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The addition of increasing amounts of lysine to a diet of dried bread supplemented with fat, salts, and vitamins brought about significant growth responses in weanling rats. For example, a supplement of 0.5% dl -lysine·HCl, corresponding to 0.2% l -lysine, to a bread diet improved the average gain in weight after 5 weeks from 32% to about 75% of the average gain on the stock diet. An equal response is obtained from lysine added to flour before baking or from lysine added in corresponding amounts to the bread diet. At the end of 6 months the diet containing the supplement of 0.2% lysine had produced rats that were practically equal in weight to those receiving diets with larger additions of lysine. The animals on the basal bread diet did not attain weights comparable with those receiving the lysine supplements. If sufficient lysine was added to bring the total l -lysine content of the diet to about 0.8%, or more, a growth response similar to that obtained with the stock diet was observed. These results suggest that, so far as rat growth is concerned, the only important amino acid deficiency in commercial bread is lysine.

The nutritional effect which may be obtained by the addition of lysine, methionine, valine and threonine to a diet composed of commercial white bread, fat, salts, and vitamins has been investigated with weanling rats. A beneficial effect could be observed only from the addition of lysine. The results of these experiments indicate that, as far as rat growth is concerned, the only amino acid deficiency in commercial white bread is lysine.

SummaryResults with lysine-supplemented experimental diets and with stock diet show that the lipid content of the tibia is relatively low when sufficient lysine for optimum growth is available to young rats. With the lysine-deficient diet, growth is retarded and bone lipids are increased. Interference with production of normal bone marrow appears to be a definite indication of lysine deficiency.