The famine response is the body’s metabolic answer to starvation — the same state biochemists call ketosis. When food runs out, the body burns through its glycogen within a day, then shifts to fat: the liver converts fatty acids into ketone bodies, which fuel the brain and spare protein, slowing the cannibalisation of muscle. Metabolic rate drops, non-essential functions shut down, and the body becomes ruthlessly economical — the physiology that lets humans survive weeks without food. The response is adaptive brilliance and terrible cost: it preserves life while wasting the body. Modern weight-loss diets borrow the mechanism deliberately, inducing mild ketosis with very-low-carbohydrate eating. But the famine response evolved for famine — a survival mode, not a lifestyle — and its prolonged activation carries the risks of the starvation it was built to endure.