Protein-energy requirements of prepubertal school-age boys determined by using the nitrogen-balance response to a mixed-protein diet

Short-term nitrogen-balance response to a vegetable-protein mixed diet and to a milk-egg protein diet was tested in eight healthy male children 8–10 y old. They received 96, 128, 160, and 192 mg N·kg body wt−1.d−1for 10 d while on the mixed diet and 160 mg N·kg−1·d−1on the milk-egg diet. The mean regression equation was nitrogen balance = 0.52 (nitrogen intake) -68.3, all in mg N·kg−1·d−1. Apparent nitrogen digestibility was 82% and 86% for the mixed and milk-egg diets, respectively, when the subjects received 160 mg N·kg−1·d−1. Mean nitrogen intake for satisfactory nitrogen retention on the mixed diet was 150 mg N·kg−1·d−1; the suggested protein recommended allowance to cover 97.5% of the population was derived by using a CV of 12.5% is 1.2 g protein.kg−1·d−1. We conclude that present recommendations are adequate for short-term nitrogen retention; long-term studies are needed to evaluate the chronic safety of this protein allowance.