Soy and Breast Health

I am often asked about the health benefits of soy. Are soy products, which have entered the mainstream food supply, beneficial to most women? The answer is yes.

So why do we read that soy isn’t healthful for all women? There has been widespread debate about soy products and their effects on health, particularly breast health. The results of studies have shown conflicting results, but continuing research on the subject is helping to clarify some issues.

For example, there is a body of research showing that soy is beneficial to your heart because it lowers triglycerides and cholesterol, particularly LDL, or “bad” cholesterol. There is also evidence that soy may support bone health by inhibiting bone resorption, or calcium loss from your bones. In addition, soy products have been shown to ease menopausal symptoms such as night sweats and hot flashes.

The controversy about soy generally centers around breast health. Studies on how soy affects a woman’s breast tissue have looked at the estrogen-like effects of the soy-derived isoflavones genistein and daidzein. However, these isoflavones have weak estrogenic properties compared with the estrogen naturally produced by a woman’s own body.

A recent article in Advanced Practice in Acute Critical Care points to some studies of women in Asia, in which Asian women who consumed a high amount of soy in their diets had a lower risk of breast cancer than Western women. Interestingly, these studies also found that when Asian women move to the West and adopt the typical Western diet, their breast cancer risks go up.

Epidemiological studies suggest that diets with high concentrations of soy isoflavones are associates with a reduced risk for breast cancer.

Interestingly, other studies have associated lowered risk of adult breast cancer with adolescent consumption of isoflavone-rich soy. In other words, the age of exposure to isoflavones may be an important factor in reaping their protective benefits. Still, animal and test-tube studies on soy isoflavones have shown that they could increase the proliferation of breast cancer cells.

A study published in the May 2005 journal Carcinogenesis offers still another viewpoint. The authors suggest that a lot depends on how one ingests soy. They found that when the isolated soy isoflavone genistein was consumed, breast tumor growth was stimulated. This was not the case when whole soy food products were ingested. Because soy products in Asian countries are minimally processed, most women in Asia eat whole soy foods. In the United States, however, many women frequently consume processed soy products. These processed soy products contain large amounts of isoflavones in the form of genistein capsules or powders. What’s missing? Processed soy lacks any biologically active compounds found in whole soy foods.

Here’s the good news: products made with whole soy foods are widely available. These include tofu, tempeh, soy flour, miso soup, soybeans (edamame), soy protein powder, and soymilk. Soy products, preferably organic, should be part of every woman’s plan for creating optimal health. Among the many positive qualities, soy contains compounds that can block estrogen receptors, inhibit enzymes that can induce cancer, and act as antioxidants.

Dr. Laurie Steelsmith ( is a naturopathic physician and licensed acupuncturist with a private practice in Honolulu, Hawaii. She is author of the critically acclaimed book, Natural Choices for Women’s Health: How the Secrets of Natural and Chinese Medicine Can Create a Lifetime of Wellness (Three Rivers Press, 2005).