INFLUENCE OF STARCH FERMENTATION ON BILE-ACID METABOLISM BY COLONIC BACTERIA

Secondary bile acids (BA) may be involved in the pathogenesis of color ectal cancer. In vivo, starch malabsorption has been shown to reduce f ecal excretion of secondary BA. The present in vitro study was perform ed to investigate the effect of starch fermentation on BA metabolism b y colonic bacteria. Fecal samples of healthy volunteers were incubated in anaerobic batch cultures for 48 hours with the primary bile acids cholic (0.6 g/l) and chenodeoxycholic acid (0.4 g/l). Media were starc h free or enriched with starch (10 g/l). The pH was controlled and hel d at 6 or 7. In the starch-free incubations, secondary BA were rapidly formed, and degradation of primary to secondary BA was complete withi n 24 hours. The formation of secondary BA was partially inhibited by t he addition of starch to the media. This effect was stronger at pH 6 t han at pH 7. Starch was rapidly and completely fermented. In conclusio n, this study showed that formation of secondary BA by fecal bacteria is inhibited when starch is simultaneously fermented, an effect that i s mainly, but not completely, explained by reduction of pH.