Only fibres promoting a stable butyrate producing colonic ecosystem decrease the rate of aberrant crypt foci in rats

Background-Dietary fibres have been proposed as protective agents against c olon cancer but results of both epidemiological and experimental studies ar e inconclusive. Aims-Hypothesising that protection against colon cancer may be restricted t o butyrate producing fibres, we investigated the factors needed for long te rm stable butyrate production and its relation to susceptibility to colon c ancer. Methods-A two part randomised blinded study in rats, mimicking a prospectiv e study in humans, was performed using a low fibre control diet (CD) and th ree high fibre diets: starch free wheat bran (WB), type III resistant starc h (RS), and short chain fructo-oligosaccharides (FOS). Using a randomised b lock design, 96 inbred rats were fed for two, 16, 30, or 44 days to determi ne the period of adaptation to the diets, fermentation profiles, and effect s on the colon, including mucosal proliferation on day 44. Subsequently, 36 rats fed the same diets for 44 days were injected with azoxymethane and ch ecked for aberrant crypt foci 30 days later. Results-After fermentation had stabilised (44 days), only RS and FOS produc ed large amounts of butyrate, with a trophic effect in the large intestine. No difference in mucosal proliferation between the diets was noted at this time. In the subsequent experiment one month later, fewer aberrant crypt f oci were present in rats fed high butyrate producing diets (RS, p=0.022; FO S, p=0.043), Conclusion-A stable butyrate producing colonic ecosystem related to selecte d fibres appears to be less conducive to colon carcinogenesis.