Urinary and Fecal Excretion of Endogenous Nitrogen by Infants and Children

Abstract

Urinary and fecal excretions of endogenous nitrogen were determined in metabolic balance studies with normal 4- to 6-month-old North American infants and well nourished but dwarfed 3- to 8-year-old African children. Data from these studies and from several studies of North American adults are analyzed. The importance of controlling prior intake of protein is stressed. When prior intake of protein had been “low or intermediate,” mean urinary excretion of nitrogen by infants, children and adults was 37, 48 and 30 mg/kg/day, respectively, during the fourth through sixth days of ingesting the protein-deficient diet. Corresponding fecal excretions of nitrogen were 20, 25 and 11 mg/kg/day. When urinary excretion of endogenous nitrogen is expressed in relation to basal caloric consumption, the mean value for 4- to 6-month-old infants is only about one-half the mean value for adults (0.6 versus 1.2 mg/basal kcal). The data therefore do not offer support for the concept that urinary excretion of endogenous nitrogen is related in a fundamental physiologic manner to basal metabolic rate.