Help for Hot Flashes

Is soy the solution to this menopausal symptom?

Medically Reviewed by Brunilda Nazario, MD
6 min read

Soy once was relegated to an obscure corner of most supermarkets, if it was there at all. In most communities, if you really wanted to take a taste of tofu or other soy products, you had to venture instead into a health-food store, searching for soy somewhere between the bean sprouts and the herbal remedies.

But these days, the soy fad has gone mainstream. Faster than you can say tempeh or edamame, more Americans than ever have become convinced that there might be some substance to the 5,000 years of Asian reliance on the simple soybean and the foods derived from it. Moreover, particularly as many menopausal women have become concerned about the safety of using prescription hormone replacement therapy (HRT) to cool down their hot flashes and related symptoms, soy just might be a sensible alternative worth trying.

The simplest definition of menopause is "the end of menstruation." When women reach menopause, about 25% feel no different, except that their periods stop. But for the remainder, at times they may feel like a 9.5 quake has jolted their body to its core, providing an inescapable reminder that they're not as young as they used to be. Hot flashes. Night sweats. Sleep disruptions. Vaginal dryness. Mood swings.

More than any other symptom, however, it's those scorching hot flashes that sabotage the sense of well-being, affecting as many as 85% of menopausal women to one degree or another. And while HRT once was seen as the best hope for dousing those hot flashes, a major new study -- the Women's Health Initiative (WHI) -- has sent a chill down the spines of many health-conscious women and their doctors. In July 2002, WHI researchers reported that long-term use of the most commonly used hormone replacement preparation of estrogen and progestin, Prempro, could increase a woman's risk of heart disease, stroke, and invasive breast cancer.

More recently, the second arm of that same study, in which women who had hysterectomies received estrogen only (Premarin) -- was stopped one year ahead of schedule.

The main goal of this study was also to see if starting menopausal hormone therapy might lower a woman's risk of heart disease. It did not. In the estrogen-only group, there was no increase or decrease in heart disease. However, women taking estrogen-only hormone therapy had a slightly increased risk of stroke, a risk similar to that seen in the estrogen and progestin study.

As a result, the search for a non-drug approach to managing menopausal symptoms has accelerated, with many women looking toward soy for deliverance from the raging heat within. And, in fact, they're finding many soy products that are being marketed as nutritional fire extinguishers.

In Asian countries where soy is a dietary staple, women tend to get fewer hot flashes than women in the U.S. But when studies have looked closely at soy's effects on menopausal symptoms, the results have been mixed.

"I'm a strong proponent of soy, and think that menopausal women should be incorporating soy into their diet," says Mark Messina, PhD, MS, an adjunct professor of nutrition at Loma Linda University in Loma Linda, Calif. "But I'm not basing that recommendation solely on its effects on hot flashes."

One of the studies most strongly supporting soy foods, says Messina, was research from Italy published in 1998, which found a 45% reduction in hot flashes in women consuming soy protein, compared to a 30% improvement in the placebo group. But for every positive study, he adds, there has been another showing no soy-related benefits.

In research published in March 2002 in the journal Obstetrics & Gynecology, menopausal women took a daily dose of 100 mg of soy isoflavones (an estrogen-like constituent of soy that appears to be the key ingredient easing hot flashes). These women experienced a significant decline in their menopausal symptoms, including hot flashes, mood swings, and sleep difficulties. But in another study in 2002 at Tufts University, researchers found that after three months of soy supplementation, women had no more relief from hot flashes than another group taking a placebo (dummy) pill.

In the heat of the debate, doctors like Machelle Seibel, MD, remain persuaded by the positive findings, and urge women to give soy a try. "There is some good data that soy can reduce both the frequency and the intensity of hot flashes by about 50%," says Seibel, professor of clinical obstetrics and gynecology at the University of Massachusetts Medical School in Worcester. "A lot of doctors feel that somehow that's not significant enough, and would prefer that it eliminate all hot flashes. But if it can reduce hot flashes sufficiently enough so a woman can get a good night's sleep, that may allow her to cope better."

Mary Hardy, MD, medical director of the Integrative Medicine Program at Cedars-Sinai Medical Center in Los Angeles, believes that even the positive findings for soy in some studies have shown only a modest impact on menopausal symptoms. At the same time, she says, "some individual women say that soy has had a tremendous effect on managing their hot flashes. However, I wonder if it's the soy per se, or did these women also reduce the fat in their diet, or restrict their caffeine or alcohol intake? But as part of moving to an overall healthier diet, I think that soy can be an important component of those changes."

While Messina tells women that soy may have a modest benefit on menopausal symptoms, he says, "it's not the most important reason to take soy. I think the heart benefits and the possible bone-strengthening benefits of soy foods are more important reasons." For example, the evidence indicating that soy can reduce blood cholesterol levels is so strong that the FDA permits this claim on food labels.

If you want to give soy a try, most experts suggest consuming one to two servings per day, which translates to an intake of about 25 to 50 mg. of isoflavones. "If you don't experience any benefit from two servings of soy," advises Messina, "then you can try adding another one."

You'll find soy in foods such as tofu, soy milk, whole soybeans (like edamame), miso, soy yogurt, and tempeh -- although some women report that it takes a little time to develop a taste for soy.

"There are still people who are in the 'I-won't-eat-soy-and-you-can't-make-me' crowd," says Hardy. But many might be agreeable to eating soybeans, she says, even as a snack food, or drinking a shake prepared with soy powder, or adding "soy crumble" to sauces.

Soy supplements -- most containing 25 mg. of isoflavones per pill -- are available at health-food stores. "As a general rule, you're better off getting what you're looking for from foods rather than from tablets," says Seibel, author of The Soy Solution for Menopause: The Estrogen Alternative. "Even so, some of the studies showing benefits from soy in reducing hot flashes were conducted with pills containing isoflavones."

Messina agrees, noting that as a nutritionist, he always prefers food rather than pills. But he adds, "this is a country where most people don't eat any soy, so consuming even two servings can be a challenge for them. For that reason, I don't have a problem with someone saying, 'On the days that I don't eat two servings per day, I'll take a pill to bring my level up to the recommended amount.' But food is still best because hopefully the soy servings will take the place of less healthy foods in your diet. If you were eating soy nuts instead of potato chips, for example, that would be wonderful."