RELATIVE CONTRIBUTION OF CALORIES FROM DIETARY-FAT, CARBOHYDRATE, ANDFIBER IN THE PROMOTION OF DMBA-INDUCED MAMMARY-TUMORS IN SPRAGUE-DAWLEY RATS

It is well known that caloric restriction inhibits, whereas excess cal ories promote, mammary tumorigenesis in rats. However, the relative co ntributions to carcinogenesis by calories derived from fat or from car bohydrate are not well established. To determine the relative effects of calories from fat or from carbohydrate, as well as any interaction of dietary fiber on the promotion of 7,12-dimethylbenz[a]anthracene-in duced mammary tumors, we fed isocalorically nine diets containing diff erent ratios of fat, carbohydrate, and fiber to female Sprague-Dawley rats treated with 7,12-dimethylbenz[a]anthracene (30/group). Under con ditions of isocaloric consumption, at or near ad libitum feeding, calo ries from dietary fat had approximately twofold greater promoting effe ct on final body weight and tumor incidence than calories derived from dietary carbohydrate. Dietary fiber had an inhibitory effect on tumor development, but the effect was evident only in the high-fat groups. Logistic regression analysis of tumor incidence gave beta-coefficient estimates for the relative effects of fat, carbohydrate, and fiber of 0.866, 0.189, and -4.281, respectively. Time-to-tumor analysis by the Weibull model indicated beta-estimates of .016, 3.324, and 5.825 for d ietary fat, carbohydrate, and fiber, respectively, indicating that fat shortens and fiber increases the length of time to tumor . The statis tical model derived from these results also indicates a significant sy nergistic interaction of dietary fat and carbohydrate on final body we ight and tumor incidence.