The Dependence of Tumor Formation on the Degree of Caloric Restriction

Abstract

In previous publications (4, 5) it has been reported that caloric restriction of the diet causes an inhibition of tumor formation in the mouse. This effect occurred whether the restriction was obtained by decreasing only the carbohydrate component of the diet (so-called caloric restriction per se) or by feeding smaller amounts of the ad libitum ration (all components restricted proportionately). In our laboratory, the inhibitory effect of caloric restriction has been demonstrated for spontaneous mammary and lung tumors and for induced epithelioma and sarcoma. Since caloric restriction affected these four different types in a similar manner it was pointed out that some general influence must be involved: Earlier McCay and his associates (2) had indicated that tumors of the rat are similarly inhibited. Other workers have extended the observations on mammary tumors (8, 9), and the inhibitory effect of caloric restriction has been dernonstrated also for induced and spontaneous leukemias (3, 9). In all this work the control group was compared with a restricted group whose caloric intake was approximately 60 per cent or less of the ad libitum intake. This level of restriction was chosen by us because of practical considerations; it is approximately the level below which, with ordinary care, it is difficult to maintain a group of mice so that they live at least the average life span. In fact, as has been shown in previous work (4, 5), mice restricted at such a level actually live longer on the average than even those control mice that do not develop tumors. For some years we.have been carrying on a series of experiments in which more than one restricted group was ernployed; here the restricted groups differed in the degree of restriction. The first of these experiments (graded restriction of the ration) was reported in an earlier publication (4, page 339). In the present ex-