Recent Analysis Explores How Soy Isoflavones May Prevent Breast Cancer

Ankeny, Iowa, July 12, 2023 (GLOBE NEWSWIRE) — Nutrition scientists have studied the role that soy foods may have in breast cancer prevention for more than 30 years, but population studies have produced inconsistent findings. However, a new analysis from Chinese researchers not only strongly suggests soy foods are protective against breast cancer but also provides an explanation for the previous inconsistent findings.

The historical low breast cancer incidence rate in Japan, a traditionally high soy food consuming country, helped spur interest in the relationship between soy and the disease. The fact that soybeans are a uniquely rich source of isoflavones, a group of naturally occurring plant chemicals, provided the impetus for researching soy foods.

This recent analysis by Yang and colleagues included 24 different observational studies from around the world. It is important to note that observational studies like those included in this analysis are not designed to establish causal relationships (or cause and effect). Having said that, several mechanisms for the proposed breast cancer protective effects of soy isoflavones have been proposed.

For these studies, researchers determined whether soy food consumers were more or less likely to develop or have breast cancer. When all studies were included in the analysis, higher consumers of soy foods were 23% less likely to report having breast cancer than the low consumers of soy foods. This finding was statistically significant, meaning the finding was unlikely to have occurred by chance. Soy was protective against both estrogen receptor positive breast cancer and estrogen receptor negative breast cancer.  That is, breast tumors whose growth are stimulated by the hormone estrogen and those that aren’t.

However, the analysis didn’t end there. When the data were sub-analyzed according to the place of origin, only in studies conducted in Asia were soy foods found to be beneficial. Researchers explored whether or not Asian women respond to soy foods differently than non-Asian women. While that is a possibility, the more likely explanation comes from another finding by Yang and colleagues. Only in studies in which the highest isoflavone intake was at least 10mg per day was soy found to be protective. In these studies, soy was associated with a 37% lower risk of breast cancer. For comparison, a serving of soymilk or tofu provides about 25mg isoflavones.

Yang and colleagues were able to show that the more isoflavones consumed, the lower the risk of having breast cancer. The authors concluded that “… dietary isoflavone intake has a protective effect on breast cancer risk, with a significant dose-response correlation, regardless of premenopausal or postmenopausal conditions.”

Soymilk and tofu have supported the eastern Asian diet for 2,000 years, and the modern iterations of soy continue to provide protein, isoflavones, and other vital nutrients. There are a variety of traditional soy foods available in the market, and including soy in your diet can be simple, like adding soymilk to your breakfast cereal or sprinkling edamame on your favorite salad.

Find more information on how to easily incorporate soy foods into daily meals at thesoyfoodscouncil.com, and learn more about the health benefits soy protein and soybean oil can offer at sniglobal.org.