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 commonlyconsumed. Soybeans and soy foods are an almost exclusive source of isoflavone intake. In in vitro studies, isoflavoneshave 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 foodsand isoflavones in the etiology of colorectal cancer is a matter of interest. We therefore reviewed animal andepidemiological studies of colorectal cancer in relation to soybeans, soy foods, and isoflavones. Animal studies fairlyconsistently showed that soyfoods or isoflavones inhibited the formation of aberrant crypt foci, but did not clearlydemonstrate an inhibitory effect of soy foods and isoflavones on the development of chemically-induced colorectalcancer. Several case-control studies have suggested that soy food consumption may confer a reduced risk of colorectalcancer although the findings are rather inconsistent. Most of the previous studies, especially in Japan, ascertainedonly the frequency of consuming selected soy foods, and thus were defective as regards the measurement of the totalconsumption of soy foods. Further epidemiological studies are needed to clarify the role for soy foods in colorectalcarcinogenesis.