The Effect of Dietary Protein and Calorie Restriction on Growth, Kidney Function, and Survival of Male Rats

(From the Introduction): One of the primary goals of nutrition research is to determine the levels of various nutrients which are needed to promote rapid mental and physical growth, optimal physiological performance during maturity, and the retention of good health during old age (1). It is generally considered that the intake of nutrients at levels moderately above those required for maximum rates of growth and development are optimum for the well-being of an organism. However, it has been shown that life span can be increased and the age-associated decline in physiological function delayed in experimental animals fed diets containing lower levels of nutrients than those required for optimal growth and development.

There is much controversy as to the relative effect of decreased caloric and protein intake on life span of experimental animals (2). It is generally accepted that the reduction of feed intake increases longevity. However, the results of studies which investigated the effect of dietary protein on life span are equivocal and the level of caloric intake was not comparable between dietary protein levels. In addition, the reduction of caloric intake in most studies was accompanied by a decrease in protein intake.

Restriction of calories and/or protein has been reported to decrease the incidence of renal lesions in old rats and delay the age-associated decline in renal function (3). While a reduction in urinary protein excretion and an improvement in the transport of para-amonohippuric acid has been demonstrated in calorically restricted animals, the effect of dietary protein intake on these biochemical parameters has not yet been determined.

It was the purpose of this study to investigate the effects of protein restriction with and without caloric restriction on growth and survival of rats and to determine the effects of these diets on renal function. In addition, the effect of gradually changing the level of dietary protein during growth and development without reducing caloric intake on these parameters was studied.

It was hypothesized that caloric restriction would reduce rates of growth and mature body weights and produce physiologically younger animals as indicated by improved renal function and increased survival. It was further hypothesized that protein restriction with or without caloric restriction would reduce rates of growth but not mature body weights and produce physiologically younger animals.