Lysine in Human Nutrition

Abstract

The roles of lysine, in particular, and protein, in general in nutrition, have been discussed. The lysine requirements for both growing and adult man and the rat have been presented as milligrams per kilogram per day, in terms of the lysine/tryptophan ratio, as grams of lysine/16 gm of nitrogen, and as percentage of diet. It has been suggested that requirements should be discussed in relation to protein and calorie intakes, not just as milligrams per kilogram of body weight per day. The concept of balance in protein nutrition has been discussed, and studies of lysine supplementation in both man and animals have been evaluated. Signs of lysine deficiency have been reviewed. Studies on lysine toxicity in man and animals, and amino acid imbalance as it is related to lysine have been discussed, and it is concluded that neither toxicity nor imbalance poses a significant hazard in the proper use of lysine as a dietary supplement. Effects of lysine on calcium absorption, dental caries, gastric secretion, anemia, and in potassium deficiency have been reviewed in the light of known and possible physiological and physical properties of lysine. Optimal vs. minimal nutrition, including limitations of the nitrogen balance method and the concept of protein reserves, have been discussed, and the evidence for protein malnutrition in this country has been reviewed. It is concluded that the great majority of people in the United States consume diets more than adequate in protein both in quality and quantity. The evidence clearly indicates, however, that there are population groups in all sections of the country — particularly among adolescents, pregnant women, older people and people in poor economic groups — in which the National Research Council's recommended daily allowance for protein is not met. Bread, flour, and other cereal foods tend to be more important sources of protein for such groups than for the population as a whole. It is concluded that foods, diets, and individual meals that are limiting in lysine can be improved by lysine supplementation. People who derive a good part of their protein intake from animal sources are not likely to respond to lysine supplementation. Those population groups in this or any other country which derive a substantial part of their protein intake from cereals, particularly wheat, will probably benefit from supplemental lysine. In terms of individual foods, the evidence is conclusive that the protein in bread, macaroni products, and other wheat foods can be substantially improved by supplementation with lysine. More clinical evidence is needed, however, to establish whether lysine supplementation will in fact improve the nutritional status of any important number of individuals in this country, as is theoretically possible. It is to be hoped that such clinical studies will be carried out to investigate further the potential value of lysine supplementation in improving the nutritional status of population groups in this and other countries.