Soy has been a food staple in the Far East for thousands of years. In addition to serving as an excellent source of protein for vegetarians and anyone trying to decrease animal fat intake, soy contains isoflavones, also called phytoestrogens. Phytoestrogens, plants that have estrogen-like effects on the body, found in soy include genistein, daidzein and glycitein. Soybeans contain more isoflavones than any other food, the Linus Pauling Institute at Oregon State University reports. While phytoestrogen effects may weakly mimic those of estrogen, the two are not the same.
Similarities
Estrogen receptors exist throughout the body, particularly in reproductive tissues such as breast, uterus and prostate, but also in brain, heart and liver tissues. Estrogen binds to estrogen-receptor sites, activating certain chemical reactions within the tissues. Phytoestrogens can bind to the estrogen sites as well; they have similar effects in some cases.
Differences
Phytoestrogens do not always produce the same results as estrogens do when they bind to estrogen-receptor sites. Phytoestrogen activity is affected by its metabolism after it is consumed. Daidzein metabolizes to equol, which has a stronger estrogenic effect in the body, but only around 33 percent of people in Western countries metabolize daidzein. Taking soy capsules does not reliably decrease menopausal effects such as hot flashes, while taking estrogen does, the American Cancer Society reports. Soy, unlike estrogen, does not appear to cause a thickening of the uterine lining.
Concerns
Current research is focusing on whether consuming phytoestrogens in soy and other foods can stimulate estrogen receptors in reproductive tissue and increase tumor growth in cancer cells. Human research has not established a definite positive or negative effect for soy and reproductive cancers yet, the Mayo Clinic states. Consuming large amounts of soy could possibly worsen estrogen-dependent conditions such as endometriosis, growth of endometrial tissue outside the uterus, the Mayo Clinic states, but more studies into soy's effect on this and similar conditions is needed, since laboratory studies have not given clear answers. One study showed an increase in hypospadias, an abnormal opening on the tip of the penis, in male infants born to women who consumed large amounts of dietary soy, Mayo Clinic reports.
Benefits
Current animal testing seems to indicate that phytoestrogens such as those found in soy produce an anti-estrogenic effect when they bond to estrogen receptors in some types of reproductive tissue. Phytoestrogens lowered prostate-specific antigens, or PSA levels, in one study, and slowed the increased in PSA levels in another, the ACS states. Levels typically rise as prostate cancers grow. Soy phytoestrogens do not appear to have the same protective effect against breast cancer, at least not when taken in the adult years. Consuming phytoestrogens in childhood may have a protective effect against breast cancer in later years, the ACS reports, but more research is needed.
