Fasting basics
What breaks a fast?
A practical guide to calories, sweeteners, coffee, electrolytes, and modified fasting.
5 min
The simple rule
For a clean fast, stay with zero-calorie drinks: water, black coffee, unsweetened tea, and zero-sugar electrolytes. Anything with calories belongs in the eating window.
The real-world rule
Many people still get results with small amounts of lemon, diet drinks, or gum. Track how they affect hunger, cravings, and consistency.
When to be stricter
If you are fasting for glucose control, appetite training, or medical reasons, keep the fasting window cleaner and ask your clinician for personal guidance.