Does xylitol break a fast?

Xylitol is a sugar alcohol (polyol) sold as a granulated sweetener and used in sugar-free gum, mints and toothpaste. EU labelling rules count polyols such as xylitol at 2.4 kcal per gram, against 4 kcal per gram for sugar. A 4 g teaspoon has about 10 kcal, and one xylitol label lists 20 kcal for 2 teaspoons (8 g). Erythritol, another sugar alcohol, counts as 0 kcal per gram.

This site sorts answers by four goals. For weight loss, a teaspoon of xylitol is a grey area. Its 10 kcal is under the common 50-calorie rule of thumb, which is not an official limit. It is still a sweet taste with real calories. For autophagy it breaks a fast, because the strictest goal counts anything with calories. Blood sugar is grey. Xylitol is a carbohydrate with calories, so the database does not mark it safe the way it marks erythritol. Gut rest is grey because large amounts can cause wind and diarrhoea.

The laxative effect depends on how much you have. In the EU, foods with more than 10% added polyols must carry the warning "excessive consumption may produce laxative effects". As a worked example, a teaspoon in each of three coffees adds about 30 kcal and 12 g of xylitol across a fasting morning. Count the xylitol in gum and mints as well as the spoonfuls in your drinks.

Xylitol is poisonous to dogs. In a dog it can make blood sugar drop fast, and that can be life-threatening. Keep xylitol, sugar-free gum and mints out of a dog's reach, and call a vet straight away if one may have eaten some. If you take medicine for diabetes, ask your doctor before you start fasting.