DIETARY GUAR GUM ALTERS COLONIC MICROBIAL FERMENTATION IN AZOXYMETHANE-TREATED RATS

To assess the effects of guar gum on colonic microbial fermentation an d cancer development, azoxymethane-treated rats were fed a partially h ydrolyzed guar or control diet. Anaerobic fecal incubations were condu cted at 8-wk intervals, either without added substrate or with cornsta rch or hydrolyzed guar as substrates. Short-chain fatty acids in colon ic contents and colonic carcinoma areas were measured at 27 wk. Fecal in vitro fermentation rates were higher for guar-fed rats than for con trol rats [three-way ANOVA (diet, time, in vitro substrates), P = 0.00 2]. Fecal in vitro butyrate production was greater for guar-fed rats t han for control rats after 3-11 weeks of diet treatment (three-way ANO VA, P = 0.027). Butyrate concentrations of colonic contents at 27 wk w ere higher in guar-fed than in control rats and higher in the cecum th an in the post-cecal colon (two-way ANOVA, P = 0.0001). A regression e quation predicting colonic carcinoma area (r(2) = 0.279) using propion ate and butyrate concentrations of the contents of the post-cecal colo n showed propionate as a positive predictor (P < 0.001) and butyrate a s a negative predictor (P = 0.033). Our results show that patterns of short-chain fatty acid production may affect the results of fiber-carc inogenesis experiments. Dietary addition of hydrolyzed guar is associa ted with fecal fermentation low in propionate and high in butyrate; sh ort-chain fatty acid concentrations are greater proximally than distal ly. These results suggest that butyrate protects against colonic neopl asia, whereas propionate enhances it, and demonstrate that colonic mic robiota adapt to produce more butyrate if given time and the proper su bstrate.