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Determination of the Minimum Dietary Essential Amino Acid-to-Total Nitrogen Ratio for Beef Protein Fed to Young Men^1,2,

Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts

The extent to which beef protein could be isonitrogenously replaced with nonspecific nitrogen without influencing the efficiency of dietary nitrogen utilization was studied in 9 male college students. They were fed at constant nitrogen intakes, equivalent to 0.39 g protein/kg body weight, and daily urinary nitrogen was measured. Strained beef protein furnished 90% of the nitrogen of the basal diet, with oatmeal and tomato juice the remainder. When the nitrogen of the basal diet was isonitrogenously replaced by a nonspecific nitrogen source, a mixture of glycine and diammonium citrate in which each furnished equal amounts of nitrogen, a 20% replacement caused a barely significant increase in urinary nitrogen excretion in one of the five healthy subjects studied. A 25% replacement caused no significant increase in urinary nitrogen excretion in three of four healthy subjects studied, but a 30% replacement was tolerated by only two of six subjects. A 20% replacement gives an E/T_N ratio of 2.16 and 26.4% of the total nitrogen furnished by essential amino acids; 25% replacement results in an E/T_N ratio of 1.89 and 24.3% of the nitrogen from essential amino acids. Sulfur-amino acids and tryptophan may be limiting in the 30% diluted diet. One subject receiving a 20% dilution showed a markedly increased nitrogen excretion during an acute febrile infection despite the low protein intake.

² This investigation was supported in part by grants from the National Live Stock and Meat Board, and by Public Health Service Research grant no. AM 06274 from the National Institute of Arthritis and Metabolic Diseases.

³ On leave from the Department of Biochemistry, National Taiwan University College of Medicine, Taiwan, supported by NIH Fellowship no. I FO5-TW-853-01.

Manuscript received 26 May 1966.