This is a summary of the physiological responses to the total or near-total absence of nutrition. In brief, the metabolic response to starvation is characterised by a switch from carbohydrate metabolism to fat metabolism, in the context of a hypometabolic state, with minimised catabolism. Initially, stores of carbohydrate precursors (eg. glycogen) are depleted. Then, in the first 24-48 hours there is increased gluconeogenesis from amino acids and glycerol. Subsequently, ketogenesis takes over, and much of the body metabolic needs are met by ketone bodies and free fatty acids. This is the consequence of decreasing insulin levels, and relatively increased influence from catecholamines and cortisol. Over prolonged starvation, protein catabolism begins, resulting in degradation of structurally important proteins, and organ system dysfunction.