The effects of high-fiber diets on chemically induced colon cancer in rats

Background - The role played by dietary fibers in the tumorigenic effects of 1,2-dimethylhydrazine (DMH) on rat colons was analyzed biochemically. Methods - Rats were injected subcutaneously with 20 mg/kg per injection DMH once a week for 5 weeks, and were fed a semi-synthetic fiber-low diet (3%, control) or diets containing 20% of one of the following fibers: cellulose, soybean, and tomato peel. The rats were sacrificed 24 weeks after the first carcinogen injection. Results - Diets with high concentrations of cellulose or tomato peel significantly decreased tumor incidence (to 33% and 40%, respectively) as compared with 92% in controls. Strong relationships were found between the tumor-protective effects of the cellulose and tomato-peek diets, and the amount of feces and ODC concentrations in colon mucosa extracts. The tumor-protective effect of the cellulose diet was also related to high concentrations of beta-glucoronidase as compared to low concentrations of this enzyme in control rats. Conclusions - Only cellulose and tomato-peel dietary fibers had a significant protective effect against DMH-induced rat colon cancer. Fibers increased fecal bulk, reduce colonic transit time and thereby reduce the time during which colonic mucosa is exposed to fecal mutagens. The tumor-protective effects of dietary fibers are correlated with an increase in the concentrations of some enzymes.