Studies on Amino Acid Excretion in Man. Iii. Amino Acid Levels in Plasma and Urine of Normal Men Fed Diets of Varying Protein Content 1

Current emphasis on the use of proteins in the treatment of various disorders of the alimentary tract has stimulated a comparative study of certain aspects of protein metabolism in normal persons and in patients with gastro-intestinal disease. In addition to the usual nitrogen balances, microbiological assays were made of eight amino acids in food, acid-hydrolyzed whole plasma, tungstic acid filtrates of plasma (free amino acids), acid-hydrolyzed tungstic acid filtrates of plasma (free plus combined amino acids),' hydrolyzed urine, and in feces. The amino acids measured were methi- onine, lysine, arginine, histidine, leucine, isoleu- cine, valine and threonine. The present paper deals with individual amino acid levels in the food, plasma, and urine of two normal adult men fed isocaloric diets of differing protein content.