Effect of long term lactulose ingestion on secondary bile salt metabolism in man: potential protective effect of lactulose in colonic carcinogenesis.

This study investigated whether colonic absorption of secondary bile acids, especially deoxycholate in patients with adenomas could be decreased by oral lactulose. Bile acid metabolism was studied using bile sampling and 14C-deoxycholate kinetics in patients with colonic adenomatous polyps before and after four and 12 weeks of lactulose, 60 g/day. The results indicate that lactulose decreased the deoxycholate pool size from a mean of 22.0 (SD: +/- 13.8) to 14.3 (+/- 7.6) mumol/kg (p less than 0.025). Deoxycholate absorption fell from 3.8 (+/- 2.3) to 2.9 (+/- 1.4 mumol/kg/d (ns). The biliary bile acid composition decreased significantly in deoxycholate after four and 12 weeks with a rise in primary bile acids. There was a highly significant correlation between the %-change in DCA input and the %-change in DCA pool size (r = 0.89). Intestinal transit measured by the pellet method (4.1 +/- 1.9 to 2.4 +/- 0.6 day; p less than 0.01) and faecal pH decreased, while stool frequency and weight rose significantly. Significant correlations between the %-change in gut transit time and the %-change in DCA pool size or %-change in DCA input were absent. The results show that it is possible to lower colonic secondary bile acid absorption by long term lactulose feeding. This effect can be mediated by accelerated transit and the acidification of the colonic contents.