Breast cancer is the most common type of cancer in women outside of non-melanoma skin cancer, according to the Centers for Disease Control and Prevention. It killed 40,820 women in 2006 in the United States. Many women who consume large amounts of soy worry that soy could increase their chances of developing breast cancer or increase the chance that breast cancer could recur. Studies on breast cancer and soy consumption have not come to conclusive results.
Estrogen and Breast Cancer
Estrogen, the dominant female hormone produced in large quantities during a woman's childbearing years, can feed some breast cancer cells and increase their growth. Women with breast cancer often have tumors that are "estrogen receptive," meaning they contain cells called estrogen receptors that grow when stimulated by estrogen. Women with a higher lifetime exposure to estrogen may have a greater risk of developing breast cancer in their lifetime, Sprecher Institute for Comparative Cancer Research of Cornell University states.
Soy and Estrogen
Soy is a plant estrogen classified as a phytoestrogen. Soy contains a weak form of estrogen called isoflavones. Isoflavones are only a thousandth as strong as the estrogen a woman normally produces, according to Martha Weiss, M.D., of Breastcancer.org. Phytoestrogens and estrogens can occupy the same estrogen receptors in breast tumors.
Possible Benefits
Only one type of estrogen can bind to an estrogen receptor. If isoflavones bind to an estrogen receptor, that receptor can't be stimulated by human estrogen. This could actually reduce a woman's chances of developing breast cancer, since the receptors that stimulate cell growth are less stimulated to grow by the weaker isoflavones than they would be by human estrogen. Isoflavones are sometimes called "anti-estrogens" because they take the place of estrogen on estrogen receptors.
Women who eat large amounts of phytoestrogens also have lower levels of estrogen in their bloodstream and excrete more estrogen in the urine, which reduces their overall exposure to estrogen, the Sprecher Institute reports.
Concerns
Estrogen receptors on breast tumors grow in response to any type of estrogen, including isoflavones. Even though isoflavones are less potent than human estrogen, they can still stimulate the receptor cells. In addition, in post-menopausal women, soy may act more like human estrogen than it does in pre-menopausal women, registered dietitian Gloria Tsang explains on Health Castle. It's possible that eating large amounts of soy could stimulate cancer growth in post-menopausal women.
Considerations
If you have a number of risk factors for developing breast cancer, such as a family history of the disease, being overweight, taking birth control pills or hormone replacement therapy, or if you already have or have had breast cancer, talk with your doctor about soy consumption. Smoking and drinking alcohol also up your risk of developing breast cancer. Some doctors, including Dr. Weiss, recommend limiting soy foods to several times a week for patients who have had breast cancer.
References
- Vegetarian Nutrition Info: Should Women with Breast Cancer Eat Soy?
- Health Castle: Does Soy Offer a Protective Benefit Against Breast Cancer?
- Centers for Disease Control and Prevention: Breast Cancer Statistics
- Breastcancer: Soy Intake and Breast Cancer
- Cornell University Sprecher Institute for Comparative Cancer Research: Estrogen and Breast Cancer Risk
