THE SOY HYPE IS RIGHT. In the last few years, we are constantly reading about the seemingly endless benefits of soy products. When a food is touted in every health and nutrition column, in newspapers, magazines, and the internet, the extravagant claims are usually of questionable authenticity. But not so with soy. Epidemiological studies have shown a correlation between the consumption of soy foods and low rates of certain diseases, including coronary heart disease, hormone-dependent cancers such as breast, prostate and colon cancer, osteoporosis, and problems associated with menopause and menstrual irregularities.
Soybeans are legumes that are rich in phytoestrogens, plant-derived non-steroidal compounds that possess estrogen-like biological activity. It is the isoflavone component which is believed to provide many of the health protective effects. Isoflavones are a class of phytoestrogens that influence estrogen receptor binding, function as antioxidants, modulate sex hormone binding globulin, and exert anti-proliferative, anti-angiogenesis, and many other health promoting actions. The three main isoflavones present in soy are genistein, daidzein, and glycitin.
Epidemiological evidence suggests that populations consuming soy in fairly high amounts have lower coronary heart disease mortality. Possible mechanisms that may affect the cardiovascular system and atherosclerosis include inhibiting platelet activating factor and thrombin formation, lowering triglycerides and total cholesterol, improving arterial elasticity and inhibiting LDL oxidation.
Soy isoflavones may help prevent the development of osteoporosis at different stages. A bone-conserving action is considered to result from the direct estrogen receptor-mediated action of genistein on osteoblasts and their precursor cells. Independent of the estrogenic effects may be the enhancement of calcium absorption and retention.
A significant body of research, including epidemiological, in vitro, and animal studies, suggests that soy isoflavones may help to reduce cancer risk, specifically breast, prostate, and colon cancer. Several mechanisms have been proposed and researched include inhibition of enzymes whose actions promote cell differentiation through their effects on growth factor stimulation, inhibition of angiogenesis, and stimulation of sex hormone binding globulin.
Isoflavones are reported to exert a balancing effect on reproductive hormones in both pre- and postmenopausal women. It appears that they exert mild agonistic (estrogenic) and antagonistic (anti-estrogenic) effects, depending on the level of endogenous estrogen present. Isoflavones possess weak estrogenic activity and compete with the most potent endogenous estrogens at the receptor site, thereby reducing the total estrogen burden on the body. In this respect, the isoflavones are regarded as exerting anti-estrogenic effects.
Conversely, as natural estrogen production declines with the onset of menopause, isoflavones may help to offset this decline through their estrogenic effects. This hormonal duality is part of the reason these compounds seem to exert such a range of health effects. Theoretically, problems associated with estrogen imbalance, such as endometriosis, cervical dysplasia, breast cancer, menstrual irregularities, and symptoms commonly seen with both premenstrual syndrome and menopause, may improve with soy isoflavone intake.
Due to recent industry developments, however, one no longer must eat soy foods to get isoflavones. Several companies are now marketing soy/isoflavone pills. Given America’s proclivity for pills, it is not surprising that the supplement industry has capitalized on the excitement over the hypothesized health benefits of isoflavones. There are numerous reasons for promoting soy foods, rather than soy pills.
One is that there are other phytochemicals in soy foods, such as phenolic acids and saponins that may exert beneficial effects and that are not present in significant amounts in the pills. Two, for most people, incorporating soy foods into the diet will lead to a diet lower in saturated fat and cholesterol and higher in fiber. Three, there are potentially critical differences in isoflavone composition between the soy pills and soy foods. Four, limited dose-response data are available. Five, though results of human intervention studies remain inconclusive, there is concern that isoflavones in pill form may exert a stimulating effect on breast cancer.
Though several lines of evidence, including in vitro, animal, and human research indicate that phytoestrogens have direct beneficial effects on the arteries and bones, may reduce the risk of certain forms of cancer, and might help alleviate menopausal symptoms, the exact amount of isoflavones needed for these benefits is unknown. Finally, it must be recognized that researchers are only beginning to understand the effects of phytoestrogens. Studies have not yet clarified whether it is isoflavones in the soy foods or other components of soybeans acting alone or in conjunctions with isoflavones that are responsible for the health benefits. The health implications of these differences need to be researched and addressed.
For assistance with your dietary needs, look to medical nutrition consultant, Nancy Mazarin.