Length of Life and Nutrition in the Rat

The effect of uniform lifelong dietary regimens on the mortality patterns of rats has been investigated. More than 1000 male rats divided into 8 groups received one of 4 experimental diets per group which were allotted on a restricted as well as on an unrestricted basis. The various dietary regimens were begun at weaning age. The influence upon mortality patterns of precise intakes of protein (casein) and of carbohydrate (sucrose) and of variation in the ratios between these two components in an otherwise “adequate” diet, has been assessed. Actuarial tables have been constructed for each of the populations and include determination of mortality distribution, mortality rates, survival pattern and life expectancy at successive ages. Mortality ratios and life expectancy indexes of the populations consuming semisynthetic diets have been computed. The effects obtained by restriction of intake of the experimental diets were, in general, more beneficial for all length-of-life parameters measured than when the diets were administered on an unrestricted basis. Restricting the intake of the protein component only, in two diets allotted on an isocaloric basis had little effect. Restricting the intake of carbohydrate only with simultaneous restriction of caloric intake enhanced life expectancy. Restricting the intake of both protein and carbohydrate with simultaneous restriction of caloric intake, though showing no pronounced effects early in life, enhanced life expectancy to the greatest degree because of the beneficial effects later in life. When these same diets were fed on an unrestricted basis there were greater differences in mortality patterns between each population than were found when feeding was restricted. Under unrestricted conditions a relationship between length of life and intake of protein, carbohydrate, and the proportion of these components of the diet, was found for only one group. Rats in this group which received a diet low in protein and high in carbohydrate restricted their own intake and therefore their total intake of calories and had the longest life span. Length of life has been found to be influenced not only by quantitative dietary restrictions but also by the ratio of the protein and carbohydrate components in the diets.