The dependence of tumor formation on the composition of the calorie-restricted diet as well as on the degree of restriction. 1945.

The inhibitory effect of caloric restriction on the formation of tumors in the mouse has been shown (1 I) to be dependent on the actual degree of caloric restriction. Previously it had been demonstrated (8) that restriction of caloric intake to about 60 per cent of the ad libitum intake causes an inhibition in tumor formation regardless of whether only the carbohydrate component is restricted (so-called caloric restriction per se) or an aliquot of the ad libitum ration is fed (restriction of all components). The question arose whether these two types of restricted diets affect tumor formation to the same extent. Also, since it is known that a fat-enriched diet enhances the formation of spontaneous mammary and induced skin tumors (1, 9) it was of interest to determine the effect of high-fat but restricted diets on tumor formation. The present experiments, in which spontaneous mammary and induced skin tumors of the mouse were utilized, were performed in order to gather more data regarding the effect on tumor formation of the degree of caloric restriction, and at the same time to ascertain whether or not there is a differential effect due to the composition of the diet (at various caloric levels). Three types of restricted diets were used: (a) diets in which caloric restriction was achieved by decreasing the carbohydrate component only; (b) diets in which caloric restriction was achieved by reducing all components of the control ration (not necessarily in proportion to the caloric restriction); and (c) diets equivalent to the latter except that the fat content was increased by equicaloric substitution of fat for carbohydrate.