Soybeans, Soy Foods, Isoflavones and Risk of Colorectal Cancer: a Review of Experimental and Epidemiological Data.

Incidence rates of colorectal cancer are relatively low in Asian populations, in which soy foods are commonly consumed. Soybeans and soy foods are an almost exclusive source of isoflavone intake. In in vitro studies, isoflavones have been shown to have various anticarcinogenic properties such as inhibition of protein tyrosine phosphorylation, induction of apoptosis, antiangiogenesis, and inhibition of DNA topoisomerase. Thus the protective role of soy foods and isoflavones in the etiology of colorectal cancer is a matter of interest. We therefore reviewed animal and epidemiological studies of colorectal cancer in relation to soybeans, soy foods, and isoflavones. Animal studies fairly consistently showed that soyfoods or isoflavones inhibited the formation of aberrant crypt foci, but did not clearly demonstrate an inhibitory effect of soy foods and isoflavones on the development of chemically-induced colorectal cancer. Several case-control studies have suggested that soy food consumption may confer a reduced risk of colorectal cancer although the findings are rather inconsistent. Most of the previous studies, especially in Japan, ascertained only the frequency of consuming selected soy foods, and thus were defective as regards the measurement of the total consumption of soy foods. Further epidemiological studies are needed to clarify the role for soy foods in colorectal carcinogenesis.