The role of soy products in reducing breast cancer risk has been a topic of investigation since the 1960s. The American Cancer Society says that evidence to support any recommendation of high soy consumption for decreasing breast cancer risk is still premature and advises people with estrogen-sensitive breast tumors or those taking tamoxifen or aromatase inhibitors to avoid consuming large amounts of soy products.
The Soybean
There are more than 2,500 varieties of soybean being grown throughout the world, and it has been a food source for more than 5,000 years. The soybean plant is native to Southeast Asia and has oblong pods containing two to four seeds or beans. Soybeans are classified as legumes and are a source of high-quality protein.
Isoflavones
Isoflavones, or phytoestrogens, are plant-based compounds that behave much like the estrogens produced in humans and animals. Isoflavones like genistein, daidzein, and glycitein are abundant in soy and believed to be responsible for many of its health benefits, such as lowering cholesterol and reducing blood pressure. Investigation of the role of isoflavones in reducing the incidence of breast cancer first began in the 1960s.
Types of Soy Foods
Soybean products come in the form of soy milk, tofu, roasted soybeans, soy powders and textured vegetable protein. The powders are used in cooking or added to drinks or shakes. Soy is available in capsule and pill form as a supplement. The isoflavones present in soy have been extracted and also made available in supplement form. However, the American Cancer Society says that most tests showing benefits from soy consumption have used whole soy protein. The amount of isoflavone present varies according to the type of soy product. Also noteworthy is that soy sauce and soybean oil do not contain soy protein or isoflavones.
Research Findings
An analysis of 18 studies conducted over the years from 1978 to 2004 and published in the Journal of the National Cancer Institute in 2006 reported that there was not enough conclusive evidence to support any recommendation for use of high-dose isoflavone supplements by women at high risk for breast cancer or by breast cancer survivors. But the article also stated that there was nothing in the data to suggest that consuming soy foods in quantities consistent with an Asian diet has a negative effect on breast health. If anything, such a diet appears to provide benefits on other aspects of health. The Shanghai Breast Cancer Survival Study conducted from 2002 to 2009 with 5,042 female breast cancer survivors between the ages of 20 to 75 years came to similar conclusions, stating that moderate soy food intake is safe and potentially beneficial for women with breast cancer.
Warning
The weak estrogen-like activity of the isoflavones in soy has led some researchers to believe that they may act as anti-estrogens and reduce cancer growth. However, the American Cancer Society says that others still contend that this estrogen-like activity could cause cancer to grow faster. Until the issue is resolved, people taking tamoxifen or aromatase inhibitors and those with estrogen-sensitive breast tumors are advised to avoid consuming large amounts of soy supplements or isoflavones.
