The relationship between dietary intake, weight change, nitrogen balance, and protein turnover in man.

We have examined the relationships between protein turnover, protein synthesis, and protein breakdown and dietary intake, weight change, and nitrogen balance in children who were recovering and had recovered from severe protein-energy-malnutrition. Protein metabolism was measured by giving [15N]glycine and measuring the enrichment of urinary urea. The level of dietary protein did not affect protein metabolism. There were highly significant correlations between both protein flux and protein synthesis and the ad libitum dietary intake, nitrogen balance, and weight change. Over the range of dietary intake, 60 to 270 cal/kg per day, the protein synthesis rate increased 5-fold. Large changes in dietary intake resulted in small changes in protein breakdown, with breakdown being least on an inadequate intake. Changes in the rate of protein breakdown did not contribute to changes in nitrogen balance or body weight.