Anyone who has eaten a "sugar-free" protein bar and regretted it an hour later has probably met a sugar alcohol. Ingredients like maltitol, erythritol, sorbitol, and xylitol are only partly absorbed as they pass through the small intestine, and whatever doesn't get absorbed travels on to the colon, where resident gut bacteria ferment it. That fermentation process — producing gas and pulling water into the intestine along the way — is the actual mechanism behind the bloating, gas, and laxative effect that people tend to associate with "sugar-free" and "low-sugar" products generally. Most people tolerate small amounts without noticing anything, but symptoms tend to start showing up somewhere between 10 and 20 grams, with the exact threshold depending on which sugar alcohol it is and how sensitive an individual's gut happens to be.
This article works through what sugar alcohols actually are, why some are far more likely than others to cause a problem, and how to spot them on a label before you're three bites into a bar and starting to regret it.
What Exactly Is a Sugar Alcohol?
Despite the name, a sugar alcohol is neither sugar nor alcohol in the way most people think of either term — the name comes from a chemical structure that resembles both a sugar molecule and an alcohol molecule, without behaving fully like either one. They do occur naturally in small amounts in some fruits and vegetables, but the sugar alcohols found in packaged food are almost always manufactured, simply because natural sources don't provide anywhere near enough concentration to sweeten a product at commercial scale.
Food manufacturers reach for them because they add both sweetness and bulk with fewer calories and a smaller blood sugar impact than table sugar carries. That's precisely why they turn up so often in products marketed as "sugar-free," "reduced sugar," or "keto," and protein bars are one of the categories where they appear most consistently.
The Most Common Sugar Alcohols, and How They Differ
Not every sugar alcohol behaves the same way once it's inside you, and the differences between them are large enough to matter. Erythritol is generally the best tolerated of the group — most of it is actually absorbed in the small intestine rather than passing through to the colon, and what is absorbed gets excreted unchanged in urine, so relatively little of it ever reaches the bacteria that would ferment it. It also carries a glycemic index close to zero, meaning it does almost nothing to blood sugar, and most people can tolerate 50 grams or more before noticing any digestive effect. You'll typically find it in "zero sugar" bars, keto baking, and drink mixes.
Xylitol, common in sugar-free gum, mints, and some bars, sits in the middle of the pack: a modest glycemic index of roughly 7 to 13, and a digestive tolerance threshold in the range of 20 to 30 grams for most people. Sorbitol, found in sugar-free candy and some bars and syrups, has a low glycemic index but a tighter tolerance window of around 10 to 20 grams. Maltitol is the one worth watching most closely — it shows up constantly in sugar-free chocolate and many reduced-sugar bars, but it carries a glycemic index of about 35, roughly half that of table sugar, and it's the sugar alcohol most likely to cause noticeable bloating and diarrhea, often at the same 10-to-20-gram threshold where sorbitol starts causing problems. Mannitol, less common but still found in some sugar-free gum, has a glycemic index near zero but a surprisingly low tolerance threshold — some people notice digestive effects even in small amounts. For reference, table sugar itself carries a glycemic index of roughly 60 to 70, which is the benchmark all of these ingredients are being compared against when a label claims a "low glycemic" or "sugar-free" profile.
Why Do They Cause Gas, Bloating, and a Laxative Effect?
Two separate mechanisms are happening at once, and together they explain almost everything about how a sugar alcohol makes you feel. First, whatever portion of the sugar alcohol isn't absorbed draws water into the intestine through simple osmosis, which produces a mild laxative effect — this is the same underlying principle that makes sorbitol effective as an actual laxative in some over-the-counter products. Second, gut bacteria living in the colon ferment the leftover sugar alcohol that made it that far, and that fermentation produces gas — carbon dioxide, hydrogen, and sometimes methane — as a natural byproduct. Together, the osmotic water pull and the bacterial fermentation are what show up as bloating, cramping, and, at higher intakes, diarrhea.
There's a broader category worth knowing here too: sugar alcohols fall under the "P" in FODMAP, the acronym for fermentable oligo-, di-, mono-saccharides and polyols. That classification means people with irritable bowel syndrome or a generally sensitive gut often react to sugar alcohols at meaningfully smaller amounts than the general population would.
Do Sugar Alcohols Affect Blood Sugar?
Less than table sugar, generally, but not always as little as the marketing implies. Erythritol and mannitol both carry a glycemic index close to zero and barely move blood sugar at all. Xylitol is low but not zero. Maltitol is the outlier worth flagging specifically — despite being one of the most common ingredients used to create "sugar-free" claims, it carries a glycemic index of roughly 35, which is still enough to produce a noticeable blood sugar rise if a bar is sweetened primarily with it.
This distinction matters for the "net carb" math that shows up on a lot of low-carb and keto product labels. Many of those products subtract the entire sugar alcohol content from total carbohydrates, on the assumption that none of it gets absorbed. For erythritol, that assumption is close enough to accurate to be reasonable. For maltitol and sorbitol, it overstates how metabolically "free" those carbohydrates actually are.
How to Spot Sugar Alcohols on a Label
Most sugar alcohol ingredient names end in "-itol" — erythritol, xylitol, maltitol, sorbitol, mannitol, isomalt, and lactitol cover the ones you're most likely to encounter. On a Canadian or U.S. nutrition panel, they're typically broken out on a line labelled "sugar alcohol" underneath total carbohydrates, which makes them easy to check for once you know to look. If a product is labelled "sugar-free," "no added sugar," or "keto," it's worth glancing at that line before eating a full serving in one sitting, particularly if you're sensitive to FODMAPs or trying the product for the first time.
One safety note that has nothing to do with human digestion but is worth knowing regardless: xylitol is highly toxic to dogs, even in relatively small amounts. Anyone with a dog in the house should keep sugar-free gum and other xylitol-sweetened products well out of reach.
Why Good Protein Skips Sugar Alcohols Entirely
Rather than trying to pick the sugar alcohol that causes the fewest complaints, Good Protein leaves all of them out of the formula — no maltitol, erythritol, sorbitol, mannitol, or xylitol. Its taste and texture come from the recipe itself rather than from a sugar substitute, which removes one entire variable that can otherwise turn a snack into a stomach ache. The bar still lands at 200 calories with 20 grams of complete soy protein, 4 grams of BCAAs, and 7 grams of fibre — the low-sugar profile just isn't achieved by leaning on a polyol.
Common Questions About Sugar Alcohols
Whether sugar alcohols are "bad for you" is probably the most common question, and the honest answer is that they're generally recognized as safe for most people in moderate amounts — the real downside is digestive discomfort above your personal tolerance threshold, not a broader health risk. On blood sugar, some sugar alcohols barely register at all, erythritol and mannitol in particular, while others like maltitol, sorbitol, and xylitol have a partial effect; none of them spike blood sugar the way table sugar does, but "sugar-free" doesn't automatically mean zero impact. On keto-friendliness, most sugar alcohols fit reasonably well, but not equally — erythritol comes closest to a true zero-impact sweetener, while maltitol's real glycemic effect makes it a weaker fit despite how often it appears in products carrying a "net carb" label. As for which one causes the least bloating, erythritol is typically the best tolerated, since most of it gets absorbed before it ever reaches the colon, while maltitol tends to cause the most complaints. And on how much is actually safe in one sitting, it depends on the type and the person, but symptoms commonly start in the 10-to-20-gram range for sorbitol and maltitol, somewhat higher for xylitol, and considerably higher for erythritol — checking the label and starting with a smaller portion is the simplest way to find your own tolerance.
Looking for a protein bar that skips sugar alcohols altogether? Explore Good Protein — 20g complete soy protein, 4g BCAAs, and zero sugar alcohols in every bar.
