Soy & Breast Cancer: Does Soy Prevent Breast Cancer?

Tuesday, October 3, 2006 - 2:39pm

By Erin Dummert RD, CD

The incidence of breast cancer in Japanese women living in Japan is significantly lower than that of American women. When Japanese women move to the United States and adopt the typical American diet, their risk of breast cancer eventually matches that of American women. Japanese women consume soy foods on a daily basis, and although there are many differences in the diets and lifestyles of Japanese versus American women, researchers have identified soy foods as one possible contributing factor to the lower breast cancer rate.

What Are Soy Foods?

Soy foods are derived from soybeans. Edamame (green soybeans), soy nuts, soy milk, tofu, tempeh, and miso are traditional soy foods. In recent years, soy foods have become part of the mainstream American diet and consumers can now find a variety of soy foods at local grocery stores.

In addition to traditional soy foods, the marketplace is full of manufactured soy products including soy hot dogs, soy meat, soy cheese, soy flour, and even cereals and nutrition bars containing soy protein. These are not natural forms of soy, and therefore do not contain the same balance of nutrients. They are highly processed and for the purpose of this article are not considered soy foods.

How Soy Affects Breast Cancer Risk

Studies administered on animals and humans show that soy foods help prevent breast cancer. Soy foods contain antioxidants and beneficial plant chemicals that:

  • Protect cells from damage
  • Enhance communication between cells
  • Aid in the destruction of damaged cells.

One group of plant chemicals, known as isoflavones, is particularly prevalent in soy foods. Isoflavones produce a type of plant estrogen that is much weaker than human estrogen. Human estrogen is very strong, and has the potential to stimulate certain types of breast cancer. However, plant estrogen binds to tissues in the body, blocking the more potent human estrogen from stimulating breast cancer cells. In addition, soy foods encourage production of a chemical called Sex Hormone Binding Globulin (SHBG), which binds human estrogen, keeping it from exhibiting its harmful effects.

But isn't soy harmful if you have breast cancer?

Soy has gotten some bad press in recent years, leading people to think that it is dangerous for women with breast cancer. This reputation is undeserved, and is driven in part by a misunderstanding of plant estrogen. It is very important to note that plant estrogen is not the same as human estrogen, and it does not stimulate the body to make human estrogen.

To date, there are no reputable studies done on humans showing that soy is harmful if you have breast cancer. On the contrary, there are hundreds of studies that support the use of soy and other plant foods for reducing breast cancer risk.

Research is ongoing: in the meantime take soy to help prevent cancer

Although there are hundreds of studies that support the use of soy foods for health promotion and disease prevention, it is still too early to know with 100 percent certainty if soy foods are completely safe and beneficial for women with breast cancer. However, research on breast cancer treatment continues at a rapid pace in an attempt to answer many remaining questions about the effect of soy on breast cancer. Currently, the overwhelming body of evidence available leads most cancer nutrition experts to recommend adding soy foods to a complete cancer prevention diet.