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Fructose, or fruit sugar, is a
ketonic
ketonic
simple sugar Monosaccharides (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is app ...
found in many plants, where it is often bonded to
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
to form the
disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of ...
sucrose Sucrose is a type of sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosacchari ...

sucrose
. It is one of the three dietary monosaccharides, along with glucose and
galactose Galactose (, '' galacto-'' + ''-ose The suffix In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. ...
, that are absorbed directly into blood during
digestion Digestion is the breakdown of large insoluble food Food is any substance consumed to provide nutritional Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to liv ...
. Fructose was discovered by French chemist
Augustin-Pierre DubrunfautAugustin-Pierre Dubrunfaut (; 1 September 1797, Lille Lille ( , ; nl, Rijsel ; pcd, Lile; vls, Rysel) is a city at the northern part of France France (), officially the French Republic (french: link=no, République française), is a cou ...
in 1847. The name "fructose" was coined in 1857 by the English chemist
William Allen Miller William Allen Miller FRS (17 December 1817 – 30 September 1870) was a British scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, area of interest. In c ...
. Pure, dry fructose is a sweet, white, odorless, crystalline solid, and is the most water-soluble of all the sugars. Fructose is found in
honey Honey is a sweet, viscous food substance made by and some other . Bees produce honey from the y secretions of plants (floral ) or from secretions of other insects (such as ), by , activity, and water evaporation. Honey bees store honey in w ...

honey
, tree and vine fruits, flowers,
berries A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone or pit, although many pips or seeds may be present. Common examples are strawberries, raspbe ...

berries
, and most
root vegetables Root vegetables are underground plant parts eaten by humans as food. Although botany Botany, also called , plant biology or phytology, is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic en ...
. Commercially, fructose is derived from
sugar cane Sugarcane or sugar cane is a species of (often hybrid) tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall w ...

sugar cane
,
sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet (''Beta vulgaris''). Together wit ...
s, and
maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It can also be ...

maize
.
High-fructose corn syrup High-fructose corn syrup (HFCS), also known as glucose-fructose, isoglucose and glucose-fructose syrup, is a sweetener made from corn starch. As in the production of conventional corn syrup, the starch is broken down into glucose by enzymes. ...
is a
mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, ...

mixture
of glucose and fructose as monosaccharides. Sucrose is a
compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive structu ...
with one molecule of glucose
covalently A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they s ...
linked to one molecule of fructose. All forms of fructose, including fruits and juices, are commonly added to foods and drinks for
palatabilityPalatability is the Reward system, hedonic reward (i.e., pleasure) provided by foods or fluids that are agreeable to the "palate", which often varies relative to the homeostatic satisfaction of nutritional, Fluid balance, water, or Food energy, energ ...
and
taste The gustatory system or sense of taste is the sensory system The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory re ...

taste
enhancement, and for browning of some foods, such as baked goods. About 240,000
tonne The tonne ( or ; symbol: t) is a metric unit of mass equal to 1,000 kilogram The kilogram (also kilogramme) is the base unit of mass in the International System of Units (SI), the current metric system, having the unit symbol kg. I ...
s of crystalline fructose are produced annually. Excessive consumption of fructose (especially from sugar-sweetened beverages) may contribute to
insulin resistance Insulin resistance (IR) is a pathological condition in which cell (biology), cells fail to respond normally to the hormone insulin. Insulin is a hormone that allows glucose to enter cells which also reduces blood glucose (blood sugar). Insulin is ...
,
obesity Obesity is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any immediate external injury. Diseases are often ...

obesity
, elevated
LDL cholesterol Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein which transport all fat molecules around the body in the extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall ...
and
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an derived from and three (from ' and '). Triglycerides are the main constituents of in humans and other vertebrates, as well as . They are also present in the blood to enab ...

triglyceride
s, leading to
metabolic syndrome Metabolic syndrome is a clustering of at least three of the following five medical conditions: abdominal obesity Abdominal obesity, also known as central obesity and truncal obesity, is a condition when excessive abdominal fat around the stomach ...
. The
European Food Safety Authority The European Food Safety Authority (EFSA) is the agency of the European Union The European Union (EU) is a political and economic union of Member state of the European Union, member states that are located primarily in Europe. Its member ...
stated that fructose may be preferable over sucrose and glucose in sugar-sweetened foods and beverages because of its lower effect on
postprandial Prandial relates to a meal. Postprandial (from post prandium) means after eating a meal, while preprandial is before a meal. Usages of postprandial The term ''postprandial'' is used in many contexts. Gastronomic or social Refers to activities ...
blood sugar The blood sugar level, blood sugar concentration, or blood glucose level is the concentration of glucose present in the blood of humans and other animals. Glucose is a simple sugar, and approximately 4 g of glucose are present in the blood of a 70 ...
levels, while also noting the potential downside that "high intakes of fructose may lead to metabolic complications such as
dyslipidaemia Dyslipidemia is an abnormal amount of lipids (e.g. triglycerides, cholesterol and/or fat phospholipids) in the blood. In developed countries, most dyslipidemias are hyperlipidemias; that is, an elevation of lipids in the blood. This is often due t ...
, insulin resistance, and increased visceral adiposity". 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."


Etymology

The word "fructose" was coined in 1857 from the Latin for ''fructus'' (fruit) and the generic chemical suffix for sugars, ''
-ose The suffix In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. The traditional areas of linguistic analys ...
''. It is also called fruit sugar and levulose.


Chemical properties

Fructose is a 6-carbon polyhydroxyketone. Crystalline fructose adopts a cyclic six-membered structure, called β--fructopyranose, owing to the stability of its
hemiketal of a hemiacetal Image:Hemiketal-2D-skeletal.png, 150px, Hemiketal A hemiacetal or a hemiketal is a compound that results from the addition of an alcohol File:Alcohol general.svg, upright=0.8, The bond angle between a hydroxyl group (-OH) and ...

hemiketal
and internal hydrogen-bonding. In solution, fructose exists as an
equilibrium List of types of equilibrium, the condition of a system in which all competing influences are balanced, in a wide variety of contexts. Equilibrium may also refer to: Film and television * Equilibrium (film), ''Equilibrium'' (film), a 2002 scien ...
mixture of the
tautomers Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. This reaction commonly results in the relocation of a hydrogen atom. Tautomerism is for example relevant to the behavior of amino acids ...

tautomers
β--fructo
pyranosePyranose is a collective term for saccharides that have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom. There may be other carbons external to the ring. The name derives from its similarity ...
, β--fructo
furanose A furanose is a collective term for carbohydrates is a disaccharide found in animal milk. It consists of a molecule of galactose, D-galactose and a molecule of glucose, D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a bio ...
, α--fructofuranose, α--fructopyranose and ''keto''--fructose (the non-cyclic form). The distribution of -fructose tautomers in solution is related to several variables, such as solvent and temperature. -Fructopyranose and -fructofuranose distributions in water have been identified multiple times as roughly 70% fructopyranose and 22% fructofuranose.


Reactions


Fructose and fermentation

Fructose may be anaerobically
fermented Fermentation is a metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling ...

fermented
by
yeast Yeasts are eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classifie ...

yeast
or
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
. Yeast enzymes convert sugar (sucrose, glucose, or fructose, but not
lactose Lactose, a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-g ...

lactose
) to
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
and
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
. Some of the carbon dioxide produced during fermentation will remain dissolved in water, where it will reach equilibrium with
carbonic acid In chemistry, carbonic acid is a dibasic acid with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical ...

carbonic acid
. The dissolved carbon dioxide and carbonic acid produce the carbonation in some fermented beverages, such as
champagne Champagne (, ) is a sparkling wine Sparkling wine is a wine Wine is an alcoholic drink typically made from fermented grape juice. Yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus ...

champagne
.


Fructose and Maillard reaction

Fructose undergoes the
Maillard reaction The Maillard reaction ( ; ) is a chemical reaction between Amino acid, amino acids and Reducing sugar, reducing sugars that gives browned food its distinctive flavor. Searing, Seared steaks, fried dumplings, cookies and other kinds of biscuits, b ...
, non-enzymatic browning, with
amino acids Amino acids are organic compounds that contain amino (–NH2) and Carboxylic acid, carboxyl (–COOH) functional groups, along with a Substituent, side chain (R group) specific to each amino acid. The key Chemical element, elements of an amino ...

amino acids
. 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
palatabilityPalatability is the Reward system, hedonic reward (i.e., pleasure) provided by foods or fluids that are agreeable to the "palate", which often varies relative to the homeostatic satisfaction of nutritional, Fluid balance, water, or Food energy, energ ...
, as well as other nutritional effects, such as excessive browning, volume and tenderness reduction during cake preparation, and formation of
mutagenic In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual cont ...
compounds.


Dehydration

Fructose readily dehydrates to give
hydroxymethylfurfural Hydroxymethylfurfural (HMF), also 5-(hydroxymethyl)furfural, is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, ...

hydroxymethylfurfural
("HMF", ), which can be processed into liquid (). This process, in the future, may become part of a low-cost, carbon-neutral system to produce replacements for petrol and diesel from plants.


Physical and functional properties


Sweetness of fructose

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 carbohydrates. The relative sweetness of fructose has been reported in the range of 1.2–1.8 times that of sucrose. 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. Therefore, the relative sweetness decreases with increasing temperature. However it has been observed that the absolute sweetness of fructose is identical at 5 °C as 50 °C and thus the relative sweetness to sucrose is not due to
anomeric An anomer is a type of geometric variation found at certain atoms in carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage. A carbohy ...
distribution but a decrease in the absolute sweetness of sucrose at lower temperatures. 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. 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.


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. Sugar mixes containing fructose, such as candies, are softer than those containing other sugars because of the greater solubility of fructose.


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. Fructose is an excellent humectant and retains moisture for a long period of time even at low
relative humidity Humidity is the concentration of water vapour (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapo ...

relative humidity
(RH). Therefore, fructose can contribute a more palatable texture, and longer shelf life to the food products in which it is used.


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.


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 gelatinizing of starch, causing a greater final viscosity. Although some artificial sweeteners are not suitable for home-baking, many traditional recipes use fructose.


Food sources

Natural sources of fructose include fruits, vegetables (including sugar cane), and honey. Fructose is often further concentrated from these sources. The highest dietary sources of fructose, besides pure crystalline fructose, are foods containing
table sugar White sugar, also called table sugar, granulated sugar or regular sugar, is a commonly used type of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated s ...
(sucrose),
high-fructose corn syrup High-fructose corn syrup (HFCS), also known as glucose-fructose, isoglucose and glucose-fructose syrup, is a sweetener made from corn starch. As in the production of conventional corn syrup, the starch is broken down into glucose by enzymes. ...
,
agave nectar Agave syrup, aka maguey syrup, and commonly though inaccurately known as agave nectar, is a Sugar substitute, sweetener commercially produced from several species of agave, including ''Agave tequilana'' (blue agave) and ''Agave salmiana''. Blue-a ...
,
honey Honey is a sweet, viscous food substance made by and some other . Bees produce honey from the y secretions of plants (floral ) or from secretions of other insects (such as ), by , activity, and water evaporation. Honey bees store honey in w ...

honey
,
molasses Molasses () or black treacle Treacle () is any uncrystallised syrup In cooking, a syrup or sirup (from ar, شراب; ''sharāb'', beverage, wine and la, sirupus) is a condiment that is a thick, viscous The viscosity of a fluid ...

molasses
,
maple syrup Maple syrup is a syrup usually made from the xylem sap of sugar maple, red maple, or black maple trees, although it can also be made from other maple species. In cold climates, these trees store starch in their trunks and roots before winter; t ...

maple syrup
, fruit and fruit
juice Juice is a drink A drink (or beverage) is a liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external ...

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 Monosaccharides (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is ap ...
or bound to glucose as
sucrose Sucrose is a type of sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosacchari ...

sucrose
, a
disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of ...
. Fructose, glucose, and sucrose may all be present in a 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 An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wher ...

apple
s and
pear Pears are fruits produced and consumed around the world, growing on a tree and harvested in the Northern Hemisphere in late summer into October. The pear tree and shrub are a species In biology, a species is the basic unit of biological ...

pear
s contain more than twice as much free fructose as glucose, while for
apricot An apricot (, ) is a fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The ...

apricot
s the proportion is less than half as much fructose as glucose. Apple and pear juices are of particular interest to
pediatricians Paediatrics ( also spelled pediatrics or pædiatrics) is the branch of medicine Medicine is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxono ...

pediatricians
because the high concentrations of free fructose in these juices can cause
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery defecation, bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration of ...
in children. The cells (
enterocyte Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biolo ...
s) that line children's
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

small intestine
s have less affinity for fructose
absorption Absorption may refer to: Chemistry and biology *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which substances enter the body through the skin *Absorption (pharmacolo ...
than for glucose and sucrose. Unabsorbed fructose creates higher
osmolarityOsmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L (pr ...
in the small intestine, which draws water into the gastrointestinal tract, resulting in osmotic diarrhea. This phenomenon is discussed in greater detail in the
Health Effects Health effects (or health impacts) are changes in health Health is a state of physical, mental and social well-being Well-being, also known as ''wellness'', ''prudential value'' or ''quality of life'', refers to what is intrinsically valuab ...
section. Table 1 also shows the amount of sucrose found in common fruits and vegetables.
Sugarcane Sugarcane or sugar cane is a species of (often hybrid) tall, perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, ...

Sugarcane
and
sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet (''Beta vulgaris''). Together wit ...
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 table and
powdered sugar Powdered sugar, also called confectioners' sugar, 10X sugar or icing sugar, is a finely ground sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide found in animal milk. It consists of a molecule o ...
, as well as
brown sugar Brown sugar is a sucrose Sucrose is a type of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular sugar, refers to sucrose, a disacc ...
. : The carbohydrate figure is calculated in the USDA database 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 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
sweetener A sugar substitute is a food additive that provides a sweetness, sweet taste like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie (non-nutritive) or low-calorie sweetener. Artif ...
,
high-fructose corn syrup High-fructose corn syrup (HFCS), also known as glucose-fructose, isoglucose and glucose-fructose syrup, is a sweetener made from corn starch. As in the production of conventional corn syrup, the starch is broken down into glucose by enzymes. ...
(HFCS), which is produced by treating
corn syrup Corn syrup is a food syrup which is made from the starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose Glucose is a simple sugar with the Chemical formula#Molecular formula, molecular formula . Glucose is the m ...

corn syrup
with
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates in ...

enzyme
s, converting glucose into fructose. The common designations for fructose content, HFCS-42 and HFCS-55, indicate the percentage of fructose present in HFCS. HFCS-55 is commonly used as a sweetener for
soft drink A soft drink (see #Terminology, § Terminology for other names) is a drink that usually contains water (often Carbonated water, carbonated), a Sweetness, sweetener, and a natural and/or Artificial Flavoring, artificial flavoring. The sweetene ...

soft drink
s, whereas HFCS-42 is used to sweeten processed foods,
breakfast cereals Cereal, often called breakfast cereal (and further categorized as cold cereal or warm cereal), is a traditional breakfast food made from Processed food, processed cereal, cereal grains. It is traditionally eaten as part of a Balanced diet, balanced ...
,
bakery A bakery is an Business, establishment that produces and sells flour-based food Baking, baked in an oven such as bread, cookies, cakes, Pastry, pastries, and pies. Some retail bakeries are also categorized as Coffeehouse, cafés, serving coffee and ...

bakery
foods, and some soft drinks.


Carbohydrate content of commercial sweeteners (percent on dry basis)

for HFCS, and USDA for fruits and vegetables and the other refined sugars. 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. 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.


Nutritional information

Providing 368 kcal per 100 grams of dry powder (table), fructose has 95% the
caloric value The calorie is a unit of energy defined as the amount of heat needed to raise the temperature of a quantity of water by one degree. For historical reasons, two main definitions of calorie are in wide use. The small calorie or gram calorie (usual ...
of sucrose by weight. Fructose powder is 100%
carbohydrates is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galacto ...
and supplies no other
nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and t ...
s in significant amount (table).


Fructose digestion and absorption in humans

Fructose exists in foods either as a monosaccharide (free fructose) or as a unit of a disaccharide (sucrose). Free fructose is 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 The portal vein or hepatic portal vein (HPV) is a blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tis ...
and is directed toward the liver. The mechanism of fructose absorption in the small intestine is not completely understood. Some evidence suggests
active transport In cellular biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...

active transport
, because fructose uptake has been shown to occur against a concentration gradient. However, the majority of research supports the claim that fructose absorption occurs on the mucosal membrane via facilitated transport involving GLUT5 transport proteins. Since the concentration of fructose is higher in the lumen, fructose is able to flow down a concentration gradient into the
enterocytes Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biolo ...
, assisted by transport proteins. Fructose may be transported out of the enterocyte across the basolateral membrane by either
GLUT2 Glucose transporter 2 (GLUT2) also known as solute carrier family 2 (facilitated glucose transporter), member 2 (SLC2A2) is a transmembrane Image:Polytopic membrane protein.png, 400px, Schematic representation of transmembrane proteins: 1) a single ...
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.


Capacity and rate of absorption

The absorption capacity for fructose in monosaccharide form ranges from less than 5 g to 50 g (per individual serving) and adapts with changes in dietary fructose intake. Studies show the greatest absorption rate occurs when glucose and fructose are administered in equal quantities. When fructose is ingested as part of the disaccharide
sucrose Sucrose is a type of sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosacchari ...

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. One proposed mechanism for this phenomenon is a glucose-dependent
cotransport In Cellular Biology, cellular biology, active transport is the movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires c ...
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 transport proteins within three days of intake.


Malabsorption

Several studies have measured the intestinal absorption of fructose using the
hydrogen breath test A hydrogen breath test (or HBT) is used as a diagnostic tool for small intestine bacterial overgrowth and carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by bet ...
. 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 Fermentation is a metabolism, metabolic process that produces chemical changes in organic Substrate (chemistry), substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in ...
process and dissolves into the blood of the
portal vein The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Approximat ...
. 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 acidShort-chain fatty acids (SCFAs) are fatty acids with fewer than six carbon atoms. Derived from intestine, intestinal microbe, microbial fermentation of indigestible foods, SCFAs are the main energy source of Gastrointestinal_tract#Mucosa, colonocytes ...
s, organic acids, and trace gases in the presence of unabsorbed fructose. The presence of gases and organic acids in the large intestine causes gastrointestinal symptoms such as bloating, diarrhea, flatulence, and gastrointestinal pain. 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.


Fructose metabolism

All three dietary monosaccharides are transported into the liver by the GLUT2 transporter. Fructose and
galactose Galactose (, '' galacto-'' + ''-ose The suffix In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. ...
are
phosphorylated In chemistry, phosphorylation of a molecule is the attachment of a phosphoryl group. This process and its inverse, dephosphorylation, are critical for many cellular processes in biology. Protein phosphorylation is especially important for their fu ...

phosphorylated
in the liver by
fructokinase Fructokinase (/fruc•to•ki•nase/ ki´nas, also known as D-fructokinase or D-fructose (D-mannose) kinase,
( Km= 0.5 mM) and galactokinase (Km = 0.8 mM), respectively. By contrast, glucose tends to pass through the liver (Km 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 in skeletal muscle cells.


Fructolysis

The initial
catabolism Catabolism () is the set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell ...

catabolism
of fructose is sometimes referred to as fructolysis, in analogy with
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
, the catabolism of
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
. In fructolysis, the enzyme
fructokinase Fructokinase (/fruc•to•ki•nase/ ki´nas, also known as D-fructokinase or D-fructose (D-mannose) kinase,
initially produces
fructose 1-phosphate Fructose-1-phosphate is a derivative of fructose. It is generated mainly by hepatic fructokinase but is also generated in smaller amounts in the small intestinal mucosa and proximal epithelium of the renal tubule. It is an important intermediate of ...
, which is split by
aldolase B Aldolase B also known as fructose-bisphosphate aldolase B or liver-type aldolase is one of three isoenzymes (A, B, and C) of the class I Fructose-bisphosphate aldolase, fructose 1,6-bisphosphate aldolase enzyme (EC 4.1.2.13), and plays a key role in ...
to produce the
triose A triose is a monosaccharide Monosaccharides (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southe ...
s
dihydroxyacetone phosphate Dihydroxyacetone phosphate (DHAP, also glycerone phosphate in older texts) is the anion with the formula HOCH2C(O)CH2OPO32-. This anion is involved in many metabolic pathways, including the Calvin cycle in plants and glycolysis.Nelson, D. L.; Cox ...
(DHAP) and
glyceraldehyde Glyceraldehyde (glyceral) is a triose is an aldotriose because the carbonyl group is at the end of the chain Image:Dihydroxyacetone.png">150px, Dihydroxyacetone is a ketone, ketotriose because the carbonyl group is the center of the chain. A tr ...

glyceraldehyde
. Unlike
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
, in fructolysis the triose
glyceraldehyde Glyceraldehyde (glyceral) is a triose is an aldotriose because the carbonyl group is at the end of the chain Image:Dihydroxyacetone.png">150px, Dihydroxyacetone is a ketone, ketotriose because the carbonyl group is the center of the chain. A tr ...

glyceraldehyde
lacks a
phosphate group In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms ...

phosphate group
. A third enzyme, triokinase, is therefore required to phosphorylate glyceraldehyde, producing
glyceraldehyde 3-phosphate Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL, is the metabolite In biochemistry Biochemistry or biological chemistry, is the study of chemical ...

glyceraldehyde 3-phosphate
. The resulting trioses are identical to those obtained in glycolysis and can enter the pathway for glucose or glycogen synthesis, or be further catabolized through the lower glycolytic pathway to
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

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 Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord fo ...

hydrolysis
by
aldolase B Aldolase B also known as fructose-bisphosphate aldolase B or liver-type aldolase is one of three isoenzymes (A, B, and C) of the class I Fructose-bisphosphate aldolase, fructose 1,6-bisphosphate aldolase enzyme (EC 4.1.2.13), and plays a key role in ...
to form DHAP and glyceraldehydes; DHAP can either be
isomerized In chemistry, isomers are molecules or polyatomic ions with identical molecular formulas — that is, same number of atoms of each element (chemistry), element — but distinct arrangements of atoms in space. Isomerism is existence or possibility ...
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. It appears that fructose is a better substrate for glycogen synthesis than glucose and that glycogen replenishment takes precedence over triglyceride formation. Once liver glycogen is replenished, the intermediates of fructose metabolism are primarily directed toward triglyceride synthesis.


Synthesis of triglyceride from DHAP and glyceraldehyde 3-phosphate

Carbons from dietary fructose are found in both the
free fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical co ...
and glycerol moieties of plasma triglycerides. High fructose consumption can lead to excess
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

pyruvate
production, causing a buildup of
Krebs cycle The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle – is a series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transfor ...
intermediates. Accumulated citrate can be transported from the
mitochondria A mitochondrion (; ) is a double-membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, i ...

mitochondria
into the
cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a s ...
of
hepatocytes A hepatocyte is a cell of the main parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, tho ...
, converted to
acetyl CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life i ...

acetyl CoA
by citrate lyase and directed toward fatty acid synthesis. In addition, DHAP can be converted to glycerol 3-phosphate, providing the glycerol backbone for the triglyceride molecule. Triglycerides are incorporated into
very-low-density lipoprotein Very-low-density lipoprotein (VLDL), density relative to extracellular water, is a type of lipoprotein made by the liver The liver is an organ only found in vertebrates which detoxifies various metabolites, synthesizes proteins and produces ...
s (VLDL), which are released from the liver destined toward peripheral tissues for storage in both fat and muscle cells.


Potential health effects


Weight gain

In a
meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple Randomized controlled trial, scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each i ...
of
clinical trial Clinical trials are experiments or observations done in . Such prospective biomedical or behavioral research studies on are designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as no ...

clinical trial
s with controlled feeding — where test subjects were fed a fixed amount of energy rather than being allowed to choose the amount they ate — fructose was not an independent factor for weight gain; however, fructose consumption was associated with weight gain when the fructose provided excess calories.


Cardiometabolic diseases

An expert panel of the
European Food Safety Authority The European Food Safety Authority (EFSA) is the agency of the European Union The European Union (EU) is a political and economic union of Member state of the European Union, member states that are located primarily in Europe. Its member ...
concluded that fructose is preferred in food and beverage manufacturing to replace sucrose and glucose due to the lower effect of fructose on blood glucose levels following a meal. However, when consumed in excess as a sweetening agent in foods and beverages, fructose has been associated with increased risk of obesity, diabetes, and cardiovascular disorders that are part of
metabolic syndrome Metabolic syndrome is a clustering of at least three of the following five medical conditions: abdominal obesity Abdominal obesity, also known as central obesity and truncal obesity, is a condition when excessive abdominal fat around the stomach ...
.
Clinical research Clinical research is a branch of healthcare science The following outline is provided as an overview of and topical guide to health sciences: Health sciences – are those sciences which focus on health Health is a state of physical, ...
has provided no or only limited direct evidence that fructose itself is associated with elevated
LDL cholesterol Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein which transport all fat molecules around the body in the extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall ...
and
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an derived from and three (from ' and '). Triglycerides are the main constituents of in humans and other vertebrates, as well as . They are also present in the blood to enab ...

triglyceride
s leading to metabolic syndrome, but rather indicates that excessive consumption of sugar-sweetened foods and beverages, and the concurrent increase in calorie intake, underlies metabolic syndrome. Similarly, increased consumption of sweetened foods and beverages raises risk of cardiovascular disease, including
hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not ...

hypertension
, but there is no direct
cause and effect Causality (also referred to as causation, or cause and effect) is influence by which one event Event may refer to: Gatherings of people * Ceremony A ceremony (, ) is a unified ritual A ritual is a sequence of activities involving gestur ...
relationship in humans showing that fructose is the causative factor.


Compared with sucrose

Moderate use of fructose may be recommended as a sweetener for diabetics, possibly because it does not trigger the production of insulin by pancreatic
β cells Beta cells (β cells) are a type of cell (biology), cell found in pancreatic islets that synthesize and secrete insulin and amylin. Beta cells make up 50–70% of the cells in human islets. In patients with Type 1 diabetes, beta-cell mass and func ...
. For a 50 gram reference amount, fructose has a
glycemic index The glycemic index (GI; ) is a number from 0 to 100 assigned to a food, with pure glucose arbitrarily given the value of 100, which represents the relative rise in the blood glucose level two hours after consuming that food. The GI of a specific fo ...
of 23, compared with 100 for glucose and 60 for sucrose. Fructose is also 73% 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. Fructose-sweetened food and beverage products cause less of a rise in blood glucose levels than do those manufactured with either sucrose or glucose.


See also

*
Hereditary fructose intolerance Hereditary fructose intolerance is an inborn error of metabolism, inborn error of fructose metabolism caused by a deficiency of the enzyme aldolase B. Individuals affected with HFI are asymptomatic until they ingest fructose, sucrose, or sorbitol. I ...
*
Inverted sugar syrup Inverted sugar syrup, also called invert syrup and invert sugar, is an edible mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical ele ...


References


External links

* {{Authority control Ketohexoses Nutrition Sugar substitutes