Soy is derived from the soya bean, a cholesterol-free legume that is high in protein and low in saturated fat. Soy has a high-fiber content and contains an abundance of vitamins and minerals, including calcium, iron, potassium and zinc. Soy is rich in B vitamins and a good source of omega-3 essential fatty acids. It is present in many foods, including meat products and meat substitutes, cereals and baked goods. Although soy is recognized for its health benefits, the isoflavones in soy may disrupt hormones.
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Soy is a phytoestrogen that mimics the body's naturally occurring hormone functions. The thyroid gland, which is responsible for the production and storage of hormones that control all of the body's systems, can be disrupted by phytoestrogens. Thyroid hormones regulate heart rate, balance blood pressure, maintain body temperature and maintain the appropriate metabolic rate for converting food to energy. Because soy mimics some hormones, it may interfere with certain thyroid medications. According to Dr. Todd B. Nippoldt of The Mayo Clinic, "Soy has long been thought to interfere with the body's ability to absorb the medication. However, there's no evidence that people who have hypothyroidism should avoid soy completely."
Estrogen, produced in the ovaries, is responsible for the development of female sexual and reproductive organs. It is the estrogen-mimicking plant compounds found in soy that are responsible for soy's health benefits. But these same estrogenic compounds, known as isoflavones, can have a negative effect on female hormones when consumed in large amounts. Laboratory studies show that genistein, a phytoestrogen found in soy, may lead to a decline in fertility, ovulatory dysfunction and irregular menstrual cycles. According to a study from the National Institute of Environmental Health Sciences, published in the April 31, 2011 issue of "Reproductive Toxicology," studies "clearly demonstrate that environmentally relevant doses of genistein have significant negative impacts on ovarian differentiation, estrous cyclicity, and fertility in the rodent model. Additional studies of reproductive function in human populations exposed to high levels of phytoestrogens during development are warranted."
Estrogen increases during pregnancy in order to meet the growing demands of both mother and fetus. Estrogen production is maintained by the ovaries and the placenta. During pregnancy, it is the hormone responsible for uterine growth, thickening of the uterine lining, increasing blood volume, milk production and the development of fetal organs. Because the isoflavones in soy mimic estrogen, it is possible that eating large amounts of soy may result in a hormonal imbalance during pregnancy. According to reporter Lindsey Konkel from "Scientific American," "There's strong evidence from animal studies that the isoflavone genistein alters reproduction and embryonic development."
When estrogen levels begin to fall during menopause, the normal balance of hormones becomes disrupted. A myriad of symptoms may accompany the drop in estrogen, including hot flashes, night sweats, loss of memory and irritability. Many women are wary of beginning hormone replacement therapy because of the risks associated with it. Instead, they opt for natural alternatives like soy supplements. According to MayoClinic.com, "Overall, evidence suggests that soy products containing isoflavones may help reduce menopausal symptoms, such as hot flashes. More study is needed to confirm this use."
- What to Expect: Estrogen and Progesterone
- "Scientific American"; Could Eating Too Much Soy Be Bad For You?; Lindsey Konkel; Nov. 3, 2009
- MayoClinic.com: Soy Allergy
- "Reproductive Toxicology"; Circulating Levels of Genistein in the Neonate, Apart From Dose and Route, Predict Future Adverse Female Reproductive Outcomes; W.N. Jefferson, et al.; Apr. 31, 2011
- MayoClinic.com: Soy
- MayoClinic.com: Hypothyroidism (underactive thyroid); Todd B. Nippoldt, M.D.