Estrogen is a hormone that plays important roles in both men and women. Phytoestrogens include compounds in soy such as lignans and isoflavones that have weak estrogenic activity when eaten by humans. No serious adverse effects from phytoestrogens have been observed. Although phytoestrogens have been promising in improving bone growth, cholesterol levels and fighting hormone-associated cancer, results have been inconsistent.
Estrogen in the Body
In addition to its role in female reproduction and secondary sex characteristics, estrogen has a variety of roles in both men and women. Estrogens stimulate the expression of genes necessary to maintain lipid levels in the blood, regulate water and salt balance, increase bone density, improve elasticity of skin and blood vessels and regulate the normal function of the heart, lungs and brain. Estrogen is necessary for fertility in both sexes.
Metabolism
Isoflavones and lignans are metabolized by naturally-occurring bacteria in your intestines. The level of estrogenic activity depends on how they are metabolized, potentially varying significantly between individuals. According to the Linus Pauling Institute at Oregon State University, only about a third of Western populations metabolize soy isoflavones to highly estrogenic metabolites, substances that are involved in the metabolism process. Fermented soy products such as soy sauce and miso may increase the rate in which isoflavones and lignans enter the bloodstream. This variability may potentially explain the mixed results of research studies about the risks and benefits.
Soy May Raise or Lower Estrogen Signaling
The phytoestrogens of soy in your body typically have a much lower attraction to the estrogen receptor than estrogens naturally produces by your body. If no estrogen is present, the estrogen receptor will be weakly activated. If estrogen is present, signaling will be lower than normal as endogenous estrogens compete for available receptors with the soy phytoestrogens. Some metabolites of phytoestrogens may also inhibit the estrogen receptor.
Benefits
Soy phytoestrogens have been investigated to see if they can be useful in treating hormone-associated cancer such as breast, endometrial or prostate cancer. There is no consistent research evidence to support any risk or benefit of soy. Phytoestrogens may also be beneficial in preventing osteoporosis and cognitive decline in post-menopausal women. Weak evidence supports the benefit of soy phytoestrogens in improving lipid and cholesterol levels in the blood in those at risk for cardiovascular disease.
Risks
Soy phytoestrogens have been consumed as major parts of the diet without any evidence of significant health risks. According to the Linus Pauling Institute, up to 100 mg per day of soy isoflavones appear to be safe for six months. Long-term studies have not been performed to demonstrate any health benefit or risk of soy phytoestrogens. It's unlikely that the intake of soy could cause symptoms of hyperestrogenemia, or pathologically high estrogen levels.
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