Epidemiologists hope a new study on soy may help clarify the bad, the good, and the ugly about one of America's top nutritional supplements.

First, the obvious: women are confused. The data on soy-what it does and what it does not do-presents a very complicated picture.

"There are plenty of women out there who are already eating a lot of soy on a regular basis, and we just don't have enough science behind us yet to tell them if that's a good thing or not," says Dr. Electra Paskett, an expert in cancer control at The Ohio State University Comprehensive Cancer Center.

Paskett, as chair of the cancer control and health outcomes committees of one of the country's largest cancer trial groups, the Cancer and Leukemia Group B (CALGB), has a special interest in soy research because she herself is not only a scientist, but also a breast cancer survivor.

As part of her position with the CALGB, Paskett oversees a number of trials in clinics and centers all over the United States that are assessing the impact of soy on postmenopausal breast cancer patients who are taking tamoxifen.

Tamoxifen has been shown to be effective in preventing breast cancer recurrence, but one of its side effects is hot flashes. Hot flashes are also problematic for women who go through early menopause induced by chemotherapy.

Some studies suggest adding soy to the diet is a good way to ease hot flashes, but Paskett says "the jury is still out."

Soy contains substances called phytoestrogens, plant-based hormones that can mimic naturally occurring estrogen in the body.

Postmenopausal women who have a history of breast cancer or who are at high risk of developing breast cancer are typically not advised to take estrogen as part of any hormone replacement therapy (HRT) because some studies show estrogen might increase cell proliferation. So many women turn to soy, a plant hormone that weakly mimics estrogen, hoping it will somehow produce the same benefits as estrogen, but with none of its possible consequences.

"But we don't really know how much soy is OK to take," says Paskett.

Paskett says interest in soy comes from observation of Asian women, who typically consume large amounts of soy in their diets. Asian women have a much lower rate of breast cancer, but when they move to the United States, their risk and incidence of breast cancer matches that found in the U.S. "So it sure looks like soy might confer some sort of protection and might inhibit the growth of cancer," says Paskett. But she also points out that Asian women eat substantial amounts of soy beginning in childhood, and that means "we really don't know what a sudden jump in soy intake would do to someone who doesn't typically eat that much."

In addition, some studies show that soy supplements actually may stimulate cell growth, not inhibit it.

These apparently contradictory effects might both be true, because phytoestrogens like soy mimic estrogen in some tissues, but not others. In other words, their activity is tissue-dependent.

So what's a woman to do?

The current study opening in CALGB centers across the U.S. will randomize women into two study groups. Participants in one group will add about 60 mg of soy with isolflavones to their diets daily-a typical amount found in the Asian diet-for three months; the other will take casein protein without soy isolfavone for the same period. Researchers will measure the number and intensity of the hot flashes the women experience.

Paskett says earlier studies suggesting soy has little or no effect upon hot flashes have simply examined soy's active ingredient, genistein, as a diet supplement in pill form. She says the new round of studies will be different. "We think it is important to use the whole soy food, because it may be the synergistic properties of various elements in the food that may be beneficial-not just one ingredient."

Right now, Paskett says, "The only thing we can tell women who need help with hot flashes is to exercise regularly and take vitamin E. We may eventually be able to say something definitively about soy, but not yet."

SOURCE:
Ohio State University Medical Center (http://www.osumedcenter.edu)