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Human Protein Requirements: A Long-Term Metabolic Nitrogen Balance Study in Young Men to Evaluate the 1973 FAO/WHO Safe Level of Egg Protein Intake^1,2,

Department of Nutrition and Food Science, and Clinical Research Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Six Caucasion male MIT students, age 19 to 23 years, were given a formula diet providing 0.59 g egg protein/kg body weight/day and energy intakes approximately 10% above their usual requirements. Four subjects continued on this diet for 81 to 89 days, but for two the protein intake was increased after 50 and 59 days because of an excessive rise in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels. The elevated serum AST and ALT activities fell to normal rapidly when these subjects received a diet providing 1.5 g protein/kg/day from skim milk powder. Body weight increased in five of the subjects. Four showed cumulative negative N balances, and all showed a net loss of total body ⁴⁰K, which was significant in three. These findings indicate that the 1973 FAO/WHO "safe level" of egg protein intake of 0.57 g/kg is not sufficient for long-term maintenance of most healthy young men. Moreover, the greater N losses calculated from ⁴⁰K and creatinine measurements than from the N balance data suggest an integumental N loss approximating 15 mg/kg rather than the 5 mg of the 1973 allowances.

KEY WORDS: • human protein requirements • 1973 FAO/WHO protein allowance • N balance • serum transferase

¹ Supported, in part, by NIH Grant AM 15856, The MIT Health Sciences Fund, The Lord Rank Research Centre, High Wycombe, England, and Grant RR-88 from the General Clinical Research Centers Program of the Division of Research Resources, National Institutes of Health. Dr. Garza was supported by NIH Training Grant 5-TO1-AMO 5371-13.

² Contribution No. 2766 from the Department of Nutrition and Food Science, Massachusetts Institute of Technology.

Manuscript received 5 January 1976.

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