Sugar alcohols are not actually sugars, nor are they alcohols. They are a type of carbohydrate that don't fit neatly into any of the sub categories on a nutrition panel. Most people subtract these out of the total carb value, just like with fiber. Unfortunately for dieters, the sugar carb total is just lumped into the 'total carbs' number of a package's label, so you can't easily subtract them out like fiber.
The only way to know how many sugar alcohols are in a given total carb count is if the maker of the product tells you what the actual net carbs of the food item are, doing that work for you.
Another name for sugar alcohols are "polyols". Some common types of sugar alcohols include maltitol, sorbitol and isomalt.
Sugar alcohols are commonly used in sugar free products and diet products because they are very slow to be absorbed and do not cause the "sugar rush / blood sugar spike" that normal carbohydrates cause. Many (if not most) people do not absorb sugar alcohols at all before they pass through the system. So in essence they can give great sugar flavors without having the fat-gaining effects of regular sugars. They act like fiber, but they taste like sugar.
Such a cool, tasty result does not come without some penalty. Because sugar alcohols just slide through your digestive system, they can cause a laxitive effect if you eat too many of them. They can also cause gassiness, because the bacteria in your intestines normally don't see any carbs at all (your stomach deals with them). When your intestines run into these sugar alcohols, they go a bit crazy :) Some people get a little farty. A few people get "gastric distress" (i.e. diarrhea). If you've never tried sugar alcohols before, be sure to try them in SMALL amounts to see which group you fall into.
Do Sugar Alcohols Count?
Sugar alcohols don't cause a sugar rush, and are pretty much passed through your system. So in many ways, they are pretty much like fiber. They go in, they go out, they don't touch your blood sugar levels and don't turn into fat. You could discount them when figuring out the 'net carbs' on a food item.
But a few people DO have problems losing weight when they eat too many sugar alcohol products. Part of the theory is that their tongue tastes sweetness - and that they are still so sugar-addicted that just the TASTE of something sweet causes their body to react as if they DID eat something sweet. Exactly how or why this works, I'm not sure. But I do know people personally who stall when they eat sugar alcohol products. If they stop eating them, they lose weight again. So I would be cautious about eating too many sugar alcohols. If you find yourself stalling, remove them again and see if it has any impact.
Some people complain - if sugar alcohols cause problems, why use them? Why not just use Splenda and other sweeteners? It comes down to the technical aspects of baking. Splenda is cool - but it simply isn't sugar. There are types of cooking and baking where Splenda does not react well. These are situations where sugar alcohols work *perfectly*. So for the 99% of the population which doesn't have reactions to sugar alcohols, these products are great. If you're in the 1% that has tummy problems with sugar alcohols, you can eat the sugar-free items Splenda can be used to create. For example, sugar alcohols are commonly used in sugar free candies because they mimic sugar so nicely in the baking process.
In general, sugar alcohols and any artificial sweeteners are good ways to wean yourself off of sugar - but remember that the end result of this process should be aiming to reduce your sweet tooth in general. You should be filling your daily meal plan with healthy foods, not with sugary substitutes. So be sure to eat sugar alcohol items only occasionally, and stick with the healthy foods and meats that should be the bulk of your diet!
NOTE: I've heard from pet owners that pets can get very sick if they eat items with sugar alcohols. Please never feed these to your pets!
Lisa Shea's Library of Low Carb Books