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A sugar alcohol (also known as a polyol, polyhydric alcohol, or polyalcohol) is a hydrogenated form of carbohydrate, whose carbonyl group (aldehyde or ketone, reducing sugar) has been reduced to a primary or secondary hydroxyl group. Its general formula is H(HCHO)_n+1H, whereas sugar's is H(HCHO)_nHCO. They are commonly used for replacing sucrose in foodstuffs, often in combination with high intensity artificial sweeteners to counter the low sweetness. Furthermore, they do not contribute to tooth decay.

Some common sugar alcohols:

Disaccharides and monosaccharides can both form sugar alcohols; however, sugar alcohols derived from disaccharides (e.g. maltitol and lactitol) are not entirely hydrogenated because only one aldehyde group is available for reduction.

Sugar alcohols as food additives

Source: Antonio Zamora, "Carbohydrates"

Name	Sweetness over sucrose	Caloric content (kcal/g)	Sweetness per caloric content
Arabitol	0.7	0.2	3.5
Erythritol	0.812	0.213	3.498
Glycerol	0.6	4.3	0.14
HSH	0.4–0.9	3.0	0.13–0.3
Isomalt	0.5	2.0	0.25
Lactitol	0.4	2.0	0.2
Maltitol	0.9	2.1	0.43
Mannitol	0.5	1.6	0.31
Sorbitol	0.6	2.6	0.23
Xylitol	1.0	2.4	0.42
Compare with: Sucrose	1.0	4.0	0.25

As a group, sugar alcohols are not as sweet as sucrose, and they are also less caloric than sucrose. Their flavor is like sucrose, and they can be used to mask the unpleasant aftertastes of some high intensity sweeteners. In addition to their sweetness, some sugar alcohols can produce a noticeable cooling sensation in the mouth when highly concentrated, for instance in sugar-free hard candy ("boiled sweets") or chewing gum. This cooling sensation is due to the dissolving of the sugar alcohol into solution being an endothermic (heat-absorbing) reaction. Sugar alcohols are not metabolized by oral bacteria, and so they do not contribute to tooth decay. They do not brown and caramelize when heated.

Sugar alcohols are usually incompletely absorbed into the blood stream from the small intestines which generally results in a smaller change in blood glucose than "regular" sugar (sucrose). This property makes them popular sweeteners among diabetics and people on low-carbohydrate diets. However, as for many other incompletely digestible substances (such as dietary fiber), overconsumption of sugar alcohols can lead to bloating, diarrhea and flatulence because they are not absorbed in the small intestine. Some individuals experience such symptoms even in a single-serving quantity. With continued use, most people develop a degree of tolerance to sugar alcohols and no longer experience these symptoms. As an exception, erythritol is actually absorbed in the small intestine and excreted unchanged through urine, so it has no side effects at typical levels of consumption.

The table above presents the relative sweetness and measured caloric content of the most widely-used sugar alcohols. Despite the variance in caloric content of sugar alcohols, EU labeling requirements assign a blanket value of 2.4 kcal/g to all sugar alcohols.

People who have undergone gastric bypass surgery, specifically Roux-en-Y (RGB), should be careful not to eat too many sugar alcohols as doing so can lead to "dumping".^{[citation needed]}