Going Soy Crazy

By Sora Song

It can't sprout a beanstalk into the heavens, but if even half the claims being made in behalf of the 5,000-year-old soybean are true, it may be the closest thing on earth to a magic bean. Not only is soy a low-fat food, but it's also believed to fight cancer, lower cholesterol, relieve hot flashes, boost bone density, brighten skin and even soften beards. Though none of these claims have yet been proved, manufacturers are riding high on the soy-is-healthy wave and pumping the marketplace full of soy products--some 300 new ones hit grocery-store shelves just last year. In all, more than 3,000 products are now available--and consumers are hungrily snapping them up.

So is soy really as beneficial as people think? Researchers have focused on one particular group of compounds in soy: the isoflavones, which are also found in lower concentrations in other legumes. Isoflavones are phytoestrogens, or plant estrogens, that weakly imitate the body's estrogen--sometimes they have an estrogenic effect, other times anti-estrogenic. They are thought to help stave off breast cancer, lower cholesterol and reduce the risk of heart disease, among other things. Just last month a study in the Journal of the National Cancer Institute suggested that isoflavones may also reduce the risk of endometrial cancer.

Support for the idea that soy products protect against breast cancer comes mainly from epidemiological studies in Asia, where people have routinely been eating soy for thousands of years and where women have markedly lower rates of breast cancer than in the U.S. But whether that's due to soy remains uncertain. "The cultures are just so different in so many ways, in diet and other lifestyle factors," says Mark Messina, a Port Townsend, Wash., nutritionist and an expert on soy. "By itself, the low breast-cancer rate in Asia doesn't provide much insight into the possible effect of soy on breast-cancer risk."

Meanwhile, lab studies on rats have alternately suggested that isoflavones inhibit and stimulate breast-cancer tumor growth. Recent studies showing that estrogen in hormone replacement therapy actually increases the risk of breast cancer and heart disease in postmenopausal women have scared some women off soy.

"I think eating soy foods--tofu, soy milk or miso--in moderation, a couple of times a week, should be fine. That's the advice I would take if I had breast cancer or were at risk," says Anna Wu, professor of preventive medicine at the University of Southern California's Keck School of Medicine. On the other hand, Wu doesn't recommend taking soy in pill form or as a protein powder. "We have no data on that. I would not take it as a supplement," she says.

The most uncontested research suggests that soy is a good way to combat high cholesterol. The key, say nutritionists, is to eat soy as part of an overall heart-healthy diet. A study published last month in the Journal of the American Medical Association showed that people with high cholesterol who ate a special vegetarian diet high in fiber and rich in foods known to lower cholesterol--such as soy, oats and almonds--reduced their cholesterol levels by 29%. That was almost as big as the 31% drop for subjects in a group that was given a simple low-fat vegetarian diet along with the drug lovastatin.

It may be some time before scientists can figure out whether soy lives up to its magical claims, but nutrition experts fully support adding soy to the average American diet--especially if it replaces something less healthful. For instance, consumers would do well to replace regular milk with fortified soy milk. "If it turns out that soy doesn't reduce breast cancer, for example, it's still a good source of protein that's low in saturated fat and cholesterol," says Messina. "To me, it's a complete no-brainer."