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

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Abstract
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/TN ratio of 2.16 and 26.4% of the total nitrogen furnished by essential amino acids; 25% replacement results in an E/TN 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.