Lysine and Tryptophan Content of Proteins and Their Utilization for Human Growth

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Abstract
Data have been presented which support the conclusion that the carcass analysis procedure proposed by Mitchell may be a valid method for evaluating the human growth needs for some "essential" amino acids. In particular, the available evidence indicates that the utilization of dietary proteins increases as their lysine and tryptophan content approaches that of muscle tissues. This concept gains further validity from the fact that the nutritional value of some protein products with low lysine/tryptophan values can be enhanced by small additions of lysine. In milk protein products this increased utilization approached that of bovine muscle and plasma digests and appears to be a linear function of the augmented lysine/tryptophan values. Lysine supplementation of wheat gluten increased its nutritive value to that of milk proteins. The practical implications of these findings in the protein nutrition of infants of population groups of low economic status are discussed. Reference is made to the possible role of amino acid deficiencies in malignant malnutrition (kwashiorkor) of infants maintained on restricted or poorly supplemented breast feeding.