ref>{{Cite journal |vauthors = Macchi E |date=2023 |title=Worth Your Weight: Experimental Evidence on the Benefits of Obesity in Low-Income Countries |journal=American Economic Review |language=en |volume=113 |issue=9 |pages=2287–2322 |doi=10.1257/aer.20211879 |pmid=40098923 |pmc=11912229 |hdl=10419/251433 |s2cid=244396815 |issn=0002-8282|hdl-access=free }}</ref>

===Size acceptance===
{{See also|Fat acceptance movement|Social stigma of obesity|Health at Every Size|Fat fetishism}}
[[File:PresidentTaftTelephoneCrop.jpg|thumb|upright=1|[[United States President]] [[William Howard Taft]] was often ridiculed for being overweight.]]
[[File:Wahlkampf_Landtagswahl_NRW_2022_-_Bündnis_90-Die_Grünen_-_Heumarkt_Köln_2022-05-13-4484.jpg|thumb|upright=1|German politician [[Ricarda Lang]] is a victim of fat shaming on the internet.<ref>{{Cite web |url=https://www.stuttgarter-nachrichten.de/inhalt.fat-shaming-im-netz-ricarda-lang-die-angegriffene.98723719-7c97-4469-8e20-27ffb51ac6d6.html |title=Fat Shaming im Netz: Ricarda Lang, die Angegriffene |website=[[stuttgarter-nachrichten.de]] | vauthors = Hanna S |date=January 31, 2022 |access-date=March 25, 2023 |language=de}}</ref>]]

The principal goal of the fat acceptance movement is to decrease discrimination against people who are overweight and obese.<ref>{{cite web|url=http://www.capitalnaafa.org/whatisnaafa.html |title=What is NAAFA |website=[[National Association to Advance Fat Acceptance]] |access-date=17 February 2009 |url-status=usurped |archive-url=https://web.archive.org/web/20090312001218/http://www.capitalnaafa.org/whatisnaafa.html |archive-date=12 March 2009 }}</ref><ref>{{cite web|url=http://www.size-acceptance.org/mission.html |title=ISAA Mission Statement |website=[[International Size Acceptance Association]] |access-date=17 February 2009}}</ref> However, some in the movement are also attempting to challenge the established relationship between obesity and negative health outcomes.<ref name=Pulver2007>{{cite book| vauthors = Pulver A |title=An Imperfect Fit: Obesity, Public Health, and Disability Anti-Discrimination Law |publisher=Social Science Electronic Publishing |year=2007 |doi=10.2139/ssrn.1316106 |ssrn=1316106 |s2cid=153699669 }}</ref>

A number of organizations exist that promote the acceptance of obesity. They have increased in prominence in the latter half of the 20th&nbsp;century.<ref>{{cite journal | vauthors = Neumark-Sztainer D | title = The weight dilemma: a range of philosophical perspectives | journal = International Journal of Obesity and Related Metabolic Disorders | volume = 23 | issue = Suppl 2 | pages = S31–7 | date = March 1999 | pmid = 10340803 | doi = 10.1038/sj.ijo.0800857 | type = Review | doi-access = free }}</ref> The US-based [[National Association to Advance Fat Acceptance]] (NAAFA) was formed in 1969 and describes itself as a civil rights organization dedicated to ending size discrimination.<ref>{{cite web |author=National Association to Advance Fat Acceptance |url=http://www.naafaonline.com/dev2/ |title=We come in all sizes |publisher=NAAFA |year=2008 |access-date=29 July 2008 |archive-date=26 December 2018 |archive-url=https://web.archive.org/web/20181226125112/https://www.naafaonline.com/dev2/%20 }}</ref>

The [[International Size Acceptance Association]] (ISAA) is a [[non-governmental organization]] (NGO) which was founded in 1997. It has more of a global orientation and describes its mission as promoting size acceptance and helping to end weight-based discrimination.<ref>{{cite web|url=http://www.size-acceptance.org/ |title=International Size Acceptance Association – ISAA |website=International Size Acceptance Association |access-date=13 January 2009}}</ref> These groups often argue for the recognition of obesity as a disability under the US [[Americans With Disabilities Act]] (ADA). The American legal system, however, has decided that the potential public health costs exceed the benefits of extending this anti-discrimination law to cover obesity.<ref name=Pulver2007/>

===Industry influence on research===
In 2015, the ''New York Times'' published an article on the [[Global Energy Balance Network]], a nonprofit founded in 2014 that advocated for people to focus on increasing exercise rather than reducing calorie intake to avoid obesity and to be healthy. The organization was founded with at least $1.5M in funding from the [[Coca-Cola Company]], and the company has provided $4M in research funding to the two founding scientists Gregory A. Hand and [[Steven Blair|Steven N. Blair]] since 2008.<ref>{{cite news| vauthors = O'Connor A |title=Coca-Cola Funds Scientists Who Shift Blame for Obesity Away From Bad Diets|url=http://well.blogs.nytimes.com/2015/08/09/coca-cola-funds-scientists-who-shift-blame-for-obesity-away-from-bad-diets/?login=email&mtrref=www.nytimes.com|work=The New York Times|date=9 August 2015}}</ref><ref name=NesleJAMA>{{cite journal | vauthors = Nestle M | title = Food Industry Funding of Nutrition Research: The Relevance of History for Current Debates | journal = JAMA Internal Medicine | volume = 176 | issue = 11 | pages = 1685–1686 | date = November 2016 | pmid = 27618496 | doi = 10.1001/jamainternmed.2016.5400 | s2cid = 29815670 }}</ref>

===Reports===
Many organizations have published reports pertaining to obesity. In 1998, the first US Federal guidelines were published, titled "Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report".<ref>{{cite book |author=((National Heart, Lung, and Blood Institute)) |url=https://www.nhlbi.nih.gov/files/docs/guidelines/ob_gdlns.pdf |title=Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults |publisher=International Medical Publishing, Inc |year=1998 |isbn=978-1-58808-002-8}}</ref> In 2006, the [[Canadian Obesity Network]], now known as [[Obesity Canada]] published the "Canadian Clinical Practice Guidelines (CPG) on the Management and Prevention of Obesity in Adults and Children". This is a comprehensive evidence-based guideline to address the management and prevention of overweight and obesity in adults and children.<ref name="CADG2006" />

In 2004, the United Kingdom [[Royal College of Physicians]], the [[Faculty of Public Health]] and the [[Royal College of Paediatrics and Child Health]] released the report "Storing up Problems", which highlighted the growing problem of obesity in the UK.<ref>{{cite book |title=Storing up problems; the medical case for a slimmer nation |date=11 February 2004 |publisher=Royal College of Physicians |isbn=978-1-86016-200-8 |location=London}}</ref> The same year, the [[British House of Commons|House of Commons]] [[Health Select Committee]] published its "most comprehensive inquiry [...] ever undertaken" into the impact of obesity on health and society in the UK and possible approaches to the problem.<ref name="GB2004">{{cite book |author=Great Britain Parliament House of Commons Health Committee |url=https://publications.parliament.uk/pa/cm200304/cmselect/cmhealth/23/2302.htm |title=Obesity – Volume 1 – HCP 23-I, Third Report of session 2003–04. Report, together with formal minutes |date=May 2004 |publisher=TSO (The Stationery Office) |isbn=978-0-215-01737-6 |location=London |access-date=17 December 2007}}</ref> In 2006, the [[National Institute for Health and Clinical Excellence]] (NICE) issued a guideline on the diagnosis and management of obesity, as well as policy implications for non-healthcare organizations such as local councils.<ref>{{cite web |year=2006 |title=Obesity: guidance on the prevention, identification, assessment and management of overweight and obesity in adults and children |url=https://www.nice.org.uk/nicemedia/pdf/CG43NICEGuideline.pdf |access-date=8 April 2009 |website=National Institute for Health and Clinical Excellence (NICE) |publisher=[[National Health Services]] (NHS)}}</ref> A 2007 report produced by [[Derek Wanless]] for the [[King's Fund]] warned that unless further action was taken, obesity had the capacity to debilitate the [[National Health Service]] financially.<ref>{{cite book |title=Our Future Health Secured? A review of NHS funding and performance |vauthors=Wanless D, Appleby J, Harrison A, Patel D |publisher=The King's Fund |year=2007 |isbn=978-1-85717-562-2 |location=London }}</ref> In 2022 the [[National Institute for Health and Care Research]] (NIHR) published a comprehensive review of research on what [[Local government in England|local authorities]] can do to reduce obesity.<ref name=":6">{{Cite journal |date=19 May 2022 |title=How can local authorities reduce obesity? Insights from NIHR research |url=https://evidence.nihr.ac.uk/how-local-authorities-can-reduce-obesity/ |journal=NIHR Evidence |type=Plain English summary |publisher=National Institute for Health and Care Research |archive-date=1 April 2023 |access-date=24 May 2022 |archive-url=https://web.archive.org/web/20230401161340/https://evidence.nihr.ac.uk/how-local-authorities-can-reduce-obesity/ }}</ref>

The Obesity Policy Action (OPA) framework divides measure into ''upstream'' policies, ''midstream'' policies, and ''downstream'' policies. Upstream policies have to do with changing society, while midstream policies try to alter behaviors believed to contribute to obesity at the individual level, while downstream policies treat currently obese people.<ref>{{cite journal |vauthors=Sacks G, Swinburn B, Lawrence M |date=January 2009 |title=Obesity Policy Action framework and analysis grids for a comprehensive policy approach to reducing obesity |journal=Obesity Reviews |volume=10 |issue=1 |pages=76–86 |doi=10.1111/j.1467-789X.2008.00524.X |pmid=18761640 |doi-access=free |s2cid=30908778|hdl=10536/DRO/DU:30017330 |hdl-access=free }}</ref>

==Childhood obesity==
{{Main|Childhood obesity}}

The healthy BMI range varies with the age and sex of the child. Obesity in children and adolescents is defined as a BMI greater than the 95th&nbsp;[[percentile]].<ref name="cdc.gov">{{cite web|url=https://www.cdc.gov/nccdphp/dnpa/healthyweight/assessing/bmi/childrens_BMI/about_childrens_BMI.htm |title=Healthy Weight: Assessing Your Weight: BMI: About BMI for Children and Teens |publisher=[[Center for disease control and prevention]] |access-date=6 April 2009}}</ref> The reference data that these percentiles are based on is from 1963 to 1994 and thus has not been affected by the recent increases in rates of obesity.<ref name="Flegal KM, Ogden CL, Wei R, Kuczmarski RL, Johnson CL 2001 1086–93">{{cite journal | vauthors = Flegal KM, Ogden CL, Wei R, Kuczmarski RL, Johnson CL | title = Prevalence of overweight in US children: comparison of US growth charts from the Centers for Disease Control and Prevention with other reference values for body mass index | journal = The American Journal of Clinical Nutrition | volume = 73 | issue = 6 | pages = 1086–93 | date = June 2001 | pmid = 11382664 | doi = 10.1093/ajcn/73.6.1086 | doi-access = free }}</ref> Childhood obesity has reached epidemic proportions in the 21st&nbsp;century, with rising rates in both the developed and the developing world. Rates of obesity in Canadian boys have increased from 11% in the 1980s to over 30% in the 1990s, while during this same time period rates increased from 4 to 14% in Brazilian children.<ref name=flynn2006/> In the UK, there were 60% more obese children in 2005 compared to 1989.<ref>{{cite journal | vauthors = Lawrence J | title = Childhood obesity | journal = British Journal of Perioperative Nursing | volume = 15 | issue = 2 | pages = 84, 86–84, 90 | date = February 2005 | pmid = 15736809 | doi = 10.1177/175045890501500204 | s2cid = 31102802 }}</ref> In the US, the percentage of overweight and obese children increased to 16% in 2008, a 300% increase over the prior 30 years.<ref>{{Cite journal| vauthors = Brownback S |date=January 2008|title=Confronting Childhood Obesity|journal=The Annals of the American Academy of Political and Social Science|volume=615|issue=1|pages=219–221|doi=10.1177/0002716207308894|s2cid=144317779|issn=0002-7162}}</ref>

As with obesity in adults, many factors contribute to the rising rates of childhood obesity. Changing diet and decreasing physical activity are believed to be the two most important causes for the recent increase in the incidence of child obesity.<ref>{{cite journal | vauthors = Dollman J, Norton K, Norton L | title = Evidence for secular trends in children's physical activity behaviour | journal = British Journal of Sports Medicine | volume = 39 | issue = 12 | pages = 892–7; discussion 897 | date = December 2005 | pmid = 16306494 | pmc = 1725088 | doi = 10.1136/bjsm.2004.016675 | type = Review }}</ref> [[Food marketing toward children|Advertising of unhealthy foods to children]] also contributes, as it increases their consumption of the product.<ref>{{cite journal | vauthors = Russell SJ, Croker H, Viner RM | title = The effect of screen advertising on children's dietary intake: A systematic review and meta-analysis | journal = Obesity Reviews | volume = 20 | issue = 4 | pages = 554–568 | date = April 2019 | pmid = 30576057 | pmc = 6446725 | doi = 10.1111/obr.12812 }}</ref> Antibiotics in the first 6 months of life have been associated with excess weight at age seven to twelve years of age.<ref name=Cox2015>{{cite journal | vauthors = Cox LM, Blaser MJ | title = Antibiotics in early life and obesity | journal = Nature Reviews. Endocrinology | volume = 11 | issue = 3 | pages = 182–190 | date = March 2015 | pmid = 25488483 | pmc = 4487629 | doi = 10.1038/nrendo.2014.210 }}</ref> Because childhood obesity often persists into adulthood and is associated with numerous chronic illnesses, children who are obese are often tested for [[hypertension]], [[diabetes]], [[hyperlipidemia]], and [[fatty liver disease]].<ref name=CADG2006/>

Treatments used in children are primarily lifestyle interventions and behavioral techniques, although efforts to increase activity in children have had little success.<ref name="pmid23044984">{{cite journal | vauthors = Metcalf B, Henley W, Wilkin T | title = Effectiveness of intervention on physical activity of children: systematic review and meta-analysis of controlled trials with objectively measured outcomes (EarlyBird 54) | journal = BMJ | volume = 345 | article-number = e5888 | date = September 2012 | pmid = 23044984 | doi = 10.1136/bmj.e5888 | hdl-access = free | doi-access = free | hdl = 10871/11391 | type = Review, Meta-analysis }}</ref> In the United States, medications are not FDA approved for use in this age group.<ref name="flynn2006">{{cite journal | vauthors = Flynn MA, McNeil DA, Maloff B, Mutasingwa D, Wu M, Ford C, Tough SC | title = Reducing obesity and related chronic disease risk in children and youth: a synthesis of evidence with 'best practice' recommendations | journal = Obesity Reviews | volume = 7 | issue = Suppl 1 | pages = 7–66 | date = February 2006 | pmid = 16371076 | doi = 10.1111/j.1467-789X.2006.00242.x | type = Review | s2cid = 5992031 | doi-access =  }}</ref> Brief weight management interventions in [[primary care]] (e.g. delivered by a physician or nurse practitioner) have only a marginal positive effect in reducing childhood overweight or obesity.<ref>{{cite journal | vauthors = Sim LA, Lebow J, Wang Z, Koball A, Murad MH | title = Brief Primary Care Obesity Interventions: A Meta-analysis | journal = Pediatrics | volume = 138 | issue = 4 | article-number = e20160149 | date = October 2016 | pmid = 27621413 | doi = 10.1542/peds.2016-0149 | s2cid = 26039769 | doi-access = free }}</ref> Multi-component behaviour change interventions that include changes to dietary and physical activity may reduce BMI in the short term in children aged 6 to 11 years, although the benefits are small and quality of evidence is low.<ref>{{cite journal | vauthors = Mead E, Brown T, Rees K, Azevedo LB, Whittaker V, Jones D, Olajide J, Mainardi GM, Corpeleijn E, O'Malley C, Beardsmore E, Al-Khudairy L, Baur L, Metzendorf MI, Demaio A, Ells LJ | title = Diet, physical activity and behavioural interventions for the treatment of overweight or obese children from the age of 6 to 11 years | journal = The Cochrane Database of Systematic Reviews | volume = 2017 | issue = 6 | article-number = CD012651 | date = June 2017 | pmid = 28639319 | pmc = 6481885 | doi = 10.1002/14651858.CD012651 }}</ref>

==Statistics==
The CDC reported that this prevalence of obesity among U.S. adults 20 and over was 41.9% during 2017–March 2020  in which during the same time, the prevalence of severe obesity among U.S. adults was 9.2%.<ref>{{Cite web |last=CDC |date=2025-03-25 |title=Adult Obesity Facts |url=https://www.cdc.gov/obesity/adult-obesity-facts/index.html |access-date=2025-11-03 |website=Obesity |language=en-us}}</ref>  The prevalence of obesity was lowest among non-Hispanic Asian adults (17.4%) compared with non-Hispanic white (42.2%), non-Hispanic black (49.6%), and Hispanic (44.8%) adults.<ref>{{Cite web |date=2020-06-26 |title=Products - Data Briefs - Number 360 - February 2020 |url=https://www.cdc.gov/nchs/products/databriefs/db360.htm |access-date=2025-11-03 |website=www.cdc.gov |language=en-us}}</ref>
[[File:Statistics of obesity in 2017-2018.png|alt=|thumb|Obesity statistics in 2017-2018]]

==Other animals==
{{Main|Obesity in pets}}

Obesity in pets is common in many countries. In the United States, 23–41% of dogs are overweight, and about 5.1% are obese.<ref name=Lund2006>{{cite journal| vauthors = Lund EM |title=Prevalence and Risk Factors for Obesity in Adult Dogs from Private US Veterinary Practices |journal=Intern J Appl Res Vet Med |volume=4 |issue=2 |pages=177–86 |year=2006 |url=http://www.jarvm.com/articles/Vol4Iss2/Lund.pdf}}</ref> The rate of obesity in cats was slightly higher at 6.4%.<ref name=Lund2006/> In Australia, the rate of obesity among dogs in a veterinary setting has been found to be 7.6%.<ref>{{cite journal | vauthors = McGreevy PD, Thomson PC, Pride C, Fawcett A, Grassi T, Jones B | title = Prevalence of obesity in dogs examined by Australian veterinary practices and the risk factors involved | journal = The Veterinary Record | volume = 156 | issue = 22 | pages = 695–702 | date = May 2005 | pmid = 15923551 | doi = 10.1136/vr.156.22.695 | s2cid = 36725298 }}</ref> The risk of obesity in dogs is related to whether or not their owners are obese; however, there is no similar correlation between cats and their owners.<ref>{{cite journal | vauthors = Nijland ML, Stam F, Seidell JC | title = Overweight in dogs, but not in cats, is related to overweight in their owners | journal = Public Health Nutrition | volume = 13 | issue = 1 | pages = 102–6 | date = January 2010 | pmid = 19545467 | doi = 10.1017/S136898000999022X | doi-access = free }}</ref>

==See also==
* [[Portal-visceral hypothesis]]
* [[Anti-Obesity Day]]
* [[Health effects of ultra-processed foods]]

==References==
=== Citations ===
{{Reflist}}

==Further reading==
<!-- Please only include material which addresses obesity in general, rather than specific aspects, or related topics -->
{{offline|med}}
{{Refbegin|30em}}
* {{cite journal |title=Obesity 2015 | quote = Series from the Lancet journals |url=http://www.thelancet.com/series/obesity-2015 |journal=[[The Lancet]] |year=2015}}
* {{cite book | vauthors = Jebb S, Wells J | chapter = Measuring body composition in adults and children | veditors = Kopelman PG, Caterson ID, Stock MJ, Dietz WH |title=Clinical obesity in adults and children: In Adults and Children |publisher=Blackwell Publishing |year=2005 |pages=[https://archive.org/details/clinicalobesityi02edunse/page/12 12–28] |isbn=978-1-4051-1672-5 | chapter-url = https://archive.org/details/clinicalobesityi02edunse/page/12 }}
* {{cite book |author=(([[National Heart, Lung, and Blood Institute]] (NHLBI))) |title=Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults |publisher=International Medical Publishing, Inc |year=1998 |isbn=978-1-58808-002-8 |url=https://www.nhlbi.nih.gov/files/docs/guidelines/ob_gdlns.pdf }}
* {{cite web |url=https://www.nice.org.uk/nicemedia/pdf/CG43NICEGuideline.pdf |title=Obesity: guidance on the prevention, identification, assessment and management of overweight and obesity in adults and children |publisher=[[National Health Services]] (NHS) |year=2006 |website=[[National Institute for Health and Clinical Excellence]](NICE) |access-date=8 April 2009 }}
* {{cite book |author=World Health Organization (WHO) |title=Technical report series 894: Obesity: Preventing and managing the global epidemic |location=Geneva |publisher=World Health Organization |year=2000 |url=http://whqlibdoc.who.int/trs/WHO_TRS_894_(part1).pdf |isbn=978-92-4-120894-9 |access-date=10 May 2006 |archive-url=https://web.archive.org/web/20150501075305/http://whqlibdoc.who.int/trs/WHO_TRS_894_(part1).pdf |archive-date=1 May 2015 }}
{{Refend}}

== External links ==
* {{wikiquote-inline}}
* [https://www.who.int/mediacentre/factsheets/fs311/en/ WHO fact sheet on obesity and overweight]

{{Medical condition classification and resources
 |DiseasesDB  = 9099
 |ICD11       = {{ICD11|5B81|149403041}}
 |ICD10       = {{ICD10|E|66| |e|65}}
 |ICD9        = {{ICD9|278}}
 |MedlinePlus = 007297
 |OMIM        = 601665
 |eMedicineSubj  = med
 |eMedicineTopic = 1653
 |MeshName    = Obesity
 |MeshNumber  = C23.888.144.699.500
}}
{{Subject bar |portal1= Medicine |commons= y |commons-search= Category:Obesity|n= y |wikt= y|b= y |q= y |s= y |v= n |voy= n }}
{{Obesity}}
{{Authority control}}

[[Category:Obesity| ]]
[[Category:Bariatrics]]
[[Category:Body shape]]
[[Category:Nutrition]]