Does decaf coffee break a fast?

A 240 ml (8 fl oz) cup of black decaf coffee brewed in water has 0 to 2 kcal, no sugar and almost no protein. USDA data list under 1 kcal per 100 ml, a little less than regular black coffee at about 2 kcal a cup. The common 50-calorie rule of thumb is not an official limit, and decaf sits far below it.

This site sorts answers by four goals, and decaf gets the same verdicts as regular black coffee. It is safe for weight loss and blood sugar because it has almost no calories and no sugar. It is safe for autophagy too. In mice, regular and decaf coffee both increased autophagy within 1 to 4 hours, but no human study has tested it either way. Gut rest is a grey area. Coffee stimulates stomach acid and gets the bowel moving, so the database does not count it as rest for your gut.

Decaf still contains some caffeine. An 8 fl oz (240 ml) cup usually has about 2 to 15 mg, against about 95 mg in a cup of regular brewed coffee. Caffeine from a regular cup can still cut into sleep if you drink it within about 9 hours of bed. Decaf lets you keep a hot drink in the evening part of a fast without that cost.

What you add to the cup changes the answer. A tablespoon of sugar-free creamer adds about 15 to 20 kcal, mostly from fat. A splash of milk (2 tbsp) adds about 12 to 18 kcal. Either one breaks a fast for autophagy and gut rest. If you are pregnant or breastfeeding, the caffeine limit is 200 mg a day, and black decaf adds very little towards it. Talk to a doctor before you fast if you are pregnant.