Soy intake may be associated with a small reduction in the risk of breast cancer, according to a meta-analysis in the Journal of the National Cancer Institute.
However, because of limitations and inconsistencies in the studies examined within the meta-analysis, the authors caution that evidence is not sufficient to recommend soy as a means of preventing breast cancer.
Women in Asian countries have much lower breast cancer rates (39 per 100,000) than Western women (133 per 100,000), and when Asian women move to the United States their rates of breast cancer increase. Some studies have suggested the difference may be due to dietary habits, noting that Asian women consume higher quantities of soy products than Western women. Soybeans contain high quantities of compounds called isoflavones, molecules that affect biological pathways that could alter breast cancer risk. Because of these potential associations with lower breast cancer risk, women are increasingly taking high dose soy or isoflavone supplements.
Bruce J. Trock, Ph.D., of the Johns Hopkins School of Medicine, and colleagues conducted a meta-analysis of 18 epidemiologic studies published between 1978 and 2004 that examined the association between soy intake and breast cancer risk. Studies included women in Western countries and women in Asian countries.