Dirty Fasting

Dirty fasting is the practice of allowing small amounts of calories during the fasting window, on the view that staying close to a fasted state captures much of the benefit. A dirty fast might include a splash of cream in coffee, a small serving of bone broth, MCT oil, or BCAAs, none of which fit a strict definition of fasting but each of which is kept small.

The logic behind dirty fasting is that a strict fast is harder to sustain, and a small intake of calories can make a long fasting window more comfortable to keep to. The goal is to hold on to the benefits that do not require a perfectly strict fast, such as appetite control, fat-burning, and staying in a low-insulin, fat-adapted state, while accepting that the deepest effects, particularly autophagy, are reduced or lost. In short, dirty fasting trades the strictest goals for the ability to keep fasting consistently.

Dirty fasting sits at the opposite end of the spectrum from clean fasting, which permits only water, black coffee, plain tea, electrolytes, and certain non-caloric supplements. Which approach fits depends on the goal: a fast aimed at appetite control or simple calorie reduction tolerates a dirty approach well, while a fast aimed at autophagy calls for a clean one. Dirty fasting is best understood as a deliberate compromise between strictness and sustainability.