ADAPTATION OF URINARY NITROGEN EXCRETION IN INFANTS TO CHANGES IN PROTEIN INTAKE

1. Thirty-six nitrogen-balance measurements were made on children recovering from malnutrition. Two types of diet were used: a high-protein diet providing from 1.25 to 6.0 g protein/kg per day which supported normal growth, and a low-protein diet providing 0.75 g protein/kg per day on which the children were approximately in N balance. Both diets provided 120 kcal/kg per day. 2. The size of the labile protein pool was estimated from the N lost on changing from a high- to a low-protein diet. After the change of diet a new equilibrium was reached in about 3 days. 3. Labile protein, as defined above, represented about 1.2% of the total body protein on changing from 6.0 to 0.75 g protein/kg per day, and about 0.2% of total body protein on changing from 1.5 to 0.75 g protein/kg per day. The magnitude of the labile protein pool did not appear to be related to the nutritional state of the child. 4. It is concluded that the labile protein pool is not a reservoir which can be filled, but that losses of N which occur on reducing the protein intake of an infant reflect a lag in metabolic adjustment. © 1968, The Nutrition Society. All rights reserved.