Confused about soy isoflavones, soy foods and risk of breast cancer? A recent study concluded that natural phytoestrogens including isoflavone compounds derived from soy and other plants reduce breast cancer recurrence and improve survival. Results from a study conducted at Johns Hopkins Kimmel Cancer Center, “Phytonutrients and outcomes following breast cancer: a systematic review and meta-analysis of observational studies.” were published in January 2024.
Researchers concluded that soy isoflavones were associated with a 26% reduced risk of breast cancer recurrence among post-menopausal women breast cancer survivors. The most significant results were realized at 60 milligrams per day.
Soy contains isoflavone compounds including genistein and daidzein. Isoflavones are phytoestrogens, that have a similar structure to human 17-β estradiol hormone. Phytoestrogens bind to and mildly activate estrogen receptors and act as selective estrogen receptor modulators. Phytoestrogens block the binding of native estrogen and thus block the effects of human estradiol. Phytoestrogens exert a very mild effect on estrogen activation compared to human estradiol. Therefore, there is less estrogen activation and signaling in the presence of isoflavone phytoestrogens.
Another review, Soy Isoflavones and Breast Cancer Risk: A Meta-analysis, conducted by Ioannis Boutas, et al in 2022 concluded, “The consumption of soy isoflavones can reduce the risk of breast cancer in pre-menopausal and post-menopausal women.”
A review conducted in 2023, .” Benefits of Soybean in the Era of Precision Medicine: A Review of Clinical Evidence, Jung Hyun Kang, et al, examined the current clinical evidence focusing on the benefits and risks of soybean ingredients and concludes “In breast, prostate, colorectal, ovarian, and lung cancer, epidemiological studies showed an inverse association between soybean food intake and cancer risks. Soybean intake was inversely correlated with risks of type 2 diabetes mellitus (T2DM), and soy isoflavones ameliorated osteoporosis and hot flashes. Notably, soybean was one of the dietary protein sources that may reduce the risk of breast cancer and T2DM.”
Additionally, as early as 2010 Dr. Mary Hardy MD of UCLA Simms Mann Center for Integrative Oncology, Dr. Donald Abrams MD of UC San Francisco Center for Integrative Medicine and Dr. Mark Messina, Ph.D., professor of nutrition a Loma Linda University, CA, co-authored a paper, Can clinicians now assure their breast cancer patients that soyfoods are safe? (Women's Health (2010)6(3), 335–338, addressing the confusion that exists among physicians and patients regarding the health consequences of soy foods and soy isoflavones. In this paper they identify soy isoflavones as selective estrogen receptor modulators. They conclude that it is safe for women to include whole, minimally processed soy foods including tofu, soy milk, whole soybeans (like edamame), miso, soy yogurt, and tempeh, in their diets, but that soy foods and soy isoflavones should not be considered as treatment for breast cancer.
There is now a clear body of evidence not only demonstrating the safety of phytoestrogens contained in soy and other botanicals, but also their benefits which include the potential reduced risk and reduced recurrence of breast cancer, support for control of menopausal symptoms such as hot flashes and osteoporosis as well as reduced risk of Type 2 Diabetes.