View source for Fructose

{{short description|Simple ketonic monosaccharide found in many plants}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 477167440
| Name = {{sm|d}}-Fructose
| ImageClassL1 = skin-invert-image
| ImageFileL1 = Skeletal Structure of Cyclic D-Fructose.svg
| ImageCaptionL1 = {{sm|d}}-Fructofuranose
| ImageSizeL1 = 150px
| ImageClassR1 = skin-invert-image
| ImageFileR1 = D-Fructose.svg
| ImageSizeR1 = 60px
| ImageCaptionR1 = {{sm|d}}-Fructose (open-chain form)
| ImageClass2 = skin-invert-image
| ImageFile2 = Beta-D-Fructofuranose.svg
| ImageName2 = β-{{sm|d}}-fructose structure
| ImageCaption2 = [[Haworth projection]] of β-{{sm|d}}-fructofuranose
| ImageFileL3 = Beta-D-fructofuranose-from-xtal-view-1-3D-bs-17.png
| ImageClassL3 = bg-transparent
| ImageCaptionL3 = [[Ball-and-stick model]] of β-{{sm|d}}-fructo[[furanose]]
| ImageFileR3 = Beta-D-fructopyranose-from-xtal-view-2-3D-bs-17.png
| ImageClassR3 = bg-transparent
| ImageCaptionR3 = Ball-and-stick model of β-{{sm|d}}-fructo[[pyranose]]
| IUPACName = <small>D</small>-''arabino''-Hex-2-ulose<ref>{{cite web | url=https://iupac.qmul.ac.uk/2carb/10.html | title=2-Carb-10 | access-date=2023-06-18 | archive-date=2023-06-18 | archive-url=https://web.archive.org/web/20230618145008/https://iupac.qmul.ac.uk/2carb/10.html | url-status=live }}</ref>
|SystematicName=(3''S'',4''R'',5''R'')-1,3,4,5,6-Pentahydroxyhexan-2-one
| OtherNames = Fruit sugar,<ref>{{cite web|url=http://mw4.m-w.com/dictionary/fructose|title=Fructose | publisher= Merriam-Webster | website= m-w.com |access-date=10 December 2014| url-status= dead|archive-url=https://web.archive.org/web/20110419073934/http://mw4.m-w.com/dictionary/fructose|archive-date=19 April 2011}}</ref> levulose,<ref>Levulose comes from the Latin word ''laevus'', "left"; levulose is the old word for the most occurring [[isomer]] of fructose. D-fructose rotates plane-polarised light to the left, hence the name.{{cite web |url=http://www.monashscientific.com.au/Levulose.htm |title=Levulose |access-date=2010-01-28 |url-status=live |archive-url= https://web.archive.org/web/20091008032809/http://www.monashscientific.com.au/Levulose.htm |archive-date=2009-10-08 }}.</ref> {{sm|d}}-fructofuranose, {{sm|d}}-fructose, {{sm|d}}-arabino-hexulose
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 388775
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 6YSS42VSEV
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 604608
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C02336
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C6H12O6/c7-1-3-4(9)5(10)6(11,2-8)12-3/h3-5,7-11H,1-2H2/t3-,4-,5+,6-/m1/s1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = RFSUNEUAIZKAJO-ARQDHWQXSA-N
| CASNo = 57-48-7
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 5984
| EC_number = 200-333-3
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 48095
| SMILES = O[C@H]1[C@H](O)[C@H](O[C@]1(O)CO)CO
 }}

| Section2 = {{Chembox Properties
| C=6 | H=12 | O=6
| Density = 1.694 g/cm<sup>3</sup>
| Solubility = ~4000 g/L (25 °C)
| MeltingPtC = 103
| MagSus = −102.60×10<sup>−6</sup> cm<sup>3</sup>/mol
 }}

| Section4 = {{Chembox Thermochemistry
| Thermochemistry_ref =
| HeatCapacity = 
| Entropy = 
| DeltaHf = 
| DeltaGf =
| DeltaHc ={{cvt|675.6|kcal/mol|kJ/mol}}<ref name=CRC>{{cite book| title= [[CRC Handbook of Chemistry and Physics]]| edition= 49th | year= 1968–69| page= D-186| isbn= }}</ref> ([[Higher heating value]])}}

| Section6 = {{Chembox Pharmacology
| ATCCode_prefix = V06
| ATCCode_suffix = DC02
}}

| Section7 = {{Chembox Hazards
| LD50 = 15000 mg/kg (intravenous, rabbit)<ref>{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/#tab/sidsrcname=ChemIDplus&query=57-48-7&input_type=text|title=ChemIDplus – 57-48-7 – BJHIKXHVCXFQLS-UYFOZJQFSA-N – Fructose [USP:JAN] – Similar structures search, synonyms, formulas, resource links, and other chemical information.| first= Michael |last= Chambers|publisher= US National Institutes of Health| website= chem.sis.nlm.nih.gov |access-date=10 December 2014|url-status=live|archive-url= https://web.archive.org/web/20141210194215/https://chem.nlm.nih.gov/chemidplus/rn/57-48-7 |archive-date=10 December 2014}}</ref>
 }}
}}

'''Fructose''' ({{IPAc-en|'|f|r|V|k|t|ou|s|,_|-|ou|z}}), or '''fruit sugar''', is a common [[monosaccharide]], i.e. a simple sugar. It is classified as a reducing [[hexose]], more specifically a [[Ketose|ketonic]] [[monosaccharide|simple sugar]] found in many plants, where it is often bonded to [[glucose]] to form the [[disaccharide]] [[sucrose]]. In terms of structure, it is a C-4 [[epimer]] of glucose.  A white, water-soluble solid,It is one of the three dietary monosaccharides, along with [[glucose]] and [[galactose]].<ref name="Ullmann"/>
Fructose is found in [[honey]], tree and vine fruits, flowers, [[Berry|berries]], and most [[List of root vegetables|root vegetables]].

==History==
Fructose was discovered by French chemist [[Augustin-Pierre Dubrunfaut]] in 1847.<ref>{{cite journal| last= Dubrunfaut |year= 1847| url= https://books.google.com/books?id=PJ45AAAAcAAJ&pg=PA169 |title= Sur une propriété analytique des fermentations alcoolique et lactique, et sur leur application à l'étude des sucres| archive-url= https://web.archive.org/web/20140627013828/http://books.google.com/books?id=PJ45AAAAcAAJ&pg=PA169 |archive-date= 2014-06-27| trans-title= On an analytic property of alcoholic and lactic fermentations, and on their application to the study of sugars| language= fr| journal= Annales de Chimie et de Physique| volume= 21| pages= 169–178}}  On page 174, Dubrunfaut relates the discovery and properties of fructose.</ref><ref>{{cite journal |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/food.19740180423 |last=Fruton |first=J. S. |title=Molecules and Life – Historical Essays on the Interplay of Chemistry and Biology |journal=Molecular Nutrition & Food Research |volume=18 |issue=4 |date=1974 |publisher=Wiley-Interscience |place=New York |doi=10.1002/food.19740180423 |access-date=2021-02-05 |archive-date=2021-02-28 |archive-url=https://web.archive.org/web/20210228060441/https://onlinelibrary.wiley.com/doi/abs/10.1002/food.19740180423 |url-status=live |url-access=subscription }}</ref> The name "fructose" was coined in 1857 by the English chemist [[William Allen Miller]].<ref name="Miller">{{cite book | first= William Allen |last= Miller| title=Elements of Chemistry: Theoretical and Practical| chapter= Part III. Organic Chemistry| publisher=John W. Parker and son| place= London |date=1857|url=https://archive.org/details/elementschemist03millgoog|pages= 52, [https://archive.org/details/elementschemist03millgoog/page/n669 57]}}</ref> Pure, dry fructose is a sweet, white, odorless, crystalline solid, and is the most water-soluble of all the sugars.<ref Name=Hyvonen&Koivistoinen1982>{{cite book |year=1982 |author1= Hyvonen, L. |author2= Koivistoinen, P |name-list-style=amp |chapter=Fructose in Food Systems |editor1=Birch, G.G. |editor2=Parker, K.J |title=Nutritive Sweeteners |pages=133–144 |place=London & New Jersey |publisher=Applied Science Publishers |isbn=978-0-85334-997-6 }}</ref>

== Etymology ==
The word "fructose" was coined in 1857 from the Latin for ''fructus'' (fruit) and the generic chemical suffix for sugars, ''[[-ose]]''.<ref name=Miller/><ref name="oed">{{cite web|title=Fructose. Origin and meaning of fructose|publisher=Online Etymology Dictionary, Douglas Harper|url=https://www.etymonline.com/word/fructose|date=2017|access-date=24 December 2017|language=en|url-status=live|archive-url=https://web.archive.org/web/20171225092022/https://www.etymonline.com/word/fructose|archive-date=25 December 2017}}</ref> It is also called fruit sugar and levulose or laevulose, due to its ability to rotate plane polarised light in a [[Optical rotation|laevorotary]] fashion (anti-clockwise/to the left) when a beam is shone through it in solution. Likewise, [[Glucose|dextrose]] (an isomer of glucose) is given its name due to its ability to rotate plane polarised light in a [[Optical rotation|dextrorotary]] fashion (clockwise/to the right).<ref name=oed/>

== Chemical structure ==
[[File:Isomeric forms of fructose.svg|thumb|375px|left|Relationship between the [[Open-chain|acyclic]] and the cyclic ([[hemiketal]]) isomers of fructose]]<!--ratio may need tweaking but axial vs equatorial has no meaning in Haworth projections-->
[[File:DL-Fructose num.svg|thumb|255px|upright=1.5|{{sm|d}}- and {{sm|l}}-isomers of fructose (open-chain form)]]

Fructose adopts both cyclic six- and five-membered structure,  The six membered ring can exist as either the β-{{sm|d}}-fructopyranose and α-{{sm|d}}-fructopyranose.  The five-membered rings exists as either of two isomers β-{{sm|d}}-fructo[[furanose]] and α-{{sm|d}}-fructofuranose.  Additionally, an acyclic (open-chain) form exists: ''keto''-{{sm|d}}-fructose.<ref>{{cite journal |last1=Shi |first1=Kemeng |last2=Pedersen |first2=Christian Marcus |last3=Guo |first3=Zhaohui |last4=Li |first4=Yanqiu |last5=Zheng |first5=Hongyan |last6=Qiao |first6=Yan |last7=Hu |first7=Tuoping |last8=Wang |first8=Yingxiong |title=NMR studies of the tautomer distributions of d‑fructose in lower alcohols/DMSO‑d6 |journal=Journal of Molecular Liquids |date=1 December 2018 |volume=271 |pages=926–932 |doi=10.1016/j.molliq.2018.09.067 |s2cid=104659783 |url=https://doi.org/10.1016/j.molliq.2018.09.067 |access-date=24 February 2021 |archive-date=28 February 2021 |archive-url=https://web.archive.org/web/20210228070418/https://linkinghub.elsevier.com/retrieve/pii/S0167732218329805 |url-status=live |url-access=subscription }}</ref><ref>{{cite journal |last1=Schneider |first1=Bernd |last2=Lichtenthaler |first2=Frieder W. |last3=Steinle |first3=Georg |last4=Schiweck |first4=Hubert |title=Studies on Ketoses, 1 Distribution of Furanoid and Pyranoid Tautomers of D-Fructose in Water, Dimethyl Sulfoxide, and Pyridine via <sup>1</sup>H NMR Intensities of Anomeric Hydroxy Groups in [D6]DMSO |journal=Liebigs Annalen der Chemie |date=22 December 1985 |volume=1985 |issue=12 |pages=2443–2453 |doi=10.1002/jlac.198519851213 |url=https://doi.org/10.1002/jlac.198519851213 |access-date=24 February 2021 |archive-date=24 February 2022 |archive-url=https://web.archive.org/web/20220224181718/https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/jlac.198519851213 |url-status=live |url-access=subscription }}</ref>  At 70% and 22% respectively, fructopyranose and fructofuranose are the dominant species in aqueous solution.<ref>{{cite journal |last1=Funcke |first1=Werner |last2=von Sonntag |first2=Clemens |last3=Triantaphylides |first3=Christian |title=Detection of the open-chain forms of d-fructose and L-sorbose in aqueous solution by using 13C-n.m.r. spectroscopy |journal=Carbohydrate Research |date=October 1979 |volume=75 |pages=305–309 |doi=10.1016/S0008-6215(00)84649-2 |url=https://doi.org/10.1016/S0008-6215(00)84649-2 |access-date=24 February 2021 |archive-date=28 February 2021 |archive-url=https://web.archive.org/web/20210228070325/https://linkinghub.elsevier.com/retrieve/pii/S0008621500846492 |url-status=live |url-access=subscription }}</ref>

===Chemical reactions===
==== Fructose and fermentation ====
Fructose may be anaerobically [[Ethanol fermentation|fermented]] by [[yeast]] and [[bacteria]].<ref>{{cite book | last=McWilliams | first=Margaret | title=Foods: Experimental Perspectives, 4th Edition | isbn=978-0-13-021282-5 | year=2001 | publisher=Prentice Hall | url=https://archive.org/details/foodsexperimenta00mcwi }}</ref> Yeast enzymes convert sugar ([[sucrose]], [[glucose]], and fructose, but not [[lactose]]) to [[ethanol]] and [[carbon dioxide]].<ref>{{cite web|last=Keusch |first=P |title=Yeast and Sugar- the Chemistry must be right |url=http://www.chemie.uni-regensburg.de/Organische_Chemie/Didaktik/Keusch/D-fermentation_sugar-e.htm |url-status=dead |archive-url=https://web.archive.org/web/20101220064304/http://www.chemie.uni-regensburg.de/Organische_Chemie/Didaktik/Keusch/D-fermentation_sugar-e.htm |archive-date=December 20, 2010 }}</ref> Some of the carbon dioxide produced during fermentation will remain dissolved in water, where it will reach equilibrium with [[carbonic acid]]. The dissolved carbon dioxide and carbonic acid produce the carbonation in some [[fermented beverage]]s, such as [[champagne]].

==== Fructose and Maillard reaction ====
Fructose undergoes the [[Maillard reaction]], non-enzymatic browning, with [[amino acid]]s. Because fructose exists to a greater extent in the open-chain form than does glucose, the initial stages of the Maillard reaction occur more rapidly than with glucose. Therefore, fructose has potential to contribute to changes in food [[palatability]], as well as other nutritional effects, such as excessive browning, volume and tenderness reduction during cake preparation, and formation of [[mutagenic]] compounds.<ref>{{cite journal | last=Dills | first=WL | title=Protein fructosylation: Fructose and the Maillard reaction | year=1993 | journal=Journal of Clinical Nutrition | volume=58 | issue=5 Suppl | pages=779–787| doi=10.1093/ajcn/58.5.779S | pmid=8213610 | doi-access=free }}</ref>
==== Dehydration ====
Fructose can be dehydrated to give [[hydroxymethylfurfural]] ("HMF", {{chem|C|6|H|6|O|3}}), which can be processed into liquid [[2,5-Dimethylfuran|dimethylfuran]] ({{chem|C|6|H|8|O}}).
This conversion has long been proposed, not implemented, as a route to [[green fuel]]s.<ref>{{cite journal | doi = 10.1021/cr068360d | volume = 106 | title = Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering | date = September 2006 | journal = Chem. Rev. | pages = 4044–98 | last1 = Huber | first1 = GW | last2 = Iborra | first2 = S | last3 = Corma | first3 = A | issue = 9 | pmid = 16967928}}</ref>

== Physical and functional properties ==

=== Sweetness of fructose ===
{{See also|Sweetness#Examples of sweet substances}}
The primary reason that fructose is used commercially in foods and beverages, besides its low cost, is its high relative sweetness. It is the sweetest of all naturally occurring [[carbohydrate]]s. The relative sweetness of fructose has been reported in the range of 1.2–1.8 times that of sucrose.<ref name=Hanover>{{cite journal|last1=Hanover|first1=L. M.| last2= White| first2=J. S.|title=Manufacturing, composition, and applications of fructose |journal= [[The American Journal of Clinical Nutrition]]| via= nutrition.org |date=1 November 1993 |volume= 58 |issue=5 |pages= 724S–732S| url=http://ajcn.nutrition.org/content/58/5/724S.abstract|access-date=7 February 2017| language=en |issn= 0002-9165 |url-status= live |archive-url= https://web.archive.org/web/20160414002156/http://ajcn.nutrition.org/content/58/5/724S.abstract|archive-date=14 April 2016|doi=10.1093/ajcn/58.5.724S|pmid=8213603|doi-access=free}}</ref><ref name= "Oregon State University">{{cite web| publisher= Oregon State University| title= Sugar Sweetness| url= http://food.oregonstate.edu/sugar/sweet.html |archiveurl= https://web.archive.org/web/20080516050325/http://food.oregonstate.edu/sugar/sweet.html| website= food.oregonstate.edu |archivedate=May 16, 2008 |accessdate=7 February 2017}}</ref><ref name="Kirk-Othmer">{{cite book| last1= Lee|first1=Thomas D.| chapter= Sweeteners| title= Kirk-Othmer Encyclopedia of Chemical Technology|date=1 January 2000| doi= 10.1002/0471238961.19230505120505.a01.pub2 |language= en|isbn=978-0471238966}}</ref><ref>{{cite journal |last1=Jana| first1=A.H. |last2=Joshi |first2= N.S.S.| title= Sweeteners for frozen [desserts] success – a review |journal= [[Australian Journal of Dairy Technology]] |date=November 1994|volume=49|url=http://agris.fao.org/agris-search/search.do?recordID=AU9500465|access-date=7 February 2017 |url-status= live| archive-url=https://web.archive.org/web/20170208033252/http://agris.fao.org/agris-search/search.do?recordID=AU9500465|archive-date=8 February 2017}}</ref> However, it is the 6-membered ring form of fructose that is sweeter; the 5-membered ring form tastes about the same as usual table sugar.  Warming fructose leads to formation of the 5-membered ring form.<ref>{{cite book | title=Taste Chemistry| last=Shallenberger| first=R.S.| year=1994| publisher=Chapman and Hall | isbn=978-0-7514-0150-9}}</ref> Therefore, the relative sweetness decreases with increasing temperature. However, it has been observed that the absolute sweetness of fructose is identical at 5&nbsp;°C as 50&nbsp;°C and thus the relative sweetness to sucrose is not due to [[anomeric]] distribution but a decrease in the absolute sweetness of sucrose at higher temperatures.<ref name="Kirk-Othmer"/>

[[File:Relativesweetness.svg|thumb|center|400px|Relative sweetness of sugars and sweeteners]]

The sweetness of fructose is perceived earlier than that of sucrose or glucose, and the taste sensation reaches a peak (higher than that of sucrose), and diminishes more quickly than that of sucrose. Fructose can also enhance other flavors in the system.<ref name=Hanover /><ref name="Kirk-Othmer"/>

Fructose exhibits a sweetness synergy effect when used in combination with other sweeteners. The relative sweetness of fructose blended with sucrose, aspartame, or saccharin is perceived to be greater than the sweetness calculated from individual components.<ref name=Nabors>{{cite book | last=Nabors  | first=LO | title =American Sweeteners | year=2001 | pages=374–375}}</ref><ref name="Kirk-Othmer"/>

=== Fructose solubility and crystallization ===
Fructose has higher water solubility than other sugars, as well as other sugar alcohols. Fructose is, therefore, difficult to crystallize from an aqueous solution.<ref name=Hanover /> Sugar mixes containing fructose, such as candies, are softer than those containing other sugars because of the greater solubility of fructose.<ref>{{cite book| title=Foods: Experimental Perspectives, 4th Edition| last=McWilliams| first=Margaret| year=2001| publisher=Upper Saddle River, NJ : Prentice Hall| isbn=978-0-13-021282-5| url=https://archive.org/details/foodsexperimenta00mcwi}}</ref>

=== Fructose hygroscopicity and humectancy ===
Fructose is quicker to absorb moisture and slower to release it to the environment than sucrose, glucose, or other nutritive sweeteners.<ref name=Nabors /> Fructose is an excellent humectant and retains moisture for a long period of time even at low [[relative humidity]] (RH). Therefore, fructose can contribute a more palatable texture, and longer shelf life to the food products in which it is used.<ref name=Hanover />

=== Freezing point ===
Fructose has a greater effect on freezing point depression than disaccharides or oligosaccharides, which may protect the integrity of cell walls of fruit by reducing ice crystal formation. However, this characteristic may be undesirable in soft-serve or hard-frozen dairy desserts.<ref name=Hanover />

=== Fructose and starch functionality in food systems ===
Fructose increases starch viscosity more rapidly and achieves a higher final viscosity than sucrose because fructose lowers the temperature required during [[starch gelatinization|gelatinizing of starch]], causing a greater final viscosity.<ref>{{cite journal | last=White | first=DC |author2=Lauer GN | title=Predicting gelatinization temperature of starch/sweetener system for cake formulation by differential scanning calorimetry I. Development of a model | year=1990 | journal=Cereal Foods World | volume=35 | pages=728–731}}</ref>

Although some artificial sweeteners are not suitable for home baking, many traditional recipes use fructose.<ref>{{cite book|title=New Good Food: Essential Ingredients for Cooking and Eating Well. Diet and Nutrition Series; pages 249–51|author=Margaret M. Wittenberg|publisher=Ten Speed Press|year=2007|isbn=978-1580087506|url=https://archive.org/details/isbn_9781580087506|url-access=registration|page=[https://archive.org/details/isbn_9781580087506/page/249 249]|quote=fructose traditional baking.}}</ref>

==Sources ==
[[File:Table fructose.JPG|thumb|Crystalline fructose]]
===Commercial production===
Fructose is produced on an industrial scale from three precursors: starch, sucrose, and [[inulin]]. 
Sucrose is an [[organic compound]] with one molecule of glucose [[Covalent bond|covalently]] linked to one molecule of fructose. All forms of fructose, including those found in fruits and juices, are commonly added to foods and drinks for [[palatability]] and [[taste]] enhancement, and for browning of some foods, such as baked goods.
<ref name="Ullmann"/>
Fructose is found in [[honey]], tree and vine fruits, flowers, [[Berry|berries]], and most [[List of root vegetables|root vegetables]].

Starch is hydrolyzed to glucose, which is converted to fructose by the enzyme [[glucose isomerase]]. This mixture is [[high-fructose corn syrup]]. At 60 °C, the conversion gives a 1:1 mixture of glucose and fructose.  Sucrose is [[hydrolysis|hydrolyzed]] to give its monomeric precursors glucose and fructose.  Inulin  is also converted to fructose on a commercial scale. As of 2004, about 240,000 [[tonne]]s of crystalline fructose were being produced annually.<ref name="Ullmann">{{cite book |last1=Wach |first1=Wolfgang |title=Ullmann's Encyclopedia of Industrial Chemistry |chapter=Fructose |date=2004 |doi=10.1002/14356007.a12_047.pub2 |isbn=978-3-527-30385-4 }}</ref>Commercially, [[maize]] is a major source of starch. [[Sugar cane]] and [[sugar beet]]s are sources of sucrose is a [[Chemical compound|compound]] with one molecule of glucose [[Covalent bond|covalently]] linked to one molecule of fructose. Inulin is found in [[chicory]],  

All forms of fructose, including those found in fruits and juices, are commonly added to foods and drinks for [[palatability]] and [[taste]] enhancement, and for browning of some foods, such as baked goods.

===Natural sources===
Natural sources of fructose include fruits, vegetables (including sugar cane), and honey.<ref>{{cite journal | last=Park | first=KY |author2=Yetley AE | title=Intakes and food sources of fructose in the United States | year = 1993 | volume = 58 | issue=5 Suppl | pages = 737S–747S | journal=American Journal of Clinical Nutrition | pmid=8213605| doi=10.1093/ajcn/58.5.737S | doi-access=free }}</ref> Fructose is often further concentrated from these sources. The highest dietary sources of fructose, besides pure crystalline fructose, are foods containing [[white sugar]] (sucrose), [[high-fructose corn syrup]], [[agave nectar]], [[honey]], [[molasses]], [[maple syrup]], fruit and fruit [[juice]]s, as these have the highest percentages of fructose (including fructose in sucrose) per serving compared to other common foods and ingredients. Fructose exists in foods either as a free [[monosaccharide]] or bound to glucose as sucrose, a [[disaccharide]]. Fructose, glucose, and sucrose may all be present in food; however, different foods will have varying levels of each of these three sugars.

The sugar contents of common fruits and vegetables are presented in Table 1. In general, in foods that contain free fructose, the ratio of fructose to glucose is approximately 1:1; that is, foods with fructose usually contain about an equal amount of free glucose. A value that is above 1 indicates a higher proportion of fructose to glucose and below 1 a lower proportion. Some fruits have larger proportions of fructose to glucose compared to others. For example, [[apple]]s and [[pear]]s contain more than twice as much free fructose as glucose, while for [[apricot]]s the proportion is less than half as much fructose as glucose.

Apple and pear juices are of particular interest to [[pediatrics|pediatricians]] because the high concentrations of free fructose in these juices can cause [[diarrhea]] in children. The cells ([[enterocyte]]s) that line children's [[small intestine]]s have less affinity for fructose [[Small Intestine#Absorptions|absorption]] than for glucose and sucrose.<ref name="AJCN fructose absorption">{{cite journal|last=Riby|first=JE|author2=Fujisawa T |author3=Kretchmer N |title=Fructose absorption|year=1993|journal=American Journal of Clinical Nutrition|volume=58|pages=748S–753S|pmid=8213606|issue=5 Suppl|doi=10.1093/ajcn/58.5.748S|doi-access=free}}</ref> Unabsorbed fructose creates higher [[osmolarity]] in the small intestine, which draws water into the gastrointestinal tract, resulting in osmotic diarrhea. This phenomenon is discussed in greater detail in the [[#Potential health effects|Health Effects]] section.

Table 1 also shows the amount of sucrose found in common fruits and vegetables. [[Sugarcane]] and [[sugar beet]] have a high concentration of sucrose, and are used for commercial preparation of pure sucrose. Extracted cane or beet juice is clarified, removing impurities; and concentrated by removing excess water. The end product is 99.9%-pure sucrose. Sucrose-containing sugars include common white sugar and [[powdered sugar]], as well as [[brown sugar]].<ref name=Kretchmer>{{cite book|last=Kretchmer|first=N|author2=Hollenbeck CB|title=Sugars and Sweeteners|year=1991|publisher=CRC Press, Inc.}}</ref>

{|class="wikitable" style="text-align:center; margin:auto"
|+Sugar content of selected common plant foods (g/100g)<ref name="www.nal.usda.gov">Use [https://fdc.nal.usda.gov/fdc-app.html#/ link to FoodData Central (USDA)] {{Webarchive|url=https://web.archive.org/web/20191025172925/https://fdc.nal.usda.gov/fdc-app.html#/ |date=2019-10-25 }} and then search for the particular food, and click on "SR Legacy Foods".</ref><br>{{Fix|text=Some of these ratios don't agree}}
!Food Item
!Total<br />carbohydrate{{ref|2|A}}<br />including<br />"[[dietary fiber]]"
!Total<br />sugars
!Free<br />fructose
!Free<br />glucose
!Sucrose
!Fructose/<br />glucose<br />ratio
!Sucrose<br />as a % of<br />total sugars
!Free fructose<br>as a % of<br>total sugars
|-
!colspan=9|Fruits
|-
| [[Apple]] || 13.8|| 10.4|| 5.9|| 2.4|| 2.1|| 2.0?|| 19.9
|57
|-
| [[Apricot]]|| 11.1|| 9.2|| 0.9|| 2.4|| 5.9|| 0.7?|| 63.5
|10
|-
| [[Banana]]|| 22.8|| 12.2|| 4.9|| 5.0|| 2.4|| 1.0|| 20.0
|40
|-
| [[Ficus|Fig]], dried|| 63.9|| 47.9|| 22.9|| 24.8|| 0.9?|| 0.93|| 1.9
|47.8
|-
| [[Grape]]s|| 18.1|| 15.5|| 8.1|| 7.2|| 0.2|| 1.1|| 1
|52
|-
| [[Navel orange]]|| 12.5|| 8.5|| 2.25|| 2.0|| 4.3|| 1.1|| 50.4
|26
|-
| [[Peach]]|| 9.5|| 8.4|| 1.5|| 2.0|| 4.8|| 0.9?|| 56.7
|18
|-
| [[Pear]]|| 15.5|| 9.8|| 6.2|| 2.8|| 0.8|| 2.1?|| 8.0
|63
|-
| [[Pineapple]]|| 13.1|| 9.9|| 2.1|| 1.7|| 6.0|| 1.1|| 60.8
|21
|-
| [[Plum]]|| 11.4|| 9.9|| 3.1|| 5.1|| 1.6|| 0.66|| 16.2
|31
|-
!colspan=9|Vegetables
|-
| [[Beet]], Red|| 9.6|| 6.8|| 0.1|| 0.1|| 6.5||1.0|| 96.2
|1.5
|-
| [[Carrot]]|| 9.6|| 4.7|| 0.6|| 0.6|| 3.6|| 1.0|| 77
|13
|-
| [[Chili pepper|Red Pepper]], Sweet|| 6.0|| 4.2|| 2.3|| 1.9|| 0.0|| 1.2|| 0.0
|55
|-
| [[Onion]], Sweet|| 7.6|| 5.0|| 2.0|| 2.3|| 0.7|| 0.9|| 14.3
|40
|-
| [[Sweet Potato]]||20.1|| 4.2|| 0.7|| 1.0|| 2.5|| 0.9|| 60.3
|17
|-
| [[Yam (vegetable)|Yam]]|| 27.9|| 0.5|| tr|| tr|| tr|| na|| tr
|
|-
| [[Sugar Cane]]|| || 13–18|| 0.2 – 1.0|| 0.2 – 1.0|| 11–16|| 1.0|| high
|1.5-5.6
|-
| [[Sugar Beet]]|| || 17–18|| 0.1 – 0.5|| 0.1 – 0.5||16–17|| 1.0|| high
|0.59-2.8
|-
!colspan=9|Grains
|-
| [[Maize]], Sweet|| 19.0|| 6.2|| 1.9|| 3.4|| 0.9|| 0.61|| 15.0
|31
|}
: {{note|2|A}} The carbohydrate figure is calculated in FoodData Central and does not always correspond to the sum of the sugars, the starch, and the "dietary fiber".

All data with a unit of g (gram) are based on 100&nbsp;g of a food item.
The fructose/glucose ratio is calculated by dividing the sum of free fructose plus half sucrose by the sum of free glucose plus half sucrose.

Fructose is also found in the manufactured [[Sugar substitute|sweetener]], high-fructose corn syrup (HFCS), which is produced by treating [[corn syrup]] with [[enzyme]]s, converting glucose into fructose.<ref name="fda2014">{{cite web|url=https://www.fda.gov/Food/IngredientsPackagingLabeling/FoodAdditivesIngredients/ucm324856.htm|title=High Fructose Corn Syrup: Questions and Answers|publisher=US Food and Drug Administration|date=5 November 2014|access-date=18 December 2017|url-status=dead|archive-url=https://web.archive.org/web/20180125013538/https://www.fda.gov/Food/IngredientsPackagingLabeling/FoodAdditivesIngredients/ucm324856.htm|archive-date=25 January 2018}}</ref> The common designations for fructose content, HFCS-42 and HFCS-55, indicate the percentage of fructose present in HFCS.<ref name="fda2014" /> HFCS-55 is commonly used as a sweetener for [[soft drink]]s, whereas HFCS-42 is used to sweeten processed foods, [[breakfast cereals]], [[bakery]] foods, and some soft drinks.<ref name=fda2014/>

=== Carbohydrate content of commercial sweeteners (percent on dry basis) ===
{| class="wikitable sortable" style="text-align:center; margin:auto"
|-
! Sugar
! Fructose
! [[Glucose]]
! [[Sucrose]]<br />(Fructose+Glucose)
! Other<br />sugars
|-
| Granulated sugar
| 0
| 0
| 100

| 0
|-
| Caramel
| 1
| 1
| 97
| 1
|-
| HFCS-42
| 42
| 53
| 0
| 5
|-
| HFCS-55
| 55
| 41
| 0
| 4
|-
| HFCS-90
| 90
| 5
| 0
| 5
|-
| Honey
| 50
| 44
| 1
| 5
|-
| Maple syrup
| 1
| 4
| 95
| 0
|-
| Molasses
| 23
| 21
| 53
| 3
|-
| Tapioca Syrup
| 55
| 45
| 0
| 0
|-
| Corn syrup
| 0
| 98
| 0
| 2
|}
<ref name=Kretchmer /> for HFCS, and USDA for fruits and vegetables and the other refined sugars.<ref name="www.nal.usda.gov" />

Cane and beet sugars have been used as the major sweetener in food manufacturing for centuries. However, with the development of HFCS, a significant shift occurred in the type of sweetener consumption in certain countries, particularly the United States.<ref name=white>{{cite journal|pmid=19064536|year=2008|last1=White|first1=J. S|title=Straight talk about high-fructose corn syrup: What it is and what it ain't|journal=American Journal of Clinical Nutrition|volume=88|issue=6|pages=1716S–1721S|doi=10.3945/ajcn.2008.25825B|doi-access=free}}</ref> Contrary to the popular belief, however, with the increase of HFCS consumption, the total fructose intake relative to the total glucose intake has not dramatically changed. Granulated sugar is 99.9%-pure sucrose, which means that it has equal ratio of fructose to glucose. The most commonly used forms of HFCS, HFCS-42, and HFCS-55, have a roughly equal ratio of fructose to glucose, with minor differences. HFCS has simply replaced sucrose as a sweetener. Therefore, despite the changes in the sweetener consumption, the ratio of glucose to fructose intake has remained relatively constant.<ref>{{cite journal | last=Guthrie | first=FJ |author2=Morton FJ | title=Food sources of added sweeteners in the diets of Americans | year=2000 | journal=Journal of the American Dietetic Association | volume=100 | issue=1 | pages=43–51 | doi=10.1016/S0002-8223(00)00018-3| pmid=10646004 }}</ref>

[[File:U.s.sugarconsumption.2.svg|thumb|center|400px|Adjusted consumption of refined sugar per capita in the US]]

===Nutritional information===
Providing 368 kcal per 100 grams of dry powder (table), fructose has 95% the [[Calorie|caloric value]] of sucrose by weight.<ref name="usda-fructose">{{cite web|url=https://ndb.nal.usda.gov/ndb/foods/show/8681|title=Calories and nutrient composition for fructose, dry powder per 100 g|publisher=USDA National Nutrient Database, version SR-28|date=May 2016|url-status=dead|archive-url=https://web.archive.org/web/20170208033356/https://ndb.nal.usda.gov/ndb/foods/show/8681|archive-date=2017-02-08}}</ref><ref name="usda-sucrose">{{cite web|url=https://ndb.nal.usda.gov/ndb/foods/show/6319|title=Calories and nutrient composition for sucrose granules per 100 g|publisher=USDA National Nutrient Database, version SR-28|date=May 2016|url-status=dead|archive-url=https://web.archive.org/web/20170208035756/https://ndb.nal.usda.gov/ndb/foods/show/6319|archive-date=2017-02-08}}</ref> Fructose powder is 100% carbohydrates and supplies no other [[nutrient]]s in significant amount (table).

{{nutritional value | name=Fructose, dry powdered
| kcal=368
| protein=0 g
| fat=0 g
| carbs=100 g
| calcium_mg=0
| iron_mg=0.1
| phosphorus_mg=0
| sodium_mg=12
| potassium_mg=0
| source_usda = 1
| note=[https://web.archive.org/web/20170208033356/https://ndb.nal.usda.gov/ndb/foods/show/8681 Full Link to USDA Database entry]
}}

== Fructose digestion and absorption in humans ==
{{more citations needed | section|date=May 2020}}
[[File:Sucrase.svg|thumb|right|300px|Hydrolysis of sucrose to glucose and fructose by sucrase]]
[[File:Fructosetransporter.svg|thumb|right|300px|Intestinal sugar transport proteins]]
Fructose exists in foods either as a monosaccharide (free fructose) or as a unit of a disaccharide (sucrose). Free fructose is a ketonic simple sugar and one of the three dietary monosaccharides absorbed directly by the intestine. When fructose is consumed in the form of sucrose, it is digested (broken down) and then absorbed as free fructose. As sucrose comes into contact with the membrane of the small intestine, the enzyme [[sucrase]] catalyzes the cleavage of sucrose to yield one glucose unit and one fructose unit, which are then each absorbed. After absorption, it enters the [[hepatic portal vein]] and is directed toward the liver.

The mechanism of fructose absorption in the small intestine is not completely understood. Some evidence suggests [[active transport]], because fructose uptake has been shown to occur against a concentration gradient.<ref>{{cite book | last=Stipanuk | first=Marsha H | title=Biochemical, Physiological, and Molecular Aspects of Human Nutrition, 2nd Edition | publisher=W.B. Saunders, Philadelphia, PA | year=2006}}</ref> However, the majority of research supports the claim that fructose absorption occurs on the mucosal membrane via [[facilitated diffusion|facilitated transport]] involving [[GLUT5]] transport proteins.<ref name=Shi>{{cite journal |last1=Shi |first1=Ya-Nan |last2=Liu |first2=Ya-Jin |last3=Xie |first3=Zhifang |last4=Zhang |first4=Weiping J. |date=5 June 2021 |title=Fructose and metabolic diseases: too much to be good |journal=Chinese Medical Journal |volume=134 |issue=11 |pages=1276–1285 |doi=10.1097/CM9.0000000000001545 |pmid=34010200 |pmc=8183764 }}</ref> Since the concentration of fructose is higher in the lumen, fructose is able to flow down a concentration gradient into the [[enterocytes]], assisted by transport proteins. Fructose may be transported out of the enterocyte across the basolateral membrane by either [[GLUT2]] or GLUT5, although the GLUT2 transporter has a greater capacity for transporting fructose, and, therefore, the majority of fructose is transported out of the enterocyte through GLUT2.<ref name=Shi/>

=== Capacity and rate of absorption ===
The absorption capacity for fructose in monosaccharide form ranges from less than 5&nbsp;g to 50&nbsp;g (per individual serving) and adapts with changes in dietary fructose intake.<ref name=fuji /> Studies show the greatest absorption rate occurs when glucose and fructose are administered in equal quantities.<ref name=fuji>{{cite journal | last=Fujisawa | first=T |author2=Riby J |author3=Kretchmer N  | title=Intestinal absorption of fructose in the rat | year=1991 | journal=Gastroenterology | volume=101 | pages=360–367 | pmid=2065911 | issue=2| doi=10.1016/0016-5085(91)90012-a }}</ref> When fructose is ingested as part of the disaccharide sucrose, absorption capacity is much higher because fructose exists in a 1:1 ratio with glucose. It appears that the [[GLUT5]] transfer rate may be saturated at low levels, and absorption is increased through joint absorption with glucose.<ref>{{cite journal | last=Ushijima | first=K |author2=Fujisawa T |author3=Riby J |author4=Kretchmer N  | title= Absorption of fructose by isolated small intestine of rats is via a specific saturable carrier in the absence of glucose and by the disaccharidase-related transport system in the presence of glucose | year=1991 | journal= Journal of Nutrition | volume=125 | pages=2156–2164 | pmid=7643250 | issue=8| doi=10.1093/jn/125.8.2156 }}</ref> One proposed mechanism for this phenomenon is a glucose-dependent [[cotransport]] of fructose.
In addition, fructose transfer activity increases with dietary fructose intake. The presence of fructose in the lumen causes increased mRNA transcription of GLUT5, leading to increased transport proteins. High-fructose diets (>2.4 g/kg body wt) increase the transport proteins within three days of intake.<ref>{{cite journal | last=Ferraris | first=R | title= Dietary and developmental regulation of intestinal sugar transport | year=2001 | journal= Biochemical Journal| volume=360 | pages=265–276 | pmid=11716754 | doi= 10.1042/0264-6021:3600265 | issue=Pt 2 | pmc=1222226}}</ref>

=== Malabsorption ===
{{Main|Fructose malabsorption}}

Several studies have measured the intestinal absorption of fructose using the [[hydrogen breath test]].<ref name=Beyer>{{cite journal | last=Beyer | first=PL |author2=Caviar EM |author3=McCallum RW  | title=Fructose intake at current levels in the United States may cause gastrointestinal distress in normal adults | year=2005 | journal=J. Am. Diet. Assoc. | volume=105 | pages=1559–1566 | doi=10.1016/j.jada.2005.07.002 | pmid=16183355 | issue=10}}</ref><ref>{{cite journal | last= Ravich | first=WJ |author2=Bayless TM |author3=Thomas, M | title=Fructose: incomplete intestinal absorption in humans | year=1983 | journal=Gastroenterology | volume=84 | pages=26–29 | pmid= 6847852 | issue= 1| doi=10.1016/S0016-5085(83)80162-0 | doi-access=free }}</ref><ref>{{cite journal | last=Riby | first=JE |author2=Fujisawa T |author3=Kretchmer, N | title=Fructose absorption | year=1993 | journal=American Journal of Clinical Nutrition | volume=58 | pages=748S–753S | pmid=8213606 | issue=5 Suppl | doi=10.1093/ajcn/58.5.748S| doi-access=free }}</ref><ref>{{cite journal | last=Rumessen | first=JJ |author2=Gudman-Hoyer E | title= Absorption capacity of fructose in healthy adults. Comparison with sucrose and its constituent monosaccharides | year=1986 | journal=Gut | volume=27 | pages=1161–1168 | doi= 10.1136/gut.27.10.1161 | pmid= 3781328 | issue=10 | pmc=1433856}}</ref> These studies indicate that fructose is not completely absorbed in the small intestine. When fructose is not absorbed in the small intestine, it is transported into the large intestine, where it is fermented by the colonic flora. Hydrogen is produced during the [[fermentation (biochemistry)|fermentation]] process and dissolves into the blood of the [[portal vein]]. This hydrogen is transported to the lungs, where it is exchanged across the lungs and is measurable by the hydrogen breath test. The colonic flora also produces carbon dioxide, [[short-chain fatty acid]]s, organic acids, and trace gases in the presence of unabsorbed fructose.<ref>{{cite journal | last=Skoog | first=SM |author2=Bharucha AE | title= Dietary fructose and gastrointestinal symptoms: a review | year=2004 | journal=Am. J. Gastroenterol. | volume=99 | pages=2046–50 | pmid=15447771 | issue=10| doi=10.1111/j.1572-0241.2004.40266.x | s2cid=12084142 }}</ref> The presence of gases and organic acids in the large intestine causes gastrointestinal symptoms such as bloating, diarrhea, flatulence, and gastrointestinal pain.<ref name=Beyer /> Exercise immediately after consumption can exacerbate these symptoms by decreasing transit time in the small intestine, resulting in a greater amount of fructose emptied into the large intestine.<ref>{{cite journal | last1=Fujisawa, T |author2=Mulligan K |author3=Wada L |author4=Schumacher L |author5=Riby J |author6=Kretchmer N  | title=The effect of exercise on fructose absorption | year=1993 | journal=Am. J. Clin. Nutr. | volume=58 | pages=75–9 | pmid=8317393 | first1=T | issue=1|doi=10.1093/ajcn/58.1.75 | doi-access=free }}</ref>

== Fructose metabolism ==
The liver converts most fructose and galactose into glucose for distribution in the bloodstream or deposition into [[glycogen]].<ref>{{cite journal | url=https://diabetesjournals.org/care/article/25/2/353/23338/Increased-Fructose-Concentrations-in-Blood-and | doi=10.2337/diacare.25.2.353 | title=Increased Fructose Concentrations in Blood and Urine in Patients with Diabetes | date=2002 | last1=Kawasaki | first1=Takahiro | last2=Akanuma | first2=Hiroshi | last3=Yamanouchi | first3=Toshikazu | journal=Diabetes Care | volume=25 | issue=2 | pages=353–357 | pmid=11815509 | url-access=subscription }}</ref>

All three dietary monosaccharides are transported into the liver by the GLUT2 transporter.<ref>{{cite book | first=R | last=Quezada-Calvillo | title=Carbohydrate Digestion and Absorption | place=Missouri | publisher=Saunders, Elsevier | year=2006 | isbn=978-1-4160-0209-3 | pages=182–185 |author2=Robayo CC |author3=Nichols BL }}</ref> Fructose and [[galactose]] are [[phosphorylation|phosphorylated]] in the liver by [[fructokinase]] ([[Michaelis–Menten kinetics|K<sub>m</sub>]]= 0.5 mM) and [[galactokinase]] (K<sub>m</sub> = 0.8 mM), respectively. By contrast, glucose tends to pass through the liver (K<sub>m</sub> of hepatic glucokinase = 10 mM) and can be metabolised anywhere in the body. Uptake of fructose by the liver is not regulated by insulin. However, insulin is capable of increasing the abundance and functional activity of GLUT5, fructose transporter, in skeletal muscle cells.<ref>{{cite journal|last1=Hajduch|author2=Litherland GJ |author3=Turban S |author4=Brot-Laroche E |author5=Hundal HS |title=Insulin regulates the expression of the GLUT5 transporter in L6 skeletal muscle cells|date=Aug 2003|pmid=12914929|first1=E|volume=549|issue=1–3|pages=77–82|journal=FEBS Letters|doi=10.1016/S0014-5793(03)00773-7|s2cid=25952139 |doi-access=free|bibcode=2003FEBSL.549...77H }}</ref>

=== Fructolysis ===
{{Main|Fructolysis}}

The initial [[catabolism]] of fructose is sometimes referred to as [[fructolysis]], in analogy with [[glycolysis]], the catabolism of glucose. In fructolysis, the enzyme [[fructokinase]] initially produces [[fructose 1-phosphate]], which is split by [[aldolase B]] to produce the [[triose]]s [[dihydroxyacetone phosphate]] (DHAP) and [[glyceraldehyde]]. Unlike glycolysis, in fructolysis the triose [[glyceraldehyde]] lacks a [[phosphate group]]. A third enzyme, [[triokinase]], is therefore required to phosphorylate glyceraldehyde, producing [[glyceraldehyde 3-phosphate]]. The resulting trioses are identical to those obtained in glycolysis and can enter the [[gluconeogenesis|gluconeogenic]] pathway for glucose or glycogen synthesis, or be further catabolized through the lower glycolytic pathway to [[pyruvic acid|pyruvate]].

=== Metabolism of fructose to DHAP and glyceraldehyde ===
The first step in the metabolism of fructose is the phosphorylation of fructose to fructose 1-phosphate by fructokinase, thus trapping fructose for metabolism in the liver. Fructose 1-phosphate then undergoes [[hydrolysis]] by [[aldolase B]] to form DHAP and glyceraldehydes; DHAP can either be [[isomerization|isomerized]] to glyceraldehyde 3-phosphate by triosephosphate isomerase or undergo reduction to glycerol 3-phosphate by glycerol 3-phosphate dehydrogenase. The glyceraldehyde produced may also be converted to glyceraldehyde 3-phosphate by glyceraldehyde kinase or further converted to glycerol 3-phosphate by glycerol 3-phosphate dehydrogenase.  The metabolism of fructose at this point yields intermediates in the gluconeogenic pathway leading to glycogen synthesis as well as fatty acid and triglyceride synthesis.

=== Synthesis of glycogen from DHAP and glyceraldehyde 3-phosphate ===
The resultant glyceraldehyde formed by aldolase B then undergoes phosphorylation to glyceraldehyde 3-phosphate. Increased concentrations of DHAP and glyceraldehyde 3-phosphate in the liver drive the gluconeogenic pathway toward glucose and subsequent glycogen synthesis.<ref>{{cite journal | author1=MA Parniak |author2=Kalant N | title= Enhancement of glycogen concentrations in primary cultures of rat hepatocytes exposed to glucose and fructose | year=1988 | journal=Biochemical Journal | volume=251 | pages=795–802 | pmid=3415647 | issue=3 | pmc=1149073 | doi=10.1042/bj2510795}}</ref> It appears that fructose is a better substrate for glycogen synthesis than glucose and that glycogen replenishment takes precedence over triglyceride formation.<ref>{{Cite journal|last1=Jia|first1=Guanghong|last2=Aroor|first2=Annayya R.|last3=Whaley-Connell|first3=Adam T.|last4=Sowers|first4=James R.|date=June 2014|title=Fructose and Uric Acid: Is There a Role in Endothelial Function?|journal=Current Hypertension Reports|language=en|volume=16|issue=6|pages=434|doi=10.1007/s11906-014-0434-z|issn=1522-6417|pmc=4084511|pmid=24760443}}</ref> Once liver glycogen is replenished, the intermediates of fructose metabolism are primarily directed toward triglyceride synthesis.<ref>{{Cite journal|last=Medina Villaamil|date=2011-02-01|title=Fructose transporter Glut5 expression in clear renal cell carcinoma|journal=Oncology Reports|language=en|volume=25|issue=2|pages=315–23|doi=10.3892/or.2010.1096|pmid=21165569|issn=1021-335X|doi-access=free|hdl=2183/20620|hdl-access=free}}</ref>

[[File:Fructose-glycogen.svg|thumb|center|400px|Metabolic conversion of fructose to glycogen in the liver]]

=== Synthesis of triglyceride from DHAP and glyceraldehyde 3-phosphate ===
Carbons from dietary fructose are found in both the [[free fatty acid]] and glycerol [[Moiety (chemistry)|moieties]] of plasma triglycerides. High fructose consumption can lead to excess [[pyruvate]] production, causing a buildup of [[Krebs cycle]] intermediates.<ref name=McGrane>{{cite book | first=MM | last=McGrane | title=Carbohydrate metabolism: Synthesis and oxidation | place=Missouri | publisher=Saunders, Elsevier | year=2006 | isbn=978-1-4160-0209-3 | pages=258–277}}</ref> Accumulated citrate can be transported from the [[mitochondrion|mitochondria]] into the [[cytosol]] of [[hepatocytes]], converted to [[acetyl CoA]] by citrate lyase and directed toward fatty acid synthesis.<ref name=McGrane /><ref name=Sul>{{cite book | first=HS | last=Sul | title=Metabolism of Fatty Acids, Acylglycerols, and Sphingolipids | place=Missouri | publisher=Saunders, Elsevier | year=2006 | isbn=978-1-4160-0209-3 | pages=450–467}}</ref> In addition, DHAP can be converted to glycerol 3-phosphate, providing the glycerol backbone for the triglyceride molecule.<ref name=Sul /> Triglycerides are incorporated into [[very-low-density lipoprotein]]s (VLDL), which are released from the liver destined toward peripheral tissues for storage in both fat and muscle cells.

[[File:Fructose-triglyceride.svg|thumb|center|400px|Metabolic conversion of fructose to triglyceride in the liver]]

== Potential health effects ==
In 2022, the European Food Safety Authority stated that there is research evidence that fructose and other added free sugars may be associated with increased risk of several chronic diseases:<ref name=efsa11/><ref name=efsa2-22/> the risk is moderate for obesity and [[dyslipidemia]] (more than 50%), and low for [[non-alcoholic fatty liver disease]], [[type 2 diabetes]] (from 15% to 50%) and [[hypertension]]. EFSA further stated that clinical research did "not support a positive relationship between the intake of dietary sugars, in isocaloric exchange with other macronutrients, and any of the chronic metabolic diseases or pregnancy-related endpoints assessed" but advised "the intake of added and free sugars should be as low as possible in the context of a nutritionally adequate diet."<ref name="efsa2-22">{{Cite journal |author=EFSA Panel on Nutrition, Novel Foods and Food Allergens |date=28 February 2022 |title=Tolerable upper intake level for dietary sugars |url=https://doi.org/10.2903/j.efsa.2022.7074 |journal=EFSA Journal |volume=20 |issue=2 |pages=337 |doi=10.2903/j.efsa.2022.7074 |pmid=35251356 |pmc=8884083 |hdl=1854/LU-01GWHCPEH24E9RRDYANKYH53MJ |s2cid=247184182 |issn=1831-4732 |via=ESFA |access-date=3 October 2022 |archive-date=26 October 2023 |archive-url=https://web.archive.org/web/20231026085708/https://efsa.onlinelibrary.wiley.com/doi/full/10.2903/j.efsa.2022.7074 |url-status=live }}</ref>

===Obesity===
Excessive consumption of sugars, including fructose, contributes to [[insulin resistance]], [[obesity]], elevated [[low-density lipoprotein|LDL cholesterol]] and [[triglyceride]]s, leading to [[metabolic syndrome]]. The [[European Food Safety Authority]] (EFSA) stated in 2011 that fructose may be preferable over sucrose and glucose in sugar-sweetened foods and beverages because of its lower effect on [[postprandial]] [[blood sugar]] levels,<ref name=efsa11/> while also noting the potential downside that "high intakes of fructose may lead to metabolic complications such as [[dyslipidaemia]], insulin resistance, and increased visceral adiposity".<ref name="efsa11">{{cite journal | title=Scientific Opinion on the substantiation of health claims related to fructose and reduction of post-prandial glycaemic responses (ID 558) pursuant to Article 13(1) of Regulation (EC) No 1924/2006 | publisher= EFSA Panel on Dietetic Products, Nutrition and Allergies | journal=EFSA Journal | year=2011 | volume=9 | issue=6 | pages=2223 | doi= 10.2903/j.efsa.2011.2223 | doi-access=free|quote=The Panel notes that these values support a significant decrease in post-prandial blood glucose responses when fructose replaces either sucrose or glucose.}}</ref><ref name=efsa2-22/> The UK's Scientific Advisory Committee on Nutrition in 2015 disputed the claims of fructose causing metabolic disorders, stating that "there is insufficient evidence to demonstrate that fructose intake, at levels consumed in the normal UK diet, leads to adverse health outcomes independent of any effects related to its presence as a component of total and free sugars."<ref>{{cite web| url= https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/445503/SACN_Carbohydrates_and_Health.pdf|title=Carbohydrates and Health|publisher=UK Scientific Advisory Committee on Nutrition, Public Health England, TSO| place= Williams Lea, Norwich, UK|date=2015|access-date=1 April 2016|url-status=live|archive-url= https://web.archive.org/web/20160319190958/https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/445503/SACN_Carbohydrates_and_Health.pdf|archive-date=19 March 2016}}</ref>

=== Cardiometabolic diseases ===
When fructose is consumed in excess as a sweetening agent in foods or beverages, it may be associated with increased risk of obesity, diabetes, and cardiovascular disorders that are part of [[metabolic syndrome]].<ref name=efsa2-22/> 

=== Compared with sucrose ===
Fructose was found to increase [[triglyceride]]s in type-2 but not type-1 diabetes, and moderate use of it has previously been considered acceptable as a sweetener for diabetics,<ref name="Rizkalla">{{cite journal | last=Rizkalla | first=Salwa W | title=Health implications of fructose consumption: A review of recent data | journal=Nutrition & Metabolism| volume=7 | issue=1 | year=2010 | issn=1743-7075 | doi=10.1186/1743-7075-7-82 | page=82|pmid=21050460|pmc=2991323 | doi-access=free }}</ref> possibly because it does not trigger the production of insulin by pancreatic [[Beta cell|β cells]].<ref name="Thorens">{{cite journal | last1=Thorens | first1=Bernard | last2=Mueckler | first2=Mike | title=Glucose transporters in the 21st Century (Review)| journal=American Journal of Physiology. Endocrinology and Metabolism | volume=298 | issue=2 | year=2010 | issn=0193-1849 | doi=10.1152/ajpendo.00712.2009 | pages=E141–E145|pmid=20009031|pmc=2822486}}</ref> For a 50 gram reference amount, fructose has a [[glycemic index]] of 23, compared with 100 for glucose and 60 for sucrose.<ref name="gitr">{{cite web|title=Glycemic index|url=http://www.glycemicindex.com/foodSearch.php|publisher=Glycemic Index Testing and Research, University of Sydney (Australia) Glycemic Index Research Service (SUGiRS)|access-date=23 February 2018|date=2 May 2017|archive-date=16 January 2021|archive-url=https://web.archive.org/web/20210116021928/https://glycemicindex.com/foodSearch.php|url-status=live}}</ref> Fructose is also 73% [[#Sweetness of fructose|sweeter]] than sucrose at room temperature, allowing diabetics to use less of it per serving. Fructose consumed before a meal may reduce the glycemic response of the meal.<ref name=":0">{{cite journal | author1 = Patricia M. Heacock | author2 = Steven R. Hertzler | author3 = Bryan W. Wolf | year = 2002 | title = Fructose Prefeeding Reduces the Glycemic Response to a High-Glycemic Index, Starchy Food in Humans | journal = Journal of Nutrition | volume = 132 | issue = 9 | pages = 2601–2604 | pmid = 12221216 | doi = 10.1093/jn/132.9.2601 | doi-access = free }}</ref> Fructose-sweetened food and beverage products cause less of a rise in blood glucose levels than do those manufactured with either sucrose or glucose.<ref name=efsa11/>

== See also ==
* [[Hereditary fructose intolerance]]
* [[Inverted sugar syrup]]

== References ==
{{reflist}}

==External links==
*{{Commons category-inline}}

{{Fructose and galactose metabolic intermediates}}
{{Inborn errors of carbohydrate metabolism}}
{{Fructose and galactose metabolism enzymes}}
{{Carbohydrates}}
{{Sugar}}
{{Authority control}}

[[Category:Ketohexoses]]
[[Category:Nutrition]]
[[Category:Types of sugar]]
[[Category:Furanoses]]
[[Category:Pyranoses]]