Edition: U.S. / Global

Personal Health

By Jane E. Brody
Published: August 27, 1997

AMERICAN women were once thought to be wimps about menopause. After all, women in Japan and other Asian countries rarely complained about hot flushes and other menopausal symptoms that had to be ameliorated by estrogen therapy. Why should American women be different?

In the last two decades, a possible dietary explanation for the difference has emerged, and that has pointed the way toward a new approach to treating menopausal symptoms. Dietary habits in Asian countries might also help account for the lower rates of heart disease and breast cancer there.

Asian diets contain large amounts of plant-produced chemicals that when changed by enzymes from intestinal bacteria, have a weak estrogenic effect. Soybeans and products made from soybeans, which constitute a large part of many Asian diets, are especially rich in these phytoestrogens called isoflavones. Depending upon a person's own estrogen production and the tissue in question, the weak estrogenic effect of isoflavones can either block or amplify the action of natural estrogens in the body.

Decades of scattered research into phytoestrogens has blossomed in recent years. Though studies of phytoestrogens are not nearly so extensive and comprehensive as those for hormone replacements produced by drug companies, they have sparked popular interest in dietary alternatives to hormonal drugs and the publication of several cookbooks featuring soy products and another source of an estrogen mimic, flaxseed.

The dietary approach appeals to many women who seek a ''natural'' alternative to hormones, especially since estrogen drugs have been linked to an increased risk of breast cancer, the disease women fear most. Isoflavones are believed to protect against that disease in a manner similar to tamoxifen, although definitive studies to demonstrate such protection have not yet been done.

Men, too, have begun to look to phytoestrogens for possible health benefits, including protection against heart disease and prostate cancer.

Caution Is Advisable

Before menopausal women abandon the drug approach for a diet rich in soybeans and flaxseed, it would be wise to consider the evidence for the effectiveness of phytoestrogens as well as their possible negative effects. To gain anywhere near the known benefits of hormonal drugs through food requires a fervent commitment to a near-vegetarian diet that is rich in foods not common to American tables or palates. While other beans, including lentils, kidney beans and lima beans, contain isoflavones, they are present in far larger amounts in soybeans.

To gain the benefits indicated by studies of phytoestrogens in menopausal women, it may be necessary to consume as much as a cup of soy protein powder (or its equivalent in other soy products) a day. Furthermore, the isoflavone content of soy products and other beans can vary widely depending upon how they were grown and processed. Without a laboratory analysis of each product, it is not possible to know how much of these chemicals may be in a particular food.

Keep in mind, too, that while hormone drugs have been tested for decades for safety and effectiveness in tens of thousands of women, what is known about plant-based estrogens comes largely from studies in laboratory animals and small groups of women tested for only weeks or months.


Weak estrogens do not have the same actions as the strong hormones that the body produces. This can be a benefit or a detriment, depending upon the hormonal status of the woman and the tissues being considered. Thus, in a premenopausal woman who produces an ample supply of estrogen, phytoestrogens can suppress estrogen and progesterone production and interfere with natural estrogen activity in some tissues, especially the breast and uterus. While such inhibition may reduce a woman's lifetime risk of developing cancer of the breast and endometrium, it may also cause infertility by interfering with ovulation or implantation.

In a woman past menopause, however, weak phytoestrogens may supply just enough of an estrogenic effect to reduce the frequency and severity of hot flushes, vaginal dryness, mood swings and other common menopausal symptoms, while still protecting the breast and uterus from undue estrogenic stimulation.

Dr. Claude L. Hughes Jr., an obstetrician-gynecologist and researcher into environmental and dietary estrogens at Duke University and Durham Regional Medical Center, emphasized that just because plant hormones are natural does not necessarily mean they are safe. ''Cobra venom, arsenic and cyanide are natural, but personally I avoid them,'' he remarked.

What Is Known

As for health benefits, Dr. Hughes said, ''there is suggestive epidemiology and some supportive animal studies, but there are still no long-term human clinical trials.'' What do these studies show?

Studies at Bowman-Gray University in Winston-Salem, N.C., among women entering menopause showed that eight ounces of a soy beverage a day diminished the number and severity of hot flushes and night sweats, but did not necessarily eliminate them. Dr. Hughes pointed out that Japanese women do have menopausal symptoms -- they call it ''tight shoulders'' -- but they are less severe and less often reported to physicians.

Studies in monkeys and a few small studies in women have indicated cardiovascular benefits: a decrease in harmful LDL cholesterol without lowering beneficial HDL cholesterol, greater flexibility of arteries and a reduced risk of clogged arteries. Rodent studies indicate that the isoflavone genistein (formed in the body when soy is consumed) can block the growth-stimulating effects of estrogen in the breast and endometrium, but it is not yet known if this also occurs in women.

The data on bone loss are conflicting. One study at the University of Illinois indicated a significant increase in spinal bone density in postmenopausal women consuming soy products, but other studies have not shown a benefit to bones. And there is as yet no evidence that phytoestrogens benefit the brain, Dr. Hughes said.

Also worth considering are the digestive effects of soy and other beans. Unless these are gradually introduced to one's diet, they can cause serious intestinal gas and discomfort, and some people have a food intolerance to soy and are unable to digest it at all. Dr. Hughes suggested gradually building up to a daily intake of 30 to 50 milligrams of isoflavones, the amount consumed by the average Japanese woman. The accompanying chart may be used as a guide.

But he warned against taking genistein capsules sold in health food stores, saying, ''There is little quality control and the consumer has no way to know if they contain what the label says or whether the recommended doses are safe.''

Chart: ''AT A GLANCE: Plant Foods That Affect Hormones'' Phytoestrogens, plant materials like isoflavones with estrogen-like activity, are most plentiful in foods derived from soybeans. Total phytoestrogens (in milligrams Food per 3.5 ounces) Roasted soybeans 162.5 Textured vegetable protein 138.2 Green soybeans 135.4 Soy flour 112.4 Tempeh 62.5 Tofu 33.7 Tofu yogurt 16.4 Soy hot dog 15.0 Soy noodles (dry) 8.5 (Source: Obstetrics & Gynecology)