<unk>  is a biological process in which the body breaks down fat and muscle tissue in order to stay alive.<unk>  occurs only when there is no longer any source of protein, carbohydrate, or vitamin nourishment feeding all body systems; it is the most severe type of malnutrition.
Catabolysis
Metabolism
Excretion
Redox
Reuptake
Drug metabolism
Ethanol metabolism
Drug recycling