Natural therapists (Naturopathic Medicine) have been using phytoestrogens for their patients with hormone-driven cancers for several decades. Successfully. They have had to rely on the anecdotal evidence of the patients that were successfully treated with them. It appears that phytoestrogens have been shown to be beneficial and protective.
The understanding is that phytoestrogens exert a much weaker influence in the body than the body’s own estrogen. Phytoestrogens appear to occupy estrogen receptor sites on cells, preventing stronger estrogens from the body (and also environmental estrogens termed “xenoestrogens”) from exerting their stronger influence. Through this mechanism phytoestrogens appear to prevent cancer growth and have a balancing effect on the hormonal system. This is why so many of the herbs used to treat menopause are rich in phytoestrogens.
So, let’s address soy as there is lots of conflicting information out there. Women who eat more foods containing soy after their diagnosis have better survival overall than those who eat less soy. The conclusion is based on studies that found that women had better survival when they ate diets that are rich in soy foods, as well as diets that are rich in isoflavones. The phytoestrogen components of soy have chemical structures that are called isoflavones. The main sources of isoflavones in our diet are soy foods (though some processed soy foods might not have high isoflavone contents, and are likely to contain GMOs, which should be avoided). Other beans also contain isoflavones as well.
Diet wise – soy is good, however, do not make soy the main protein in the diet. Supplements containing isoflavone are not recommended for breast cancer survivors as they may have a stronger estrogenic effect than foods, so an individual’s safety may be compromised.
Women who want to try non-hormonal alternatives should look at the available evidence and test out their options, starting with those that carry the least known risk, in order to find what works for them, engaging their health care professional in the decision making process. Foods containing phytoestrogens have been consumed by people over thousands of years and are not by themselves harmful.