Intermittent fasting (IF) is an eating pattern — not a diet — that cycles between defined periods of fasting and eating. The most popular protocol is 16:8: 16 hours of fasting followed by an 8-hour eating window. During the fasting period, the body shifts from glucose-burning to fat-burning metabolism, and autophagy (cellular cleanup) may increase.
Wilkinson et al. (2020, Cell Metabolism) ran a 12-week single-arm study of 10-hour time-restricted eating (a 14:10 schedule) in adults with metabolic syndrome and reported lower weight, blood pressure and atherogenic lipids. De Cabo & Mattson (2019, New England Journal of Medicine, 381, 2541–2551) reviewed the mechanistic evidence and found that the metabolic switch from glucose to ketone bodies during fasting activates cellular stress response pathways, promotes mitochondrial biogenesis, and triggers autophagy — the cellular "self-cleaning" process that declines with age. Animal studies link fasting to increased autophagy (Alirezaei et al., 2010, Autophagy, in mice), but the timing in humans is not established.
After an extended fast, reintroduce food gently. Start with easily digestible foods — fruits, vegetables, light protein. Avoid large carbohydrate-heavy meals immediately, which can cause a sharp insulin spike after a period of insulin sensitivity. Hydrate well, as fasting periods naturally reduce water intake from food.
Intermittent fasting is not suitable for everyone. Avoid IF if you are pregnant or breastfeeding, have a history of eating disorders, are underweight, or have diabetes (without medical supervision). Always consult a doctor before starting any fasting protocol if you have a chronic health condition or take medication.