Effects of Amino Acid Supplements on the Nutritive Value of Maize Protein for Human Adults

Abstract

The effect of supplementing the protein of whole maize meal was studied by prolonged nitrogen balance studies on eight metabolically normal men accustomed to eating large amounts of maize. In each experiment the subject served as his own control while different combinations of amino acids were given to replace a small part of the maize protein. It was found possible to measure the effects of these supplements under the natural conditions of a protein intake near 1 gm./kg. body weight (9 per cent dietary calories from protein) and under static conditions. The small positive nitrogen balance obtained with the subjects receiving unsupplemented maize under these conditions is considered to have been apparent and not real, because nitrogen losses via the skin were not measured. The data indicate that the chief limiting amino acids in the maize that was tested were lysine, tryptophan and isoleucine in that order of importance. However, lysine had little effect when extra vitamins were not given and other varieties of maize contain less tryptophan. A practical supplement of maize protein should therefore provide both tryptophan and lysine. Further benefit is to be expected from the inclusion of isoleucine.