THE CHEMICAL COMPOSITION OF THE ADULT HUMAN BODY AND ITS BEARING ON THE BIOCHEMISTRY OF GROWTH

Abstract

The amounts of nutrients contained in the adult human body represent the integration of the day to day accretions from the time of conception to the termination of growth. These accretions are usually determined by balance experiments carried out at different periods of growth and are assumed to measure the net requirements of the respective nutrients with due consideration of the synthesis and transformation of organic nutrients in metabolism. Thus, the accretion of fat does not measure a fat requirement, but the accretion of protein and of the essential mineral elements may. Whether it does, or whether it does not, ivill depend upon the capacity of the body to store the nutrient in amounts considerably greater than current needs. The capacity of the body t,o store protein is strictly limited; so that nitrogen balances secured on a growing child after a reasonable period of adjustment to a liberal int’ake will measure reasonably well the amount needed for maximum growth in terms of net protein. The capacity of the body t,o store calcium is relatively enormous, far in excess of the needs of the soft tissues of the body and quite probably in excess of the need for a rigid and strong skeletal structure. Calcium balances on the child subsisting upon a liberal calcium intake may or may not measure the day to day need for net calcium, depending upon the degree of saturation of the skeleton in calcium salts,.a condition that may vary with metabolic factors as well as with the food supply. The extent to which metabolic balances of nitrogen, calcium, iron, etc., actually measure the day to day requirements in terms of net nutrients’ can be judged by comparing their total integration throughout growth with the composition of the mature body with respect to them. However, information on the composition of the adult human body is strangely contradictory and incomplete. The situation may be illust,rated by the information on the content