The intestinal microflora and its colon cancer connection.

Epidemiologic studies suggest that the incidence of colon cancer is influenced by environmental factors, especially diet. The high beef-high fat-low fiber diet of Western societies is associated with a high risk of colon cancer. The intestinal microflora may play a role in colon cancer by metabolic activation of procarcinogens in the lumen of the large bowel. The link between diet and colon cancer can be explained, in part, by the alterations in fecal bacterial enzyme activity induced by a Western-style diet. For example, fecal bacterial beta-glucuronidase, nitroreductase, azoreductase and steroid 7-alpha-dehydroxylase activities are increased in animals or humans consuming a high beef diet. These enzyme activities can be reduced by eating a grain diet, by the addition of Lactobacillus acidophilus to the diet, or by administration of low dose antibiotics. In experimental animals these three measures to reduce the activity of the microflora also produce few colon tumors in animals given the chemical carcinogen dimethylhydrazine. Further studies are needed to establish whether alterations in the metabolism of the colonic microflora can reduce the risk of large bowel cancer in humans.