Phytoestrogens—Friend, not Foe
Phytoestrogens, or plant estrogens, are compounds found in certain plants such as grains, berries, seeds (particularly flaxseeds), and other fruits, vegetables and legumes, but most abundantly in soybeans and soyfoods. Most studies on the effects of phytoestrogens on health have focused on a type of phytoestrogen called isoflavones, which is found in soybeans and foods made from soybeans.
The most important thing to understand about isoflavones is that they are not the same as estrogen. They have a similar chemical structure to estrogen, the reproductive hormone that all mammals produce, but small differences in chemical structure can translate to significant differences in effects on health. To a large extent, these differences are due to estrogen receptors in the body.
In order to have a biological effect, estrogen needs to attach to receptors in cells. But it wasn’t until 1996 that scientists discovered that there were two types of estrogen receptors in the body. The hormone estrogen attaches with equal affinity to both. Isoflavones, on the other hand, have a strong affinity for just one of the receptors. The effects of isoflavones vary depending on which type of receptor predominates in a tissue. The result: isoflavones sometimes act like estrogen in the body, but not always. They can have anti-estrogenic effects or sometimes, no effects at all in tissues affected by the hormone estrogen.
The most important thing to understand about isoflavones is that they are not the same as estrogen.
As a result, soy isoflavones don’t appear to have the same risks for certain diseases that are associated with estrogen. We know that among women in Asia, where soy is a common component of the traditional diet, breast cancer rates are significantly lower than among Western populations. There is evidence that consuming soyfoods early in life—during childhood and/or adolescence—may lower lifetime risk for breast cancer. Consuming soy has also been linked to improved survival in women with breast cancer. The American Institute for Cancer Research and American Cancer Society have concluded that soyfoods can be safely consumed by breast cancer patients and the World Cancer Research Fund International has concluded there may be a link between soy intake and better survival from breast cancer.
In addition to breast cancer, isoflavones have been associated with reduced risk for prostate cancer, improved cardiovascular health, favorable effects on, reduction in the frequency and severity of hot flashes, and perhaps even a decrease in wrinkles.
In contrast to the extensive research on phytoestrogens and breast cancer and other diseases, very little research has evaluated the impact of these compounds on endometriosis. Just a few studies, focusing on soy isoflavones, have been conducted. A small observational study in Japan looked at the effects of soyfood consumption among 138 women who were seeking treatment for infertility. The researchers assessed soy intake by measuring the amount of isoflavones in the subjects’ urine. Women with the highest intakes of soy isoflavones had the lowest incidence of advanced endometriosis.
One risk factor for endometriosis is increased endometrial thickness. A recent statistical analysis of 23 intervention studies found no effect of isoflavones on endometrial thickness in postmenopausal women. In one laboratory study, isoflavones had a weak estrogenic effect on endometrial tissue, but when the hormone estrogen was added to the mix, the isoflavones had anti-estrogenic effects. That might suggest an advantage for premenopausal women who are still producing estrogen.
Overall, there is clearly a need for further research before specific recommendations can be made. But based on the current research, phytoestrogens appear to be safe for women with endometriosis or who are at risk for developing it.
Since uterine tissue contains estrogen receptors and endometriosis is an estrogen-dependent disease, it is reasonable to speculate that phytoestrogens might have a similar impact in the uterus as in breast tissue. In fact, soyfoods have been associated with reduced risk of cancer of the endometrium, which is the lining of the uterus and the most common form of uterine cancer.
While the research is still evolving, it is interesting to note that increased intake of green vegetables and fresh fruit has been shown to lower risk for endometriosis while red and processed meat and trans fats can increase risk.
Choosing soyfoods over animal products and enjoying the benefits of other phytoestrogen-rich foods such as flaxseeds (which also improve gastrointestinal health and lower cholesterol) and berries (which are potent sources of antioxidants) can only be advantageous. Whether or not these compounds have specific benefits in regard to endometriosis necessitates further study. In the meantime, there is no harm and almost certainly substantial benefit to including ample amounts of phytoestrogen-rich plant foods in the diet.