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Effect of Protein Nutrition on Growth and Life Span in the Rat

Department of Nutrition and Biochemistry, Institute of Public Health, Tokyo, Japan

The effect of the amount and composition of protein (10, 18, and 27% casein and pure amino acid mixture diet) on growth and life span of rats was examined by using littermate females. Tail length and body weight were measured, and estrus cycle was examined by a smear test. In addition, body constituents were determined several times during the growing period. Tail length and body weight on the rats fed 10% casein diet were less than those of rats fed 18% or 27% casein, or an amino acid mixture early in the growth period. However, the difference seen among them became insignificant later in the growth period, except in the case of 27% casein-fed rats. It was found that both the amount of protein intake and variance of littermates, which refer to litters of different mothers, had statistically significant effect on growth, especially in the earlier part of growth. Estrus cycle appeared later in the 10% casein-fed rats and seemed to be irregular longer, as compared with that of rats in other groups. With respect to body constituents, concentration of water was higher and that of fat was lower soon after weaning, and then the relative water content decreased and the fat increased during the growth period, irrespective of the difference in diet. From the results obtained in the present experiments, it was concluded that the effect of difference in diet, containing 10 or 18% casein, or an amino acid mixture corresponding to 18% casein, on life span was not significant. The variance of littermates was relatively great but, in the case of 27% casein diet, both the difference in diet and the variance of littermates had no statistically significant effect on life span. The present experiment indicates that an amino acid diet, when properly composed, will support growth and life span closely approaching that obtained with casein.