The term metabolism in its broad sense may be defined as the sum of all the chemical changes which occur in the living organism.  Defined in this way, it includes practically all of physiology and biochemistry, and much of the present volume could be included under this heading. In a more limited sense, how ever, the term is used to designate the processes whereby the foodstuffs taken into the organism are utilized to form the constituents of the body, to yield the heat necessary for maintaining a constant body temperature, and to furnish the energy necessary for maintaining the cellular and other manifold activities which characterize the living organism. Read more

When foodstuffs are ingested by a fasting individual in the resting state they are incorporated into the body pool and thus serve to replace the body tissues otherwise consumed doing starvation. However, such ingestion involves an accelerated rate of metabolism which is designated as the specific dynamic action of food. This amounts to approximately 30, 6, and 4 percent above the basal level for protein, fat, and carbohydrate, respectively. Thus an individual whose basal caloric requirement was 2000 kcal daily would have to be supplied with an amount of protein equivalent in caloric content Read more