Does sugar-free syrup break a fast?

Sugar-free syrups come in two kinds, and their labels differ. Coffee-shop style syrups, the thin ones pumped into a latte or a black coffee, are about 0 kcal per 2 tablespoons (30 ml). Sugar-free pancake syrups are thicker and have about 15 kcal per 2 tablespoons, from sugar alcohols or other carbohydrate. A quarter cup (60 ml) of one pancake syrup is about 35 kcal.

This site sorts answers by four goals. A sugar-free coffee syrup is a grey area on all four, like the other non-sugar sweeteners in the database. Its calories are close to zero. Some people say sweet tastes leave them hungrier, but the research on this is mixed. WHO advises against using non-sugar sweeteners to control body weight, as a conditional recommendation. It is still unresolved whether sweeteners raise insulin, and the answer may differ from person to person. That is why autophagy and blood sugar are grey. Gut rest is grey because the syrup brings sweeteners and flavourings into your gut.

A zero on the label is not always zero. US rules let a serving with under 5 kcal be labelled calorie free. Two servings across a morning still come to under 10 kcal, far below the common 50-calorie rule of thumb, which is not an official limit.

The drink around the syrup matters more than the syrup. A sugar-free vanilla latte is still a milk drink, and 200 ml of 2% milk adds about 100 kcal. That breaks a fast for every goal. If you fast for weight loss, a pump of sugar-free syrup in black coffee is a small trade-off. For a strict autophagy or blood-sugar fast, drink the coffee plain.