Verdict on Soy's Benefits for Menopausal Women Still Out, Mayo Clinic Reports

ROCHESTER, Minn.--According to the November Mayo Clinic Proceedings, a meta-analysis conducted on soy isoflavones found that soy supplementation may not have the same affect as estrogen replacement therapy (ERT) in menopausal women. The research compared soy and estrogen's effects on heart disease, breast cancer, bone loss, cognitive function, hormonal changes and skin conditions.

The analysis, conducted by Ann Vincent, M.D., and Lorraine Fitzpatrick, M.D., led to the suggestion that although some studies cite isoflavones as having a cardioprotective effect, other trials indicated a lack of secondary prevention in women with established heart disease.

However, in the Oct. 5 American Heart Association's journal Circulation, researchers found that consuming soy alongside a heart-healthy diet is recommended for high-risk individuals with elevated total and LDL ("bad") cholesterol. The report's authors also did a meta-analysis, focusing on 38 clinical trials studying the effects of soy on serum lipids. Results from the meta-analysis found that soy, as a substitute for animal protein, significantly lowered blood levels of total cholesterol, LDL cholesterol and triglycerides, without affecting HDL ("good") cholesterol. To support its findings, AHA cited that the Food and Drug Administration approved a health claim and dietary intake (25 g/d) for soy in Oct. 1999.

"This is great for soy manufacturers, that the American Heart Association endorses the use of soy in a general diet," said a spokesperson for White Wave, a soy food and beverage manufacturer. "It just shows how the soy industry is growing at such a fast rate."

However, the Mayo Clinic report questioned soy's effect on other conditions besides heart health. The authors compiled studies that compared the health of American and Japanese women to study the relationship between high intakes of soy and breast cancer. According to the authors, a high consumption of soy by Asian women may lead to a low occurrence of breast cancer; however, contraindicative studies find that it is a low-fat diet that accounts for the low cancer rate. "Thus, epidemiological studies do not provide a definitive answer regarding the ability of soy to protect against breast carcinoma," the authors noted.

They also suggested that further research is needed on the safety, efficacy and dosage of isoflavones in regards to bone density loss. Furthermore, genistein, an isoflavonoid of soy, had a placebo effect on cognitive decline. Soy supplementation led to contradictory results for easing hot flashes, "one of the major reasons that women seek medical advice regarding ERT," wrote the authors, adding that these findings highlight a need for larger long-term studies for definitive conclusions.

Currently, there are no reported adverse effects linked to short- or long-term use of soy. However, Vincent and Fitzpatrick alluded that a woman who takes advantage of the "wide unrestricted availability of over-the-counter soy isoflavone pills" and consumes too much soy may be at risk for diethylstilbestrol (DES). DES is the result of consuming xenoestrogens, which are man-made and environmental estrogens similar in molecular structure to isoflavones and other phytoestrogens. Physicians gave xenoestrogens to women from 1948 to 1971 to prevent miscarriage; unfortunately, female fetuses suffered from a rare cancer, clear-cell vaginal adenocarcinoma, which caused infertility. Affected male fetuses suffered decreased sperm counts, testicular cancer and potential prostate problems.

According to the authors, more research needs to be conducted using randomized, placebo-controlled clinical dosage studies. Until then, "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," Vincent and Fitzpatrick concluded.

Mark Messina, M.D., co-author of the 1994 book, The Simple Soybean and Your Health, agreed for the most part with the report's findings. "The evidence is very premature for soy," he said. Nonetheless, he notes that the bigger issue is that ERT may put women at risk for breast cancer and that an estrogen alternative may be more appropriate. "Soy can be part of that alternative."

In the meantime, soy product sales are expected to reach $2.6 billion this year, u p from $2.1 billion the year prior, according to Soyatech Inc., a Bar Harbor, Maine-based consulting firm.

For a copy of the Mayo Clinic report, visit www.mayo.edu/publication/proceedings/2000/nov/7511sc1.pdf.