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Dietary Fibers Differ in Their Effects on Large Bowel Epithelial Proliferation and Fecal Fermentation-Dependent Events in Rats^1,2,3,

University of Melbourne Department of Medicine, The Royal Melbourne Hospital, Melbourne, Victoria, 3050, Australia

The effects of different fiber types and processing on putative protective mechanisms for colorectal cancer were evaluated. Rats were fed diets of similar nutrient balance containing either no added fiber or 10% fiber from various sources. The rate of distal colonic epithelial proliferation, measured by the metaphase arrest method, was dependent on fiber type; ranking of fibers from highest to lowest yielded the following order: methylcellulose > coarse wheat bran > fine wheat bran parboiled and extruded rice brans > no fiber (P = 0.012). Effect on stool output ranked identically. Ranking of effect on fecal pH, from most to least acidic was as follows: coarse wheat bran the rice brans > fine wheat bran > no fiber methylcellulose (P = 0.00001). Coarse wheat bran gave significantly higher fecal butyrate concentrations than did the rice brans, which in turn gave higher levels than fine wheat bran, methylcellulose and the no-fiber diet. Proximal colon epithelial proliferation was unaffected by diet although cecal short-chain fatty acid concentrations and pH were affected. Different fibers have different effects on events in the fecal environment and distal colonic epithelium. Putative protective events (increased output, low fecal pH, high butyrate, low proliferation) are not equally affected and are unlikely in themselves to allow prediction of the protective effect of a fiber.

KEY WORDS: • butyrate • large bowel • fiber • colorectal cancer • epithelial proliferation • rats

¹ Supported in part by grants from the Anti-Cancer Council of Victoria and the National Health and Medical Research Council of Australia.

² Reprints will not be available.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

Manuscript received 17 March 1994. Revision accepted 29 November 1994.

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