Many soy food products carry health claims stating that they reduce the risk of heart disease. A review of the evidence, however, suggests that soy's cardiovascular benefits may have been overestimated by the early studies that formed the basis for its health claim.
According to the Nutrition Committee of the American Heart Association (AHA), recent clinical trials have failed to confirm that soy protein has clinically important favorable effects on cardiovascular health. Committee Chair Alice H. Lichtenstein, DSc, who is also Stanley N. Gershoff Professor of Nutrition Science and Policy at the Friedman School of Nutrition Science and Policy at Tufts University, co-authored the updated scientific advisory report just published in Circulation.
"A very large amount of soy protein, more than half the daily protein intake, may lower [bad] LDL cholesterol by a few percentage points when it replaces dairy protein or a mixture of animal proteins. However, this is not the normal level that people in this country consume. The evidence is less favorable for soy isoflavones as the responsible component," said Lichtenstein. In addition, "no benefit is evident on [good] HDL cholesterol, triglycerides, lipoprotein(a), or blood pressure."
"The efficacy and safety of soy isoflavones for preventing or treating cancer of the breast, endometrium, and prostate are not established; evidence from clinical trials is meager and cautionary with regard to a possible adverse effect. For this reason, use of isoflavone supplements in food or pills is not recommended," the authors say.
"Soy products such as fresh or frozen soybeans (edamame), tofu, soy butter, soy nuts, and some soy burgers should be beneficial to heart health when they displace foods such as hamburgers, cheese and other sources of saturated fat from the diet," says Lichtenstein. "Heart disease is a major problem - using soy protein instead of animal protein is still a win." Lichtenstein is the director of the Cardiovascular Nutrition Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts.
The Nutrition Committee of the AHA assessed the results of 22 studies on soy protein and its component isoflavones. Although reduction in LDL cholesterol was previously believed to be most responsible for soy's cardiovascular benefits, the overall effect observed in this analysis was an average reduction of only 3 percent. "Yes, it's a reduction," says Lichtenstein. "But that is after consistently high intakes and it is not as high as we once thought it to be." Lichtenstein and colleagues point out that this remains a dynamic area for research, and that the "AHA will continue to monitor the results and modify its advisory statement as needed."