Failure to inhibit the formation of mammary carcinoma in mice by intermittent fasting.

Chronic restriction of caloric intake inhibits the formation of various types of tumors in the mouse. This inhibition is evidenced both by a decrease in the proportion of mice developing tumors and by a delay in the time at which the tumors appear (4-6, 8, 11, 15, 16). The magnitude of the inhibi tory effect is dependent on the degree of caloric re striction (1, 10, 14), the type of tumor (11), the dosage or potency of the carcinogen (12), and on whether the restricted caloric intake is maintained during the stage of initiation or the stage of devel opment of the tumor (9). In all these studies the daily dietary restriction of caloric intake was con tinued for months—in some instances for almost the whole life span of the mice. The question arose as to whether continued daily caloric restriction is necessary to inhibit the formation of tumors or whether comparable effects might be observed in animals subjected to intermittent fasting. The fol lowing experiment was planned to determine the effect of fasting for 24-hour periods twice weekly, with no other limitation of food intake.