Clean Fasting

Clean fasting is the practice of consuming nothing but water and other strictly calorie-free drinks that do not trigger a metabolic response during the fasting window. On a clean fast, only water, black coffee, plain tea, electrolytes, and certain non-caloric supplements are considered acceptable, because none of them provides calories or provokes a meaningful metabolic response.

The purpose of clean fasting is to fully reach the strictest fasting goals. Benefits like autophagy, the body's process for repairing and recycling cell components, depend on calories and insulin staying as low as possible, and they are the most easily interrupted. For that reason, clean fasting excludes anything with calories or anything that raises insulin or stimulates digestion, such as cream, bone broth, and protein or BCAA supplements.

Clean fasting is one end of a spectrum, with dirty fasting at the other, where small amounts of calories are allowed in exchange for easier adherence. Neither is inherently correct, and the right choice depends on what the fast is meant to achieve and on what a person can sustain. Clean fasting is simply the stricter interpretation, chosen when the priority is keeping the fasting window fully intact.