Lysine and Methionine Supplementation of All-Vegetable Diets for Human Adults

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Abstract
Nitrogen intake and excretion data for young adult subjects consuming all-vegetable diets with and without supplements of lysine and methionine are presented. The essential amino acids of the diet were determined. An all-vegetable diet supplying 25 gm of protein per day of which 48% of the protein came from wheat products and 62% from cereals, contained all of the essential amino acids in quantities equaling or exceeding Rose's estimated minimum requirements. The amount of methionine plus cystine barely equaled the estimated requirement. Supplementation of the diet with lysine improved the nitrogen retention following a depletion period and methionine plus lysine supplements appeared to improve the retention still more. These data are interpreted as demonstrating improvements in biological value of the dietary protein. Considering the relative ease with which the subjects approach nitrogen equilibrium on the unsupplemented diet, the likelihood of protein or amino acid deficiencies in an adult population consuming diets essentially of vegetable origin does not appear to be very great. The data emphasize the probability that the proteins of fruits and vegetables which are usually not considered to be of importance in protein nutrition may be an important supplement to the cereal proteins.