Soybean & Breast Cancer: Putting Research into Practice

Written by Holli Lapes for use by health professionals

The Who What When Where Why, and How?

Who? According to the American Cancer Society, statistics indicate that a woman in the United States has about a 1 in 36 chance of dying from breast cancer. Furthermore, about 1 in 8 women in the United States are at risk for developing an invasive breast cancer.

What? The soybean, a nutrient rich protein source. Recall that Isoflavones are functional compounds found in soybeans and are a type of phytoestrogen that is structurally similar to the hormone estrogen found in mammals. The isoflavones found in soybeans are genistein and daidzein.

When? When should women consume soy products? Based on a recent review of primary research, Holli Lapes, a dietetic graduate of Florida International University found that studies indicated a strong reduction in risk of developing breast cancer when the participants began consuming soybean during childhood and adolescence. Notably, other studies found reduced risk among adults (both pre and post-menopausal) who consumed soy. It may not ever be too late to add soy into ones eating pattern, but it is best to start at childhood, as research indicates early exposure is key.

Where? Women in countries such as China, Japan and Korea consume a diet rich in soy on a daily basis. These Asian populations also have the lowest breast cancer prevalence worldwide. For women in the United States, soybean is typically consumed less often. Your client may want to know where the best sources of soybean foods can be found.


Additional considerations

• Miso can be high in sodium content
• Less processed forms of soy are best, advise clients to stay away from soy protein isolates
• Supplementation with a form of concentrated soy is not recommended
• Choose organic non GMO soy

Why? Why has soy in the context of breast cancer been so confusing to consumers and health professionals alike? For over a decade, researchers have been debating the role of soy. Part of the reason that soy was tied to an increased risk of breast cancer was because of findings in animal studies. Now, there is a clearer picture about the differences between estrogen metabolism in rats and in humans.

How? How might the mighty soybean prevent the estrogen dependent cancer of the breast? The estrogen mimicking structure of soy isoflavones may compete with mammalian estrogen. There are also biological mechanisms involved that vary from person to person. Researchers are still unclear about how individual metabolism plays a role within the context of soy and breast cancer. While the estrogen debate seems to gain the most attention, let us not forget other important details of functional foods. The free radical fighting properties of isoflavones prevent carcinogenesis.


Although there is more and more research suggesting that soy is not harmful, there is still a lot of work to be done.  For starters, the exact mechanism of action of estrogens and phytoestrogens within the body are unclear. Within individual metabolism, we need more information on the metabolites of isoflavones; equol is one of the byproducts that may influence metabolism.  Another area researchers are looking into within metabolism is probiotics and their influence on intestinal flora and thus isoflavone metabolism.

Dietary patterns need further investigation, some researchers suggest that evaluating dietary patterns rather than an individual food and its nutrients could be a useful determinant for the role of diet in breast cancer prevention. Because age and the hormonal environment are an important area of breast cancer research, larger multiethnic studies with a strong research design need to be done taking this into consideration. Finally, the safety and efficacy of supplements are to be determined. As of now, concentrated forms of soy are not recommended.

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