Effects of diet on the fecal excretion and bacterial modification of acidic and neutral steroids, and implications for colon carcinogenesis.

Diet-induced changes in the excretion and fecal concentration of bile acids have been associated with enhancement or reduction of chemically initiated colon carcinogenesis in experimental animals. Dietary lipid increases the excretion and fecal concentration of bile acids. Certain types of dietary fiber such as pectin and lignin also increase fecal sterol output. However, the predominant effect of food-derived fiber (e.g., wheat brain) is to increase stool bulk and, hence, reduce the concentration of fecal sterols. Although it has been suggested that the tumor-promoting activity of bile acids is enhanced following bacterial dehydroxylation, dietary factors appear to have limited effect on bacterial flora or acidic sterol degradation in the colon.