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 to 2600 kcal in order to prevent weight loss. In the case of carbohydrate, only 2120 kcal would be required, and in the case of fat, only 2080 kcal.

The additional caloric requirement due to the specific dynamic action is only in small part utilized in the processes of digestion and represents an actual stimulation of oxidative processes in the tissues, the exact nature of which is not established. The high specific dynamic action of protein is in part the basis for the recommendation of a high protein in take in reducing diets. However, of greater significance is the relative satiety value of calorically equivalent amounts of the three nutrients which is determined by their relative bulk, the rate of their assimilation, and their effect on the glucose level of the blood. Protein and fat maintain a prolonged blood – sugar level, while carbohydrate results in a hypoglycemic after reaction which tends to stimulate hunger.

This, rather than body size, reflects the active protoplasmic mass of the organism. In starvation, inanition, hypothyroidism, hyperphysical or adrenal cortical insufficiency, and nephritis the metabolic activity is reduced; while in fever, hyperthyroidism, leukemia and other malignancies, polycythemia, congestive heart failure with dispend, and diabetes insipid us it is increased.