Sugar alcohols are reduced-calorie sweeteners that give protein bars their sweet taste without the full sugar load. They’re a type of carbohydrate derived from sugars, but your body absorbs them differently, which means fewer calories and a smaller blood sugar spike. The most common ones you’ll find in protein bars are erythritol, maltitol, sorbitol, and xylitol, though the FDA has approved eight total for use in food.
How Sugar Alcohols Work
Despite the name, sugar alcohols contain neither sugar nor alcohol in the way you’d normally think of them. They’re carbohydrates that have been chemically modified so that a specific part of their molecular structure is replaced with a different chemical group. This small change has a big practical effect: your small intestine absorbs them slowly and incompletely compared to regular sugar.
That incomplete absorption is the whole point. Regular sugar delivers about 4 calories per gram. Sugar alcohols range from 0 calories per gram (erythritol) to 3 calories per gram (hydrogenated starch hydrolysates), with most landing around 2 to 2.6 calories per gram. That’s roughly half to two-thirds the calories of sugar for a comparable level of sweetness.
Some sugar alcohols also occur naturally in foods. Sorbitol is found in apples, pears, peaches, and apricots. Erythritol shows up in mushrooms, fermented foods like wine and soy sauce, and certain fruits and vegetables. But the amounts in protein bars are produced synthetically, typically from sugars themselves.
Why Protein Bar Makers Use Them
Sugar alcohols solve several problems at once for protein bar manufacturers. First, they can replace sugar at roughly a 1:1 ratio, providing the same bulk and volume. This matters because artificial sweeteners like sucralose are hundreds of times sweeter than sugar and can’t fill the same physical role in a bar. You need something that takes up space, and sugar alcohols do that.
They also act as humectants, meaning they retain moisture and keep bars from drying out and turning into bricks on the shelf. This extends shelf life and improves texture. On top of that, they’re often blended with other sweeteners to fine-tune the taste, since some sugar alcohols on their own have a cooling sensation or slightly different flavor profile than sugar.
For brands marketing to low-carb or keto consumers, sugar alcohols let them advertise impressively low “net carb” numbers on the front of the package, which is a major selling point.
Blood Sugar and Insulin Effects
The blood sugar impact varies dramatically depending on which sugar alcohol is in your bar. Regular sugar (sucrose) has a glycemic index of 65 to 69. Here’s how the common sugar alcohols compare:
- Erythritol: glycemic index of 0, essentially no effect on blood sugar or insulin
- Xylitol: glycemic index of 13
- Sorbitol: glycemic index of 9
- Maltitol: glycemic index of 35, the highest of the group
- Isomalt: glycemic index of 9
- Mannitol: glycemic index of 0
Maltitol deserves special attention because it’s one of the most commonly used sugar alcohols in protein bars, yet it has a glycemic index of 35 and an insulin index of 27. That’s still lower than sugar, but it’s not negligible. If you’re managing diabetes or strictly tracking blood sugar, a bar sweetened with maltitol will affect you noticeably more than one using erythritol. Check the ingredient list, not just the front-of-package claims.
The “Net Carbs” Calculation
You’ve probably seen protein bars advertising “4g net carbs” while the nutrition label shows 25 or 30 grams of total carbohydrates. The difference is almost always sugar alcohols. “Net carbs” isn’t an FDA-regulated term. It’s a marketing concept based on the idea that sugar alcohols don’t fully count as carbohydrates because your body doesn’t fully absorb them.
The standard approach, recommended by the UCSF Diabetes Teaching Center, is to subtract half the grams of sugar alcohol from total carbohydrates. So if a bar has 29 grams of total carbs and 18 grams of sugar alcohol, you’d count it as 20 grams of carbohydrate (29 minus 9). The exception is erythritol, which many people subtract entirely since it contributes zero calories and has no measurable effect on blood sugar.
This is worth knowing because some brands subtract 100% of all sugar alcohols when calculating net carbs on their packaging, which can be misleading, particularly for maltitol-heavy bars.
How to Read the Label
Under FDA rules, listing sugar alcohols on a nutrition facts panel is technically voluntary. However, if a product makes any claim about sugar content (like “sugar-free” or “no sugar added”), sugar alcohol content must be declared. Since nearly every protein bar makes some version of this claim, you’ll almost always see it listed.
Sugar alcohols appear indented under “Total Carbohydrate” on the label, similar to how dietary fiber and total sugars are listed. If only one type is used, the label can name it specifically (for example, “Erythritol 10g” instead of “Sugar Alcohol 10g”). The FDA counts sugar alcohols separately from total carbohydrate when calculating calories, using specific calorie values for each type rather than the standard 4 calories per gram applied to other carbs.
Digestive Side Effects
This is the part most protein bar eaters discover the hard way. Because sugar alcohols aren’t fully absorbed in your small intestine, a significant portion travels to your large intestine intact. Once there, two things happen. First, the unabsorbed molecules pull water into your gut through osmosis, which can cause loose stools or outright diarrhea. Second, bacteria in your colon ferment the sugar alcohols, producing gas that leads to bloating, cramping, and flatulence.
The severity depends on the type of sugar alcohol and how much you eat. Erythritol is the best tolerated because it’s mostly absorbed in the small intestine before reaching the colon. Sorbitol is one of the worst offenders: bacteria break it down into smaller molecules with even higher osmotic potential, pulling more water into the gut. Maltitol gets partially broken down into glucose (which is absorbed) and sorbitol (which largely isn’t), so it can cause problems too. Lactitol passes through the small intestine almost completely unabsorbed, making it particularly likely to cause gas and diarrhea.
The good news is that this isn’t harmful. Osmotic diarrhea from sugar alcohols is a simple physical response, not a sign of disease or damage. It resolves on its own once the sugar alcohols clear your system. Many people also build some tolerance with regular, moderate consumption. If you’re eating two or three protein bars a day, though, you’re stacking those sugar alcohol grams, and digestive distress becomes much more likely. People with irritable bowel syndrome are particularly sensitive, as sugar alcohols fall into the category of FODMAPs that can trigger symptoms.
Erythritol vs. Maltitol vs. Other Options
Not all sugar alcohols are equal, and the one in your protein bar matters. Erythritol is the standout: zero calories per gram, no blood sugar impact, and the fewest digestive side effects. It’s the smallest sugar alcohol molecule, which allows about 90% of it to be absorbed in the small intestine and excreted in urine before it ever reaches the colon. The tradeoff is that erythritol is only about 60 to 70 percent as sweet as sugar, so bars using it often need additional sweeteners.
Maltitol provides about 75 to 90 percent of sugar’s sweetness at 2.1 calories per gram, making it a popular and cost-effective choice. But its glycemic index of 35 means it does raise blood sugar meaningfully, and its partial conversion to sorbitol in the gut makes it a common culprit for digestive complaints. Xylitol lands in the middle: 2.4 calories per gram, a glycemic index of 13, and moderate digestive tolerance.
Some newer protein bars are moving away from sugar alcohols entirely, using novel sweeteners like allulose, monk fruit, or stevia instead. These plant-derived sweeteners don’t contribute meaningful calories or raise blood sugar, and they don’t carry the same digestive risks. Allulose in particular has gained traction in protein bars because, like sugar alcohols, it adds bulk and texture rather than just sweetness. If sugar alcohols consistently bother your stomach, bars using these alternatives are worth seeking out.
A Warning for Dog Owners
Xylitol is extremely toxic to dogs. When a dog eats xylitol, it triggers a massive release of insulin that can drop blood sugar to dangerous levels within 10 to 60 minutes. Symptoms include vomiting, weakness, staggering, seizures, and collapse. This can be life-threatening without emergency veterinary treatment. The FDA has issued specific warnings about xylitol and dogs. If your protein bars contain xylitol, keep them well out of reach of pets. Cats appear to be less affected, though ferrets may be at similar risk as dogs.