Date: Sun, 11 Feb 2001 17:56:53 +0100 From: info <[EMAIL PROTECTED]> ----- forwarded message ----- Subject: [MLNews!*] Experts Concerned About Soy and Breast Cancer (Washington Post) Date: Sat, 10 Feb 2001 21:40:53 EST From: [EMAIL PROTECTED] Experts Concerned About Soy and Breast Cancer While the U.S. Food and Drug Administration (FDA) allows food labels to display a health claim stating that soy products can lower blood cholesterol, the amount of soy foods necessary to achieve this benefit -- as many as four servings a day -- comes awfully close to the level that some researchers say might increase the risk for developing breast cancer. That's right: Some scientists are concerned that too much soy could promote the growth of malignant tumors rather than protect against them. "Most of the women who are taking large amounts of soy, my impression is that they're doing it to avoid breast cancer," says Regina Ziegler, an epidemiologist with the National Cancer Institute (NCI). "But there's a dearth of information about different levels of soy on the risk for breast cancer. I don't want to scare people away from it, but as a scientist I can't say what levels are safe or unsafe." Mark Messina, a soy industry promoter, agrees. "It's basically an unresolved issue," says Messina, a soy expert who serves as an adjunct associate professor of nutrition at Loma Linda University in California. It is clear, he comments, that soy contains estrogen-like compounds, so if you have the type of breast cancer that depends on estrogen to develop and progress, "you have to think about whether you want to run out and start eating three servings of soy a day." Adds Barry Goldin, who has researched soy at Tufts University Medical School in Boston, "Whenever you mention estrogen, you're talking about concern. Estrogen is a double-edged sword." Estrogen in Plants and Elsewhere The plant estrogens, or phytoestrogens, in soy are known as isoflavones. In the 1980s, investigators found that feeding soy to rats reduced their incidence of mammary tumors. More important, when the scientists removed the isoflavones from soy and again fed it to rats, the soy no longer suppressed tumor growth, further suggesting anti-cancer properties. The mechanism by which isoflavones are thought to block tumor production works as follows. Breast cells contain estrogen receptors, which enable them to "recognize" estrogen and take it up into breast tissue. But some common types of breast cancer essentially feed off estrogen, so the goal is to keep estrogen out. That's where isoflavones of the sort found in soy products come in. These weak plant estrogens are close enough in structure to human estrogen that breast receptors mistake them as such and allow them in, which in effect blocks the entry of harmful human estrogen. Epidemiologic evidence supports the theory. Women throughout Asia, who for centuries have eaten much more tofu and other soy products than Americans, are much less likely to develop breast cancer than American women. Word about the cancer-fighting value of soy estrogens has certainly gotten out, no doubt contributing to the hundreds of millions of dollars in sales of soy products annually. Women are buying not just tofu but also soy milk, soy-laced energy bars, soy cheese, soy ice cream and soy-based meat analogues meant to resemble turkey, chicken, hamburger and bologna. Then there are the soy-based powders to mix into smoothies and such, as well as soy supplements -- little pills with high concentrations of isoflavones. But there's a soy snafu, with emerging science presenting a less certain picture of soy's benefits. In one study, women who were given soy supplements experienced increased proliferation of breast cells, at least initially. That's a potential problem because the more breast cells proliferate, the greater the chance of a mutation that could give rise to cancerous cells that would quickly grow into a tumor. In animal research, human breast cancers transplanted to mice were helped along when the mice were fed various dosages of soy isoflavones. In other words, soy appeared to work in concert with human estrogen rather than against it. The scientists major concern is about isoflavone intake. I think healthy people should not consume more than 100 milligrams of isoflavones per day," says Loma Linda's Messina. There's no historical precedent for consuming more," he says out. "One hundred milligrams is like three servings a day, and maybe 5 to 10 percent of the Japanese population consumes that much." Most have one serving of soy food daily. "I can't point to data showing that 100 milligrams is dangerous," Messina stresses. It's not like if you take 100 milligrams of isoflavones and then you take 101, you're risking your life. But the 100 milligram-limit is consistent with a healthy, plant-based diet." Goldin has arrived independently at same recommendation. "If a person wanted tofu mixed into her stir-fried vegetables once or twice a day, I would not see any problems with it at all." Goldin is also comfortable with a woman at high risk for breast cancer having three to four ounces of tofu two to three times a week. "But I would not take 100 milligrams of isoflavones a day," he says, meaning he would not eat more than a couple of servings of soy-containing foods daily -- and would be very careful about choosing a soy powder or supplement, some of which contain quite high levels of isoflavones. Ziegler, like the others, supports modest servings of soy-based foods but also throws up a red flag for powders and pills. "I'm not concerned about soy intake comparable to what we see in Asian communities," she says. "Even if a woman already has breast cancer, I don't think she needs to worry about going into a Chinese restaurant and having a tofu dish." Indeed, women in Asia with breast cancer, who don't stop eating soy foods once they are diagnosed, have better prognoses than American women with the disease. "On the other hand," says Ziegler, "given the supplements, we're going beyond what one would see in a typical Asian diet. We don't know how that plays into a woman's health. I don't think we can say that pharmacologic levels of soy are useful in avoiding breast cancer." Margo Woods, a breast cancer researcher in the Department of Family Medicine and Community Health at Tufts University Medical School, says she is particularly concerned about high levels of isoflavones for women taking tamoxifen. The drug tamoxifen, like the isoflavones in soy, is an estrogen-like compound that keeps human estrogen out of breast tissue. And some women who have breast cancer or are at very high risk are given the drug to slow down cancer progression or development. But the isoflavones in soy could compete with tamoxifen for uptake by breast tissue, Woods says. "Once a woman is on tamoxifen, my position is that it's not wise to interfere," she says. That is, concentrated isoflavones in certain soy products may have the potential to reduce the drug's effect. For others, Woods doesn't endorse an upper limit of 100 milligrams of isoflavones a day. "I feel most comfortable with a range of 35 to 55 milligrams," she notes. That's about two to three ounces of tofu a day. "People shouldn't be thinking of soy as a medicine," she says. Including it as "part of a fruits, vegetables and whole grains package is a wise thing to do. The population that has been eating that way for years is at lower risk". But soy is not a miracle treatment People think a food is going to be like penicillin. It's not. Ziegler sees it the same way. "We should get away from soy as a cancer preventer," she says. "Maintaining an ideal weight, that will definitely reduce the risk. And it can be achieved by a diet that's high in fruits, vegetables, grains and legumes. Soy is one type of legume, but it's not the answer. The Washington Post Tuesday, January 30, 2001; Page HE08,9
