Does Soy Curb Hot Flashes?

Maybe, but Look for Relief From Food, Not the 'Active Ingredient,' Suggests Study

April 24, 2003 -- Women not taking hormone replacement therapy are often advised to eat soy-rich foods such as tofu to help reduce menopausal symptoms such as hot flashes, flushing, and night sweats because they contain high levels of isoflavones, a substance that mimics estrogen.

For every gram of soy food consumed, you get 2 milligrams of isoflavones, a type of plant estrogen that behaves as a weaker form of the body's estrogen. So, the theory goes, the more soy consumed -- and in particular, the more isoflavones -- the less likely women who are experiencing menopause will be bothered by its symptoms. Case in point: Japanese women who consume soy-rich diets traditionally have much lower rates of rates of menopausal problems.

Yet scores of studies on the relief produced have shown mixed results: Some show a modest benefit in symptoms among women consuming high amounts of isoflavones-rich supplements and foods, while others show no benefit at all. The latest study to investigate their benefits in menopause -- among the longest and most comprehensive trials ever done -- may provide some explanation to the mixed results.

Researchers say that it appears as though soy protein itself may be beneficial, but not the much-ballyhooed isoflavones in them. In other words, it's soy foods themselves that may bring relief, but not their long-considered active ingredient. In fact, in their study, menopausal women getting the least amount of isoflavones enjoyed slightly more relief in the number and severity in symptoms.

"We were looking at the data and were truly amazed," says researcher Mara Z. Vitolins, DrPH, MPH, RD, of Wake Forest University School of Medicine. "The take-home message of our finding is that dosing with isoflavones doesn't seem to be the way to go."

In her study, published in the current issue of Menopause, 241 women between ages 45 and 55 were divided into three groups. The "controls" consumed 25 grams of soy protein each day for two years but received no additional isoflavones supplements -- in fact, they also were taking a substance to wash away all but a scant 4 milligrams of isoflavones. Two other groups also got the soy protein drink, but with no depleting wash, along with either a 42 milligram or a 58-milligram isoflavones supplement daily. Yet the controls experienced the most dramatic relief in self-reported diaries and physical exams.

Though all of the patients reported fewer and milder events of hot flashes, flushing, and night sweats, the researchers believe it was due to the soy protein itself -- if not a placebo effect.

"It looks as though the 'whole' food may be effective, but not the isoflavones," Vitolins tells WebMD. "There appears to be some sort of synergy that goes on with the protein -- the whole mix in the food is where you may get the benefit. Maybe the protein or other substances act as a carrier of these molecules that seem to reduce symptoms. But the isoflavones found in supplements themselves don't offer benefit, judging by our study."

Her advice: Continue to eat soy-rich foods, which have also been shown in some studies to help lower cholesterol, increase bone density, and possibly protect against some forms of cancer. But don't rely on supplements.

"This is so important for women to know, because they're going out and buying these isoflavones supplements, believing they help," says Vitolins. "Unfortunately, with protein comes fat, and many women are dieting and therefore don't get enough protein of any type, including soy protein. But it's so important to their overall nutrition. If you look at the Japanese, who have very low rates of menopause symptoms and other health conditions, they're eating soy protein in foods. They don't take supplements."

And the way they eat the soy may provide another clue to their better health. "The benefit in soy might be from consuming it in varying amounts," she tells WebMD. "Estrogen receptors seem more primed when they are hit with soy protein, then don't get a lot, and are then hit again. Japanese women aren't counting their soy intake or the number of isoflavones they consume. Perhaps the best route might be to consume soy in varying amounts, rather than try to consume a continuously high amount every day."

Others studies seem to suggest that more isn't necessarily better -- at least when it comes to soy and its reporting beneficial compounds. In a study last year, researchers at the University of Illinois at Chicago found there was no difference in levels of key sex hormones in the blood -- believed to bring relief from menopausal symptoms -- among women who took varying levels of a soy supplement, even at doses higher than those used in Vitolin's research.

"This is an intriguing piece of evidence, especially since it's a longer study than most, which is very useful. But menopausal symptoms happen quickly and typically subside over time," the lead researcher of that study, Victoria Persky, MD, tells WebMD. "This study indicates that isoflavones supplements are not necessarily beneficial, and we need more evidence."

Show Sources

SOURCES: Menopause, March-April, 2003. American Journal of Clinical Nutrition, January 2002. Mara Z. Vitolins, DrPH, MPH, RD, assistant professor of epidemiology, Wake Forest University School of Medicine, Winston-Salem, N.C. Victoria W. Persky, MD, professor of epidemiology, University of Illinois at Chicago School of Public Health.
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