Protective role of lactulose in intestinal carcinogenesis.

Primary bile acids are converted to carcinogenic secondary bile acids by colonic bacteria when the colonic pH is high. Therefore acidification of the luminal contents may reduce the cancer risk. The ability of lactulose to reduce colonic pH, secondary bile acid production, mucosa crypt cell production rate and tumour formation was measured in a rat model of intestinal carcinogenesis. Eighty Wistar rats were divided into four groups receiving normal diet alone or with lactulose, azoxymethane or both azoxymethane and lactulose. The addition of lactulose was associated with a significant fall in small intestinal and colonic pH. Lactulose was associated with a sharp rise in the secondary to primary bile acid ratio. The crypt cell production rate fell significantly with lactulose. The addition of lactulose was associated with a significantly reduced tumour yield in small intestine but not in colon. Lactulose therefore can reduce this is of no value in humans at risk of developing colorectal carcinoma.