Protein Requirements of Man: Efficiency of Egg Protein Utilization at Maintenance and Sub-maintenance Levels in Young Men

Abstract

The purpose of these studies was to evaluate the assumptions made in estimating minimum protein requirements by the factorial method. A series of nitrogen (N) balance experiments were conducted with young male M.I.T. students given egg protein at or below their maintenance requirements. Data from previous studies are also included, involving a total of 107 subjects with 131 separate balance periods. In a few subjects, measurements were also made of urinary urea and creatinine and of various serum constituents, including acidic and neutral free amino acid levels, in blood samples drawn after an overnight fast and 3.5 to 4 hours after breakfast. The significance of the amino acid changes with alterations in egg protein intake is discussed in relation to the requirements for essential amino acids. The efficiency of egg protein utilization was not constant throughout the submaintenance range of protein intake; the overall N balance data showed a curvilinear decrease as protein intake approached maintenance levels. By regression analysis, the mean requirement for egg protein N in young men was estimated to be 73 mg N/kilogram body weight/day, the 95% confidence interval falling between 60 and 94 mg N/kilogram body weight. These results also indicate that the evaluation of dietary protein quality in adult man should be carried out at more than one level of protein intake.