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Xylitol is a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the formula , or HO(CH2)(CHOH)3(CH2)OH; specifically, one particular stereoisomer with that structural formula. It is a colorless or white
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
line solid. It is classified as a
polyalcohol Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, containing one hydroxyl group attached to each carbon atom. They are white, water-soluble solids that c ...
and a
sugar alcohol Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, containing one hydroxyl group attached to each carbon atom. They are white, water-soluble solids that c ...
, specifically an
alditol In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, thr ...
. Of the common sugar alcohols, only
sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alco ...
is more soluble in water. The name derives from , ''xyl n' 'wood', with the suffix ''-itol'' used to denote it being a sugar alcohol. Xylitol is used as a
food additive Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives, such as vinegar ( pickling), salt ( salting), smoke ( smoking) and sugar ( crystallization), have been used f ...
and
sugar substitute A sugar substitute or artificial sweetener, is a food additive that provides a sweetness like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie () or low-calorie sweetener. Arti ...
. Its European Union code number is E967. Replacing
sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...
with xylitol in food products may promote better dental health, but evidence is lacking on whether xylitol itself prevents
dental cavities Tooth decay, also known as caries,The word 'caries' is a mass noun, and is not a plural of 'carie'.'' is the breakdown of teeth due to acids produced by bacteria. The resulting cavities may be a number of different colors, from yellow to black ...
. In the United States, xylitol is used as a common
sugar substitute A sugar substitute or artificial sweetener, is a food additive that provides a sweetness like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie () or low-calorie sweetener. Arti ...
, and is considered to be safe for humans. Xylitol can be toxic to dogs and ferrets.


History

Emil Fischer Hermann Emil Louis Fischer (; 9 October 1852 – 15 July 1919) was a German chemist and List of Nobel laureates in Chemistry, 1902 recipient of the Nobel Prize in Chemistry. He discovered the Fischer esterification. He also developed the Fisch ...
, a German chemist, and his assistant Rudolf Stahel isolated a new compound from
beech Beech (genus ''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to subtropical (accessory forest element) and temperate (as dominant element of Mesophyte, mesophytic forests) Eurasia and North America. There are 14 accepted ...
wood chips in September 1890 and named it , after the Greek word for wood. The following year, the French chemist M. G. Bertrand isolated xylitol syrup by processing wheat and oat straw. Sugar rationing during
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
led to an interest in
sugar substitutes A sugar substitute or artificial sweetener, is a food additive that provides a sweetness like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie () or low-calorie sweetener. Arti ...
. Interest in xylitol and other polyols became intense, leading to their
characterization Characterization or characterisation is the representation of characters (persons, creatures, or other beings) in narrative and dramatic works. The term character development is sometimes used as a synonym. This representation may include dire ...
and manufacturing methods.


Structure, production, commerce

Xylitol is one of three 5-carbon sugar alcohols. The others are arabitol and ribitol. These three compounds differ in the stereochemistry of the three secondary alcohol groups. Xylitol occurs naturally in small amounts in plums, strawberries, cauliflower, and pumpkin; humans and many other animals make trace amounts during
metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
of
carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...
s. Unlike most sugar alcohols, xylitol is achiral. Most other
isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...
s of pentane-1,2,3,4,5-pentol are chiral, but xylitol has a plane of symmetry. Industrial production starts with
lignocellulosic biomass Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels. It is composed of two kinds of carbohydrate polymers, cellulose ...
from which xylan is extracted; raw biomass materials include
hardwood Hardwood is wood from Flowering plant, angiosperm trees. These are usually found in broad-leaved temperate and tropical forests. In temperate and boreal ecosystem, boreal latitudes they are mostly deciduous, but in tropics and subtropics mostl ...
s, softwoods, and agricultural waste from processing maize, wheat, or rice. The mixture is hydrolyzed with acid to give xylose. The xylose is purified by
chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it ...
. Purified xylose is catalytically hydrogenated into xylitol using a Raney nickel catalyst. The conversion changes the sugar (xylose, an aldehyde) into the primary alcohol, xylitol. Xylitol can also be obtained by
industrial fermentation Industrial fermentation is the intentional use of fermentation in manufacturing processes. In addition to the mass production of fermented foods and drinks, industrial fermentation has widespread applications in chemical industry. Commodity ch ...
, but this methodology is not as economical as the acid hydrolysis/chromatography route described above. Fermentation is effected by bacteria, fungi, or yeast, especially '' Candida tropicalis''. According to the US Department of Energy, xylitol production by
fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...
from discarded
biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...
is one of the most valuable renewable chemicals for commerce, forecast to be a US $1.41 billion industry by 2025.


Uses

Xylitol is used as a sugar substitute in such manufactured products as
drug A drug is any chemical substance other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect. Consumption of drugs can be via insufflation (medicine), inhalation, drug i ...
s,
dietary supplement A dietary supplement is a manufactured product intended to supplement a person's diet by taking a pill (pharmacy), pill, capsule (pharmacy), capsule, tablet (pharmacy), tablet, powder, or liquid. A supplement can provide nutrients eithe ...
s, confections,
toothpaste Toothpaste is a paste or gel dentifrice that is used with a toothbrush to clean and maintain the aesthetics of Human tooth, teeth. Toothpaste is used to promote oral hygiene: it is an abrasive that aids in removing dental plaque and food from th ...
, and
chewing gum Chewing gum is a soft, cohesive substance designed to be chewed without being swallowed. Modern chewing gum is composed of gum base, sweeteners, softeners/plasticizers, flavors, colors, and, typically, a hard or powdered polyol coating. Its tex ...
, but is not a common household sweetener. Xylitol has negligible effects on
blood sugar The blood sugar level, blood sugar concentration, blood glucose level, or glycemia is the measure of glucose concentrated in the blood. The body tightly regulates blood glucose levels as a part of metabolic homeostasis. For a 70 kg (1 ...
because its assimilation and metabolism are independent of
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the insulin (''INS)'' gene. It is the main Anabolism, anabolic hormone of the body. It regulates the metabol ...
. It is approved as a food additive and sugar substitute in the United States. Xylitol is also found as an additive to saline solution for nasal irrigation and has been reported to be effective in improving symptoms of chronic
sinusitis Sinusitis, also known as rhinosinusitis, is an inflammation of the mucous membranes that line the sinuses resulting in symptoms that may include production of thick nasal mucus, nasal congestion, facial congestion, facial pain, facial pressure ...
. Xylitol can also be incorporated into fabrics to produce a cooling fabric. When moisture, such as sweat, comes into contact with the xylitol embedded in the fabric, it produces a cooling sensation.


Food properties


Nutrition, taste, and cooking

Humans absorb xylitol more slowly than sucrose, and xylitol supplies 40% fewer calories than an equal mass of sucrose. Xylitol has about the same sweetness as
sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...
, but is sweeter than similar compounds like
sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alco ...
and mannitol. Xylitol is stable enough to be used in baking, but because xylitol and other polyols are more heat-stable, they do not caramelise as sugars do. When used in foods, they lower the freezing point of the mixture.


Food risks

No serious health risk exists in most humans for normal levels of consumption. The
European Food Safety Authority The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002 ...
has not set a limit on daily intake of xylitol. Due to the adverse laxative effect that all polyols have on the digestive system in high doses, xylitol is banned from soft drinks in the
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
. Similarly, due to a 1985 report by the E.U. Scientific Committee on Food which states that "ingesting 50 g a day of xylitol can cause
diarrhea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...
", tabletop sweeteners (as well as other products containing xylitol) are required to display the warning "Excessive consumption may induce laxative effects".


Metabolism

Xylitol has 2.4 kilocalories of
food energy Food energy is chemical energy that animals and humans derive from food to sustain their metabolism and muscular activity. Most animals derive most of their energy from aerobic respiration, namely combining the carbohydrates, fats, and protein ...
per gram of xylitol (10 kilojoules per gram) according to U.S. and E.U. food-labeling regulations. The real value can vary, depending on metabolic factors. Primarily, the liver metabolizes absorbed xylitol. The main metabolic route in humans occurs in
cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...
, via nonspecific NAD-dependent dehydrogenase (polyol dehydrogenase), which transforms xylitol to -xylulose. Specific xylulokinase phosphorylates it to -xylulose-5-phosphate. This then goes to pentose phosphate pathway for further processing. About 50% of eaten xylitol is absorbed via the intestines. Of the remaining 50% that is not absorbed by the intestines, in humans, 50–75% of the xylitol remaining in the gut is fermented by gut bacteria into short-chain organic acids and gases, which may produce
flatulence Flatulence is the expulsion of gas from the Gastrointestinal tract, intestines via the anus, commonly referred to as farting. "Flatus" is the medical word for gas generated in the stomach or bowels. A proportion of intestinal gas may be swal ...
. The remnant unabsorbed xylitol that escapes fermentation is excreted unchanged, mostly in feces; less than 2 g of xylitol out of every 100 g ingested is excreted via urine. Xylitol ingestion also increases motilin secretion, which may be related to xylitol's ability to cause diarrhea. The less-digestible but fermentable nature of xylitol also contributes to constipation relieving effects.


Health effects


Dental care

A 2015 Cochrane review of ten studies between 1991 and 2014 suggested a positive effect in reducing tooth decay of xylitol-containing
fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an Inorganic chemistry, inorganic, Monatomic ion, monatomic Ion#Anions and cations, anion of fluorine, with the chemical formula (also written ), whose ...
toothpastes when compared to fluoride-only toothpaste, but there was insufficient evidence to determine whether other xylitol-containing products can prevent tooth decay in infants, children or adults. Subsequent reviews support the belief that xylitol can suppress the growth of pathogenic Streptococcus in the mouth, thereby reducing dental cavities and gingivitis, although there is concern that swallowed xylitol may cause intestinal dysbiosis. A 2022 review suggested that xylitol-containing
chewing gum Chewing gum is a soft, cohesive substance designed to be chewed without being swallowed. Modern chewing gum is composed of gum base, sweeteners, softeners/plasticizers, flavors, colors, and, typically, a hard or powdered polyol coating. Its tex ...
decreases plaque, but not xylitol-containing candy.


Earache

In 2011 EFSA "concluded that there was not enough evidence to support" the claim that xylitol-sweetened gum could prevent middle-ear infections, also known as acute otitis media (AOM). A 2016 review indicated that xylitol in chewing gum or a syrup may have a moderate effect in preventing AOM in healthy children. It may be an alternative to conventional therapies (such as
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...
s) to lower risk of earache in healthy children – reducing risk of occurrence by 25%  – although there is no definitive proof that it could be used as a therapy for earache.


Diabetes

In 2011, EFSA approved a marketing claim that foods or beverages containing xylitol or similar sugar replacers cause lower blood glucose and lower
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the insulin (''INS)'' gene. It is the main Anabolism, anabolic hormone of the body. It regulates the metabol ...
responses compared to sugar-containing foods or drinks. Xylitol products are used as
sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...
substitutes for weight control, as xylitol has 40% fewer calories than sucrose (2.4 kcal/g compared to 4.0 kcal/g for sucrose). The
glycemic index The glycemic (glycaemic) 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 ...
(GI) of xylitol is only 7% of the GI for
glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...
.


Adverse effects


Humans

When ingested at high doses, xylitol and other polyols may cause
gastrointestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...
discomfort, including
flatulence Flatulence is the expulsion of gas from the Gastrointestinal tract, intestines via the anus, commonly referred to as farting. "Flatus" is the medical word for gas generated in the stomach or bowels. A proportion of intestinal gas may be swal ...
,
diarrhea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...
, and
irritable bowel syndrome Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating, and changes in the consistency of bowel movements. These symptoms may ...
(see
Metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
above); some people experience the adverse effects at lower doses. Xylitol has a lower laxation threshold than some sugar alcohols but is more easily tolerated than mannitol and
sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alco ...
. Increased xylitol consumption can increase oxalate, calcium, and phosphate excretion to urine (termed '' oxaluria'', '' calciuria'', and '' phosphaturia'', respectively). These are known risk factors for
kidney stone disease Kidney stone disease (known as nephrolithiasis, renal calculus disease, or urolithiasis) is a crystallopathy and occurs when there are too many minerals in the urine and not enough liquid or hydration. This imbalance causes tiny pieces of cry ...
, but despite that, xylitol has not been linked to kidney disease in humans.


Dogs and other animals

Xylitol is poisonous to dogs. Ingesting 100 milligrams of xylitol per kilogram of body weight (mg/kg bw) causes dogs to experience a dose-dependent
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the insulin (''INS)'' gene. It is the main Anabolism, anabolic hormone of the body. It regulates the metabol ...
release; depending on the dose it can result in life-threatening
hypoglycemia Hypoglycemia (American English), also spelled hypoglycaemia or hypoglycæmia (British English), sometimes called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's tria ...
. Hypoglycemic symptoms of xylitol toxicity may arise as quickly as 30 to 60 minutes after ingestion. Vomiting is a common first symptom, which can be followed by tiredness and
ataxia Ataxia (from Greek α- negative prefix+ -τάξις rder= "lack of order") is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in e ...
. At doses above 500 mg/kg bw, liver failure is likely and may result in coagulopathies like
disseminated intravascular coagulation Disseminated intravascular coagulation (DIC) is a condition in which blood clots form throughout the body, blocking Microvessel, small blood vessels. Symptoms may include chest pain, shortness of breath, leg pain, problems speaking, or problems ...
. It is also poisonous to ferrets. Xylitol is safe for
rhesus macaque The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies split between two groups, the Chinese-derived and the Indian-derived. Generally brown or g ...
s,
horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...
s, and rats. A 2018 study suggests that xylitol is safe for cats in doses of up to 1000 mg/kg; however, this study was performed on only 6 cats and should not be considered definitive. The ASPCA has never issued any warning about xylitol and cats. A 2022 ASPCA article explicitly lists xylitol as non-toxic.


See also

*
Aspartame Aspartame is an artificial non-saccharide sweetener commonly used as a sugar substitute in foods and beverages. 200 times sweeter than sucrose, it is a methyl ester of the aspartic acid/phenylalanine dipeptide with brand names NutraSwe ...
* Birch sap * -Xylulose reductase * Xylonic acid


References


External links

* {{Authority control Chewing gum E-number additives Excipients Sugar alcohols Sugar substitutes Veterinary toxicology