Phytoestrogens are sterol molecules found in plants that have been shown to have both estrogenic (estrogen like) and antiestrogenic properties. There are over 1000 known. In general, all but a few of these sterol molecules exert a very weak level of estrogenic activity, Of these plant compounds and the metabolic products they produce in humans, two main categories exist: isoflavones and lignans.
A wide range of commonly consumed foods contains amounts of these different Phytoestrogens. For example, soy, garbanzo beans and other legumes, which are most often consumed in products like tempeh, miso and tofu, are a particularly good source of the isoflavones genistein and daidzein. Lignins are a constituent of the cell wall of plants with the highest amounts found in the husk of seeds used to produce oils, such as flaxseed.
Coumestans, another category of Phytoestrogen, which are between 30 and 100 times more potent than isoflavones, can be found in high concentration in sunflower seeds and bean sprouts.
Today, we now know from human clinical trials and molecular and cellular biology experiments that certain phytoestrogens can confer notable health benefits related to cardiovascular diseases, including the lowering levels of blood cholesterol, cancer by inhibiting several stages of cancer initiation and progression, osteoporosis via stimulating osteoblasts (ipriflavone), menopausal symptoms and maintaining prostate health in men, which is in part validated by the epidemiological evidence that the rates of these conditions are more favourable in both men and women, among populations that consume diets containing a higher proportion of plant derived foods. Dietary phytoestrogens also dilute xenoestrogen-type carcinogens by binding at the alpha and beta estrogen receptors (ERα + ERβ) found in many cells and acting as anti-estrogens.
Ongoing research into the use of Phytoestrogens as nutraceuticals (not as the basis for pharmaceutical products) continues to discover beneficial dietary therapies. For example, highly effective management of menopausal symptoms and reduction in long term health risk presented by estrogen deficiency is possible via phytoSERMs (SERM - selective estrogen receptor moderator). A SERM selects specific estrogen receptors in the body and either stimulates or suppresses an estrogen-like response, thus causing beneficial activity in tissues such as bone and skin, while preventing excessive estrogen-like responses in other parts of the body, such as the breast and endometrium.
An example of a phytoSERM is FX menopause, developed for menopause management; an example of a pharmaceutical SERM is Tamoxifen, an important treatment for breast cancer.
Women being treated for estrogen dependent cancers and, most importantly breast cancer should not assume that concentrated supplements containing phytoestrogens are safe to use. Although often mild in action when compared to conventional HRT, phytoestrogens function physiologically by binding at the estrogen receptors found in many cells, including both breast and endometrial tissue, promoting or moderating estrogenic activity and have the potential, by doing so, to block the activity of therapies design to stop estrogenic activity e.g. Tamoxifen.
A continuous high intake of supplements containing phytoestrogens is not recommended if pregnant, using contraceptives (excluding UID) or full dose HRT, undergoing fertility treatments or with low blood pressure (Low blood pressure is where it is less than 90/60mmHg), estrogen or over-active thyroid related disorders or using blood thinners / anticoagulants, e.g. warfarin.