Nutrition Action Healthletter
Jan/Feb 2000 — U.S. Edition 

Practicing Safe Soy

 Are phytoestrogen powders and pills safe to take?

   “We don’t know,” says soy researcher Gregory Burke of Wake Forest University. “We don’t have evidence suggesting they’re not safe. But I’m concerned that it’s easier for people who take pills to get larger dosages, which may put them at higher risk.”

   Two recent studies have also raised red flags. British researchers last year found that eating

about two ounces of soy powder containing 45 mg of isoflavones each day for just two weeks stimulated the proliferation of epithelial breast cells in premenopausal women.1 An earlier U.S. study found an increase in breast cell proliferation in more than a quarter of women given a daily soy protein beverage with 38 mg of isoflavones.2

   Any time cells multiply, there’s an increased risk of cancer. “That’s very worrisome,” says Tufts University researcher Margo Woods. “If we had no data suggesting harm, I’d feel a little bit better. But this is in the opposite direction of what we expected.”

   Animal evidence also raises questions. “If lab mice are fed the isoflavone genistein before they’re exposed to a cancer-causing chemical,” says Bill Helferich of the University of Illinois at Urbana-Champaign,“the development of breast cancer is suppressed. In some studies, if they get the genistein after cancer has begun to develop, the genistein stimulates the growth of tumors.” Researchers don’t know if the same is true in humans, he cautions.

   But until they find out, anyone who has had breast cancer should stick to soy foods (like tofu), not supplement pills or powders.


1: Amer. J. Clin. Nutr. 68 (6 Suppl): 1431S, 1998.
2: Cancer Epidem. Bio. Prev. 5: 785, 1996.

   Yes, they know that estrogen curbs hot flashes, night sweats, vaginal dryness, mood swings, changes in sleep patterns, and other symptoms of menopause.

   They may also know that, over the long term, hormone replacement therapy reduces the risk of heart disease, osteoporosis, and maybe even Alzheimer’s disease.

   But for many, estrogen simply isn’t an option as long as some research suggests that it may raise the risk of breast cancer.

   Can you smell an opportunity?

   Supplement makers can. “Dramatic benefits within 4 to 8 weeks,” promises Remifemin. A midlife change “just as Nature intended,” offers Promensil.

   Of course, it doesn’t hurt sales that taking anything seems to help relieve menopausal symptoms, at least for a time. “The placebo effect is giant,” concedes one manufacturer.

   But beyond that, there isn’t much evidence that menopausal shakes, powders, or pills work.

Heal, Phyto!
The active ingredients in most dietary supplements for menopause are phytoestrogens — chemicals found in plants that may act like the estrogen produced naturally in the body.

“These plant estrogens are thousands of times weaker than natural estrogen,” says nutritionist Mindy Kurzer of the University of Minnesota. “But they also circulate in the blood at levels thousands of times higher than natural estrogen.” That’s why researchers want to know if plant estrogens work like natural estrogen.

   The food that is richest by far in phytoestrogens is soybeans. A typical three-ounce serving of tofu, for example, contains about 23 milligrams of isoflavones (the major group of phytoestrogens). About a half-cup of shelled peanuts, on the other hand, has less than a tenth of a milligram. Menopausal supplements made from herbs like black cohosh, red clover, and dong quai may contain soy-like levels of plant estrogens.

   “A Japanese person who eats a traditional fish, rice, and soy-based diet probably consumes an average of 20 to 40 mg of isoflavones a day from soybeans,” says soy expert Mark Messina of Nutrition Matters, a consulting firm in Port Townsend, Washington. People in the Western industrialized countries, on the other hand, get only about five milligrams a day from their food.

   “Researchers thought that Asian women may experience milder symptoms during menopause than Western women because the soy foods in their diets provide plant estrogens to supplement their dwindling supply of natural estrogen,” says Margo Woods of Tufts University in Boston.

   But that’s not proof that soy foods — or the phytoestrogens in soy foods or menopausal supplements — ease women’s discomfort. Here’s the evidence on soy powders and foods made from soy.

Soy Foods and Powders
So far, seven studies have compared soy protein shakes, bars, muffins, and flour to look-alike (but soy-less) placebos. Two of them found that soy curbed hot flashes. But even though both studies used similar soy powders, their results were inconsistent:

Once a day for six weeks, Gregory Burke and colleagues at Wake Forest University in North Carolina gave a soy protein beverage containing 34 mg of isoflavones to 42 women who had been experiencing at least one daily hot flash or episode of night sweats.1 For another six weeks the women were given a placebo beverage, and for another six weeks they were given the soy beverage twice a day.

   Drinking soy once a day did nothing to relieve their symptoms, the women reported, while taking it twice a day reduced the severity — but not the number — of hot flashes by 20 percent. The soy drinks had no effect on other symptoms.

In an Italian study, 51 women with severe hot flashes drank a soy protein beverage twice a day (with a total of 76 mg of isoflavones) for 12 weeks, while 54 similar women were given a placebo beverage.2

   The average number of hot flashes in the soy-drinkers declined from 11 a day to six. In the placebo group it dropped from 11 to eight. While statistically significant, “that’s a very modest difference,” says Tufts’ Margo Woods. “It may not be enough for some women who are looking for an alternative to estrogen.”

   The Italian researchers didn’t measure the severity of the women’s hot flashes, and the soy had no effect on symptoms like anxiety, headaches, or insomnia.

   (The beverages used in the U.S. and Italian studies were similar to Ross Laboratories Health Source Soy Protein Shake.)

   In five other studies, soy products were no better than soy-free placebos at relieving any menopausal symptoms. They included:

soy-flour muffins (with 80 mg of isoflavones) eaten once a day by 48 women for six months,

soy bars (with 23 mg of isoflavones) eaten twice a day by 76 women for three months, and

bread baked with soy flour (with 70 mg of isoflavones) eaten once a day by 23 women for 12 weeks.3

   Three of the five studies haven’t been published yet.

   The bottom line: “Most studies find that soy has no effect on menopausal symptoms,” says Burke. “When a benefit is detected, it appears to be relatively mild, and much less than what women get from estrogen replacement therapy.”

   No good studies have looked at foods like tofu, soy cheese, or soy burgers (some burgers and other soy foods may not even have decent levels of isoflavones). As for menopausal supplement pills: “We have yet to see any good published data that suggest that these pills have a significant impact on menopausal symptoms like hot flashes or night sweats,” says Burke (see p. 10). What’s more, generous doses of isoflavones — from powders or pills — may not be safe (see “Practicing Safe Soy”).

   “Soy will probably lower your cholesterol levels if they’re high, and maybe future research will show that soy can prevent osteoporosis and certain cancers,” says Burke.

   But when it comes to the discomfort of menopause, don’t expect a miracle.

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1: Menopause 6: 7, 1999.
2: Obstet. Gynecol. 91: 6, 1998.
3: Climacteric 1: 124, 1998.

See Also: The Soy Story

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