The Jury's Still Out On Soy

Recent interest in natural products with specific health claims has increased interest in soy proteins and their potential estrogen-like effects. Soybeans are a staple in the diet of East Asian countries. In these areas with soy-enriched diets, epidemiological studies reveal lower incidences of hormone-dependent diseases such as breast and ovarian cancer along with coronary artery disease.

The soy phytoestrogens, specifically isoflavones, have been postulated to be partly responsible for this protection. As a result, there has been intense interest in the isoflavones as "substitutes" for estrogen for postmenopausal women.

Isoflavones have emerged as the most interesting class of phytoestrogens as they have potential estrogenic activity and an extensive range of biological actions.

The authors of the Mayo Clinic report looked at various studies about isoflavones and the effects they have on coronary artery disease, breast cancer prevention, bone loss, the central nervous system, the endometrium, hormonal effects, attenuation of hot flashes and the skin.

The authors concluded, "The data we have thus far are insufficient, and it is premature to draw definitive conclusions regarding the use of isoflavones as an alternative to estrogen for hormone replacement in postmenopausal women. Appropriate dosage studies with the widely available isolated isoflavones have yet to be done. Long-term benefits of isoflavones with regard to fracture prevention, prevention of hormone-dependent cancers, attenuation of memory loss, and prevention of cardiovascular disease are currently unknown. Although epidemiological and basic laboratory studies allude to the possible protective effects of soy isoflavones on specific target tissues, randomized, placebo-controlled clinical trials are necessary to address these important issues."

To date, the article states, no adverse effects of short-or long-term use of soy proteins have been reported in humans. The only adverse effects known are reported in animals.

Mayo Clinic Proceedings is a peer-reviewed and indexed general/internal medicine journal, published for 75 years by Mayo Foundation, with a circulation of 120,000 nationally and internationally.