Soy helps fight breast cancer?
WHAT THEY’RE SAYING
Because of its role in influencing sex hormone metabolism and biological activity, high intake of soy isoflavones results in lower incidence of breast cancer and other common cancers.
WHAT WE KNOW
Soy foods or soy products are a rich source of isoflavones, which present both weak estrogenic and anti-estrogenic effects.1 Premenopausal women are greatly different from postmenopausal women in endogenous (natural) estrogen level; breast cancer is a disease closely associated with this hormone. Therefore, menopausal status may play a role in the soy isoflavone-breast cancer association.2
Isoflavones are related to isoflavonoids, which is a class of flavonoids. Flavonoids, a subclass of polyphenols, is a group of phytochemicals that are among the most potent and abundant antioxidants in our diet. Polyphenols are thought to protect the body’s tissues against oxidative stress and may prevent various diseases such as cancer, cardiovascular disease, and inflammation.
Reviewed studies have shown soy isoflavone/soy food intake has an influence on breast cancer risk among Asian women, but this association did not exist among Western women.
HOW DO WE KNOW THIS
A review of 30 studies’ results for premenopausal women and 31 studies for postmenopausal women suggested that high soy isoflavone intake presents some protective effects on breast cancer for both pre- and post-menopausal Asian women (most recent study January 2013).3
Analysis of these studies concluded that soy isoflavone/soy food intake was inversely associated with breast cancer risk among Asian women, but this association did not exist among Western women.1 It appeared that soy isoflavone intake had no influence on breast cancer risk among pre- and post-menopausal women in Western countries. Exposure to soy isoflavone in early life and high intake level may be important contributing elements for its protective effect in Asian women (pre- and post-menopausal). And non-association between soy isoflavone intake and breast cancer risk among Western pre-and post-menopausal women may be related to their low intake levels of soy.4
Soy provides a rich source of antioxidants, which may protect cells from damage caused by the by-products (free radicals) of everyday metabolism and toxic substances in the environment and food. Making soy part of life early on may enhance its protective qualities. But stick with whole foods!
For the highest amount of isoflavones (antioxidants), stick with whole soybeans, tempeh, soymilk, tofu, soy nuts, natto, or okara.
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Lee H.P., L. Gourley, S.W. Duffy, et al. (1991) “Dietary effects on breast-cancer risk in Singapore.” Lancet
337: 1197–1200. doi: 10.1016/0140-6736(91)92867-2. View Article
Dong, J.Y., L.Q. Qin. (2011) “Soy isoflavones consumption and risk of breast cancer incidence or recurrence: a meta-analysis of prospective studies.” Breast Cancer Res Treat
125: 315–323. doi: 10.1007/s10549-010-1270-8. View Article
Chen, Meinan, Yanhua Rao, Yi Zheng, et al. (2014) “Association between Soy Isoflavone Intake and Breast Cancer Risk for Pre- and Post-Menopausal Women: A Meta-Analysis of Epidemiological Studies.” PLOS One
, Feb. 20, 2014. DOI: 10.1371. View Article
Messina, M. (2004) “Western soy intake is too low to produce health effects.” American Journal of Clinical Nutrition
80: 528–529. View Article