Fasting is the practice of going without food — voluntarily abstaining from eating for a period. The motives span the sacred and the practical: Ramadan, Lent, and Yom Kippur make fasting a religious discipline; political hunger strikes make it protest; and modern health culture makes it a weight-loss and “wellness” strategy in forms from intermittent fasting to prolonged water fasts. Physiologically, the body moves through its reserves in order — glycogen first, then fat with ketone production, then, in prolonged starvation, protein — which is why short fasts are tolerable and long ones dangerous. Medicine uses fasting too: pre-surgical fasting prevents aspiration, and diagnostic fasts test metabolism. The practice is ancient and universal; the current fashion for it is new, and the evidence for its health claims remains mixed.