Sugar alcohols on keto: why maltitol is a trap (and which sweeteners are fine)

Sugar alcohols on keto are a mixed bag. Erythritol barely moves blood sugar and is usually fine to subtract from your carb count. Maltitol, the cheap one used in most "sugar-free" chocolate and candy, has a glycemic index of about 35, roughly half that of table sugar, according to a major review of polyols. That is why a bag of sugar-free gummies can quietly stall ketosis even when the front of the pack says "0 g sugar." The rule: find out which sugar alcohol you are eating before you subtract anything.

What sugar alcohols actually are

Sugar alcohols (polyols) are carbohydrates with a slightly different chemical structure from sugar. They are not alcohol in the drinking sense. The common ones are erythritol, xylitol, sorbitol, mannitol, isomalt, lactitol, maltitol and maltitol syrup (also called polyglycitol or hydrogenated starch hydrolysates).

Three facts matter for keto:

1. They are carbs on the label. Under US rules, total carbohydrate is calculated by difference, so sugar alcohols sit inside the "Total carbohydrate" number (21 CFR 101.9).
2. Declaring them is voluntary. A "Sugar alcohol" line is optional unless the package makes a claim about sugar or sugar alcohols. Many products do list them because they want you to subtract them.
3. "Net carbs" is not a regulated term. There is no FDA formula for it. When a package says "2 g net carbs," the brand decided what to subtract. We cover that in keto-friendly label traps.

The glycemic index of each sugar alcohol

The best single source here is Geoffrey Livesey's review in Nutrition Research Reviews, which pooled the published data. On a scale where glucose is 100 and sucrose (table sugar) is 65:

The same review gives insulin index values in the same order: erythritol 2, xylitol 11, sorbitol 11, maltitol 27 and polyglycitol 23, against 43 for sucrose. So maltitol does not just raise glucose, it raises insulin too, and lower insulin is the thing that lets ketone production ramp up.

Why maltitol is the trap

Maltitol is the most common sweetener in mass-market "sugar-free" chocolate, cookies, gummies and hard candy for a simple reason: it behaves a lot like sugar in a recipe. It browns, it melts, it tastes clean. It also behaves a bit like sugar in your body.

The trap works like this:

• The front says "Sugar free", which legally only means less than 0.5 g of sugars per serving (21 CFR 101.60). Maltitol is not a "sugar" for that rule.
• The back lists, say, 20 g total carbs and 15 g sugar alcohols.
• A net-carb badge subtracts all 15 g, so you see "5 g net."
• But with a glycemic index around half of sugar, those 15 g of maltitol act more like 7 or 8 g of sugar. Your real impact is closer to 12 g than 5 g, per serving, and the serving is often small.

USDA data shows the scale of it. Sugar-free peanut butter cookies come in at about 13.7 g net carbs per three cookies even with 0 g sugar listed (USDA FoodData Central). A single sorbitol-sweetened "dietetic" hard candy is about 3 g of carbohydrate (USDA).

Figures from USDA FoodData Central SR Legacy, total carbohydrate minus fiber. Brands differ, so check your product.

Watch out: If the ingredient list says "maltitol," "maltitol syrup," "hydrogenated starch hydrolysate" or "polyglycitol," do not subtract the sugar alcohols in full. Count at least half, and if you are strict or testing your response, count them all.

Erythritol: the keto favorite, with one caveat

Erythritol has a glycemic index of about 0 and is mostly absorbed and then excreted unchanged in urine. For blood sugar, it is about as close to free as a sweetener gets, and it causes fewer stomach problems than the others at normal doses.

The caveat is a 2023 study in Nature Medicine from Cleveland Clinic researchers. In more than 1,000 people undergoing cardiac risk assessment, and then in US and European validation groups, higher blood erythritol was associated with a higher three-year risk of heart attack, stroke or death. In lab and animal tests, erythritol made platelets more prone to clotting. When eight healthy volunteers drank 30 g of erythritol (which the authors compare to a pint of keto ice cream), their blood levels rose about a thousandfold and stayed raised for more than two days.

The authors are clear that the human data show association, not causation. It is not a reason to panic about a little erythritol in your coffee. It is a reason not to build your diet around erythritol-sweetened desserts, and to talk to your doctor if you have heart disease or clotting risk.

Xylitol and sorbitol: small effect, real side effects

Xylitol (GI about 13) and sorbitol (GI about 9) raise blood sugar a little. In normal gum-and-mint amounts they rarely matter for ketosis. In baked goods made with cups of xylitol, they start to.

Two cautions:

• Heart signal. A 2024 study from the same research group, summarized by the NIH, found a similar pattern for xylitol: higher blood levels linked to heart events, and increased platelet activity after a xylitol drink. Again, early evidence, but consistent.
• Dogs. The FDA warns that xylitol can poison dogs, causing low blood sugar, seizures and liver damage, sometimes from just a few pieces of gum. If you bake keto with xylitol and have a dog, store it like medicine.

The gut problem

Most sugar alcohols are only partly absorbed. What is not absorbed reaches the large intestine, pulls in water and gets fermented. The result is gas, bloating and, in larger amounts, diarrhea. FDA rules require foods likely to deliver 50 g of sorbitol a day to carry the warning "Excess consumption may have a laxative effect" (21 CFR 184.1835). Maltitol is notorious for this in sugar-free candy, where one serving is small and the bag is not.

Bunny tip: Treat "sugar-free" sweets like regular sweets: one portion, on a plate, not straight from the bag. You will dodge both the carb creep and the bathroom sprint.

Non-sugar-alcohol sweeteners that work on keto

These are not polyols but come up in the same aisle:

• Allulose is a rare sugar. The FDA lets brands leave it out of "Total sugars" and "Added sugars" and count it at 0.4 calories per gram, because it is barely metabolized and has a negligible glucose effect. It still counts in total carbohydrate on the label, so you may need to subtract it yourself.
• Stevia and monk fruit. The FDA has not questioned GRAS status for certain highly purified steviol glycosides and monk fruit extracts. They are used in tiny amounts, so they add almost no carbs themselves.
• Sucralose, aspartame, saccharin, acesulfame K are FDA-approved high-intensity sweeteners with negligible carbs in the pure form.

The catch with all of these is the filler. Packets and "baking blends" often bulk up the sweetener with dextrose, maltodextrin or even sugar. A Splenda packet is about 0.9 g of carbohydrate per packet in USDA data, though the label rounds it to zero. That matters only if you use many packets, but it adds up in the same way as the other hidden carbs we list here.

How to count sugar alcohols on keto

There is no official method, so here is a cautious, practical one:

1. Read the ingredient list first. Identify every sweetener.
2. Erythritol or allulose only: subtract them fully from total carbs (after fiber).
3. Xylitol, sorbitol, isomalt: subtract about half, and watch your own response.
4. Maltitol or maltitol syrup: count at least half, ideally all.
5. "Sugar alcohols" with no name, or a blend: count them all.
6. Then multiply by the servings you actually eat.

If you test with a blood ketone meter, try a new sweetener on its own and check whether your reading drops a couple of hours later; our guide on how to know you're in ketosis covers testing. If you have diabetes, especially on insulin or sulfonylureas, check with your doctor before relying on sugar-free products, since your glucose response may differ from these averages.

Track it with KetoBunny: Log a sugar-free treat with a photo and KetoBunny breaks out total and net carbs and folds it into your daily ketosis estimate, so you can see whether that "2 g net" bar is really costing you more.

The bottom line

Sugar alcohols are not a free pass and not a villain. Erythritol is close to neutral for blood sugar, with an open question about heavy use and heart risk. Xylitol and sorbitol are fine in small amounts if your gut agrees. Maltitol is the trap: it is in most cheap sugar-free sweets, it raises blood sugar and insulin, and labels that subtract it fully are flattering themselves. Read the ingredient list, count maltitol, and keep sugar-free treats as treats.