THE EFFECT OF A NATURAL HIGH-FIBER DIET ON FECAL AND BILIARY BILE-ACIDS, FECAL PH AND WHOLE-GUT TRANSIT-TIME IN MAN - A CONTROLLED-STUDY

Dietary fibre possibly protects against colonic cancer by effects on b ile acid metabolism. We investigated the effect of a natural high-fibr e diet on secondary bile acid formation. Twelve healthy subjects on an habitual low-fibre diet (for 4 weeks) consumed a high-fibre menu for 10 weeks (experimental group). A control group of 10 subjects consumed their regular high-fibre diet during this period. Faecal and biliary acid composition, faecal weight, faecal pH and gut transit time were s tudied before and after 6 and 10 weeks of fibre addition. Changes in t he experimental group were compared to changes in the control group. T he concentration, but not the excretion, of the secondary faecal bile acids was reduced in the experimental group. Faecal weight increased, faecal pH dropped and gut transit time was not altered. The biliary de oxycholic acid content decreased and the cholic acid content increased after 6 weeks, but returned to baseline values after 10 weeks of fibr e addition. This study shows that a natural high-fibre diet lowers sec ondary faecal bile acid concentration through an increase in stool wei ght. The 7alpha-dehydroxylation of primary bile acids is probably not or only transiently inhibited.