Soy and Breast Cancer

The role of soy in breast cancer is controversial in the medical community and confusing for consumers. Does soy prevent breast cancer or does it contribute to breast cancer? For every study that supports one position, there seems to be another supporting the opposing view.

In December 2009, the Journal of the American Medical Association reported that soy food intake was inversely associated with breast cancer recurrence and mortality. The study took place in China, where natives regularly consume soy. Patients with the highest soy intake had a 29 percent lower risk of death and a 32 percent lower risk of recurrence.

On the other hand, the National Center for Complementary and Alternative Medicine (part of the National Institutes of Health) concludes that science has not identified the long-term safety of soy and its role in breast cancer is uncertain. Soy opponents argue that health claims are just a highly effective marketing campaign launched by the soy industry.

At the heart of the soy and breast cancer debate are soy isoflavones. These are disease-fighting phytoestrogens found in soy that can affect both estrogen-like and anti-estrogen actions. In other words, phytoestrogens can stimulate-or inhibit-the growth of cancer cells.

Furthermore, although Asians who eat a traditional diet have lower incidences of breast and prostate cancer than Americans, native Asians consume small amounts of fermented soy, such as miso, natto and tempeh, (fermenting soy creates healthy bacteria we need to maintain digestion and overall health). They do not eat processed soy, such as tofu or soymilk, or take soy supplements.

So, is soy safe for women with, or at risk for, breast cancer?

Last spring at the annual meeting of the American Association of Cancer Research, one of the physicians gave a presentation titled "Diet, Nutrition and Cancer: The Search for Truth". He said the evidence for many of the associations between certain foods and cancer are weak due to limitations in the studies, and that although 30 to 35 percent of cancers are avoidable, he attributes it mostly to people being overweight and inactive. As for soy, he says it may have protective properties, but the evidence is not yet convincing.

His bottom line is good advice for all of us trying to make sense of soy and other health claims: don't make conclusions based on a single study.

If you want to include soy in your diet, your best bet is to stick with whole, unprocessed soy foods as one component of a well-balanced diet.