Studies on Protein Requirements of Young Men Fed Egg Protein and Rice Protein with Excess and Maintenance Energy Intakes

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Abstract
Following a period of eating a standard diet, young men were given diets containing low levels of egg or rice protein varying stepwise from 0.28 to 0.76 g/kg for 3 weeks. To determine the effect of excess energy intake with a low protein diet, the subjects were divided into two groups: one group received the same level of energy as with the standard diet (ca. 45 ± 2 kcal/kg), while the other was given a daily surplus of about 700 to 1,000 kcal (ca. 57 ± 2 kcal/kg). Protein requirements were estimated by regression analysis of balances at different levels of intake. Results showed that: 1) Administration of excess energy spared loss of labile protein and reduced the time required for adaptation to a low protein diet, with establishment of a nitrogen balance at a lower level than with a maintenance energy diet. 2) Supply of excess energy resulted in increased availability of ingested protein, with a reduction of the protein requirement: with maintenance energy the practical requirements were estimated as 0.65 g/kg with 44 NPU for egg protein and 0.87 g/kg with 33 NPU for rice protein, whereas with excess energy the minimum requirements were 0.46 g/kg with 63 NPU and 0.58 g/kg with 50 NPU, respectively. The possibility that the biological value of dietary protein may be variable rather than constant was discussed.