Does diet soda break a fast?

A 355 ml (12 fl oz) can of diet cola sweetened with aspartame has about 7 kcal and about 1 g of carbohydrate. A saccharin-sweetened can has 0 kcal. Labels often say zero, because US rules let a serving under 5 kcal show as 0. Regular cola is a different drink, with about 155 kcal and 37 g of sugar a can.

This site rates items against four goals of its own design. Diet soda is grey for all four, weight loss included, because it tastes sweet. Whether sweeteners raise insulin is unresolved, and the answer may vary between people. In a 2022 trial, sucralose and saccharin worsened blood-sugar responses in some people, linked to their gut bacteria. WHO advises against non-sugar sweeteners for weight control, as a conditional recommendation.

A caffeinated diet cola has about 43 mg of caffeine a can. Count it toward the 400 mg a day that healthy adults can have, or 200 mg in pregnancy. Aspartame contains phenylalanine, and US labels carry a warning for people with phenylketonuria (PKU).