fat metabolism, the biochemical process by which fats are broken down, incorporated, and used by the cells of the body. Fats provide more food energy (9 kcal/g) than carbohydrates (4.1 kcal/g). Fat catabolism begins with the hydrolysis of fats (triglycerides) into glycerol and fatty acids. Glycerol is converted into a compound that can enter the citric acid cycle. Catabolism of fatty acids continues by beta-oxidation to produce acetylcoenzyme A, which also enters the citric acid cycle. The body synthesizes fats from fatty acids and glycerol or from compounds derived from excess glucose or from amino acids. The body can synthesize only saturated fatty acids; essential unsaturated fatty acids can be supplied only by diet. Fat metabolism is controlled by hormones such as insulin, growth hormone, adrenocorticotropic hormone, and glucocorticoids. The rate of fat catabolism is inversely related to the rate of carbohydrate catabolism, and in some conditions, such as diabetes mellitus, the secretion of these hormones increases to counter a decrease in carbohydrate catabolism.
