Many plants contain compounds that behave like estrogens, the female sex hormones. Because only animal bodies can produce true hormones, these plant chemicals are called hormonelike compounds or phytoestrogens (plant estrogen). Seems fair.
The three kinds of phytoestrogens are i Isoflavones, in fruits, vegetables, and beans i Lignans, in grains i Coumestans, in sprouts and alfalfa
The most-studied phytoestrogens are the isoflavones known as daidzein and genistein (found in soy), two compounds with a chemical structure similar to estradiol, which is the estrogen produced by mammalian ovaries.
Like natural or synthetic estrogens, daidzein and genistein hook onto sensitive spots in reproductive tissue (breast, ovary, uterus, prostate) called estrogen receptors. But phytoestrogens have weaker estrogenic effects than natural or synthetic estrogens. It takes about 100,000 molecules of daidzein or genistein to produce the same estrogenic effect as one molecule of estradiol. Every phytoestrogen molecule that hooks onto an estrogen receptor displaces a stronger estrogen molecule. As a result, researchers suggested that consuming isoflavone-rich foods such as soy products may provide post-menopausal women with the benefits of estrogen (stronger bones and relief from hot flashes) without the higher risk of reproductive cancers (of the breast, ovary, or uterus) associated with hormone replacement therapy (HRT). The theory was supported by the fact that the incidence of breast and uterine cancer, heart disease, osteoporosis, and menopausal discomfort is lower in countries where soy — a primary source of phytoestrogens — is a significant part of the diet.
However, recent animal and human studies offer conflicting evidence. On the one hand, these studies
1 Raise questions about the safety of phytoestrogen-rich foods for women with hormone-sensitive tumors
1 Show that phytoestrogen may stimulate tumor growth in animals whose ovaries have been removed
1 Demonstrate that isoflavone-rich foods have only modest effects on preserving bone and relieving "hot flashes" at menopause
One the other hand, including isoflavone-rich soy foods such as tofu, miso, tempeh, soy milk, soy flour, and soy protein in a healthful diet
1 May reduce total cholesterol, lower LDL ("bad cholesterol"), and maintain or even increase blood levels of HDL ("good cholesterol"). In 2005, researchers at the Johns Hopkins University School of Nursing announced the results of a 216-woman study funded by the National Heart, Lung, and Blood Institute in which women consuming 20 grams of soy proteins per day had significant decreases in LDLs, while women who were given the same amount of milk protein did not.
1 Helps people feel full longer so they can stick to a lower-calorie diet for managing weight loss.
Bottom Line? According to the International Food Information Council, "Further clinical studies will continue to increase understanding of the role of soy in maintaining and improving health." Couldn't have said it better myself.
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