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Relationship between Colonic Luminal pH, Cell Proliferation, and Colon Carcinogenesis in 1,2-Dimethylhydrazine Treated Rats Fed High Fiber Diets¹

Division of Gastroenterology, Department of Medicine, University of California, Davis, California 95616

The comparative effects of different fibers on colonic luminal pH, crypt cell proliferation, and colon carcinogenesis were studied in 120 male Sprague-Dawley rats. The animals were divided into five equal groups and fed either a basal fiber free diet or the basal diet supplemented with 10% pectin, cellulose or guar, or 20% oat bran for up to 30 weeks. 1,2-Dimethylhydrazine was given at 20 mg/kg body weight as a weekly s.c. injection for 12 weeks. Food intake and weight gain were similar in all diet groups. At sacrifice, in vivo pH measurements showed that compared to fiber free rats, all fibers significantly acidified large bowel luminal contents (P < 0.05). In the guar group 62.5% of rats developed colonic tumors compared to 33.4% of the fiber free rats (P < 0.05). The yield of proximal colonic adenocarcinomas in the oat bran, pectin, and guar groups was increased by 4.5 to 5 times over the fiber free level (P < 0.05–0.025). Pectin and guar provided the greatest stimulus to cell proliferation. A lower luminal pH was associated with a higher tumor yield and increased epithelial cell proliferation. Thus, acidification of colonic contents by high fiber diets failed to inhibit rat colon carcinogenesis, while the consumption of soluble fibers, such as oat bran, pectin, and guar, was associated with enhancement of proximal colon carcinogenesis.

¹ This work was supported by USPHS Grant CA 35627 from the National Cancer Institute and was presented in part at the annual meeting of the American Association for Cancer Research, May 1985, Houston, TX, and appeared in abstract form (1).

² To whom requests for reprints should be addressed, at Division of Gastroenterology, Department of Medicine, TB 192, University of California, Davis, CA 95616.

³ Present address: Department of Animal Science/Nutrition, Texas A & M University, College Station, TX 77843.

Received 6/28/85. Revised 12/12/85. Accepted 12/23/85.