Partial Dietary Replacement of Milk Protein by Nonspecific Nitrogen in Young Men

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Abstract
Skim milk protein was replaced isonitrogenously by glycine and diammonium citrate, or by a mixture of nonessential amino acids in the test diet of 21 male college students; the effect of this replacement on urinary nitrogen and sulfur excretion and on fasting plasma amino acid concentration was studied. The subjects were fed a constant nitrogen intake equivalent to 0.38 g protein/kg body weight. Skim milk protein furnished 90% of the daily protein; oatmeal furnished the remainder. In experiments 1 and 2, glycine and diammonium citrate replaced 20 and 25% of total dietary nitrogen, respectively. In experiment 3, a mixture of nonessential amino acids replaced 25% of dietary nitrogen. The 20% replacement with glycine and diammonium citrate did not increase urinary nitrogen excretion in any of the seven subjects, but three of the seven showed lower urinary nitrogen excretion after return to the basal diet. A 25% replacement with glycine and diammonium citrate increased urinary nitrogen excretion in three of seven subjects and four subjects showed lower nitrogen output during the final basal period. The 25% replacement with nonessential amino acids did not change urinary nitrogen excretion but 3 of 10 subjects showed a variable decrease in nitrogen excretion during the second basal period. As a replacement for 25% of total dietary protein, nonessential amino acids appeared a more effective nonspecific nitrogen source than glycine and diammonium citrate. Fasting plasma amino acids levels were unchanged during the experimental periods.