Enhancement of rat colon carcinogenesis by wheat bran consumption during the stage of 1,2-dimethylhydrazine administration.

The effect on intestinal carcinogenesis of feeding a 20% wheat bran dietary supplement, either during and/or after the stage of carcinogen administration with 1,2-dimethylhydrazine, was examined in 48 male Sprague-Dawley rats fed defined diets for 31 weeks. Nutrient intake and body weight gain were equivalent in all groups of animals. In the rats fed bran during carcinogen administration, tumor yield was significantly greater. Benign and malignant tumors increased by 3.4-fold (p less than 0.005), adenomas by 3.5-fold (p less than 0.025), and adenocarcinomas by 3.25-fold (p less than 0.05) over the yield found in the group fed a fiber-free diet. Consumption of wheat bran, after completion of carcinogen exposure, reduced the yield of benign adenomas by 71.4% when compared with the group fed the fiber-free diet (p less than 0.025). Those rats fed a wheat bran supplement during carcinogen administration and then switched to a fiber-free diet afterwards had the highest tumor yield, 4.5 times as many benign and malignant tumors as in those rats consistently fed the fiber-free diet (p less than 0.05) and at least 6 times as many adenomas as any of the other dietary groups (p less than 0.05). These results demonstrate that dietary wheat bran, a fiber which produces a hyperproliferative response in the colon, significantly increases colon carcinogenesis when fed to rats during the stage of carcinogen administration. This effect appears to be further enhanced when the wheat bran is totally removed from the diet following the stage of carcinogen administration. These data indicate that the hyperproliferative effects of wheat bran appear to outweigh any preventive actions that bran may have on colon carcinogenesis by altering the bulk of intestinal contents and their transit time through the bowel.