The Truth About Soy

By Susan Learner Barr, M.S., R.D.

(it's not what you think)

Once touted as a miracle food, soy has morphed from a vegan staple to a mainstream meal ingredient over the past three decades. Ever since 1999, when the FDA first allowed soy products to claim on their packaging that they decreased cholesterol and the risk of heart disease, sales have skyrocketed. Americans started swapping meat for tofu and adding soy-protein powder to smoothies, spurring a $4 billion-a-year business. But recently a backlash has kicked in, as numerous studies paint a less-than-rosy picture of soy and its reputation as a healthy deterrent of breast cancer, osteoporosis, and other diseases. The American Heart Association (AHA) has also changed its position on soy, concluding in a recent report that it doesn't lower LDL (bad) cholesterol as much as experts had thought.

So just what are the health perks of this legume? "Soy is a low fat protein that's beneficial in a balanced diet," says Leena Hilakivi-Clarke, Ph.D., a Georgetown University professor who has studied the link between soy and breast cancer. "Many condition-specific claims, however, seem to be inflated, misinterpreted, or just not based on sound scientific studies." Here, Shape sets the record straight about the real benefits of eating soy.

The claim: Soy prevents heart disease

What you need to know : According to a recent study from Johns Hopkins University, soy appears to play a role in lowering cholesterol in postmenopausal women. By mimicking the hormone estrogen, isoflavones (plant compounds in soy that act like weak forms of the hormone) may prevent cholesterol levels from rising in postmenopausal women. But young women produce estrogen on their own, so additional benefits from soy would likely be minimal. The explanation: "Estrogen keeps cholesterol levels steady; cholesterol tends to increase after women enter menopause and no longer make this hormone," says study author Jerilyn K. Allen, Sc.D., an associate dean for research at Johns Hopkins University School of Nursing.

The bottom line: Just because your cholesterol levels won't plummet from eating soy doesn't mean it won't help your heart. "Soy is a good alternative to meat because it's lower in cholesterol-raising saturated fat," says Alice H. Lichtenstein, D.Sc., a professor of nutrition science at Tufts University. Use soy-based meat substitutes in lasagna or tofu in stir-fries occasionally, and try tofu as a replacement for cheese (also high in saturated fat).

The claim: Soy protects your bones

What you need to know: Don't count on tofu and tempeh to strengthen your skeleton. Research in the Journal of the American College of Nutrition (one of the only studies among premenopausal women) revealed that women in their early 20s who took soy isoflavone supplements for one year didn't experience any more of an increase in bone density than a group who didn't take them. Results for older women are more promising but still mixed. The AHA report found that isoflavones reduced bone loss in some research but not in others. "Estrogen helps spur the growth of certain bone cells, so isoflavones may have a greater bone-building effect on women who no longer produce the hormone," says John J.B. Anderson, Ph.D., a professor of nutrition at the University of North Carolina-Chapel Hill. And though a study from the Archives of Internal Medicine found that postmenopausal Chinese women who ate the most soy foods were nearly 40 percent less likely to suffer broken bones than those who ate the least, scientists caution that more research is needed to conclude that eating soy alone caused the reduction in risk.