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Updated April 30, 2015.

Look on the label of a sugar-free candy, and you're likely to see words like maltitol, xylitol, and sorbitol. These are sugar alcohols. However, they aren't actually sugar or alcohol. So what are these substances and how will they affect your body?

What are sugar alcohols?

Sugar alcohols are a type of carbohydrates called "polyols". Part of their chemical structure resembles sugar, and part of it resembles alcohol -- hence the confusing name.

Examples of common sugar alcohols are maltitol, sorbitol, isomalt, and xylitol.

Where do sugar alcohols come from?

Sugar alcohols occur naturally in plants. Some of them are extracted from plants (sorbitol from corn syrup and mannitol from seaweed), but they are mostly manufactured from sugars and starches.

Why use sugar alcohols?

Sugar alcohols are like sugar in some ways, but they are not completely absorbed by the body. Because of this, the blood sugar impact of sugar alcohols is less and they provide fewer calories per gram. Additionally, sugar alcohols don't promote tooth decay as sugars do, so are often used to sweeten chewing gum. One, xylitol, actually inhibits bacterial growth in the mouth.

It's important to note, however, that the different types of sugar alcohols act very differently in the body (see chart below).

Can sugar alcohols cause problems?

Though the word "alcohol" is part of their name, they cannot get you drunk. But because they are not completely absorbed, they can ferment in the intestines and cause bloating, gas, or diarrhea.

People can have different reactions to different sugar alcohols. Careful experimentation is advised.

How are sugar alcohols labeled?

The names of the individual sugar alcohols will be on the ingredient list of any product that contains them. They will be included in the amount of carbohydrate on the label, either in the total or on a separate line for sugar alcohols. If the product is labeled “sugar-free” or "no added sugar," the manufacturer must show the sugar alcohol count separately.

How do sugar alcohols compare to other carbohydrates?

Though sugar alcohols have fewer calories than sugar, most of them aren't as sweet, so more must be used to get the same sweetening effect. A good example is maltitol, which has 75% of the blood sugar impact of sugar, but also only 75% of the sweetness. So they end up being equal in that regard. Still, there is a range of sweetness and impact on blood sugar among the sugar alcohols.

This chart compares the different polyols.

GI=glycemic index

Cal/g=Calories per gram

Bear in mind that the glycemic index is a range, rather than a fixed number. Different studies yield different results. This chart is mainly sourced by the Livesey research reported in Nutrition Research Reviews, December 2003.
Comparison of Sugar and Sugar Alcohols

Ingredient	Sweetness	GI	Cal/g
Sucrose(sugar)	100%	60	4
Maltitol Syrup	75%	52	3
Hydrogenated Starch Hydrolysate	33%	39	2.8
Maltitol	75%	36	2.7
Xylitol	100%	13	2.5
Isomalt	55%	9	2.1
Sorbitol	60%	9	2.5
Lactitol	35%	6	2
Mannitol	60%	0	1.5
Erythritol	70%	0	0.2