Soy is ineffective at lowering cholesterol, despite years of recommendations to the contrary, the American Heart Association says in a study currently published online in its journal Circulation.
The AHA reviewed 22 studies published since 2000 and found that on average, soy protein reduced LDL cholesterol by only 3 percent. In addition, the committee that reviewed the studies found that by themselves, soy isoflavones had no clinically significant impact on cholesterol. What's more, claims that soy can help ease symptoms of menopause or prevent cancers of the breast, uterus or prostate were baseless, the committee said, noting that in some cases, soy may have a possible adverse effect. Because of this, "use of isoflavone supplements in food or pills is not recommended," the report's authors wrote.
The AHA has recommended soy as part of a heart-healthy diet since 2000, a year after the U.S. Food and Drug Administration approved a heart-health claim for products with at least 25 grams of soy protein. In its new report, the committee stated, "The direct cardiovascular health benefit of soy protein or isoflavone supplements is minimal at best."
Andrew Shao, Ph.D., vice president, scientific and regulatory affairs with the Council for Responsible Nutrition, noted that soy is just one element of a heart-healthy lifestyle. "Folks need to remember that the benefits of soy protein for cardiovascular health are modest. They've always been modest—not what you would find using a statin drug, for example.… If [people] make other diet and lifestyle changes, it's probably preferred over using prescription drugs," he said.
However, the AHA committee also noted that soy protein does have a role in a healthy diet. "Soy products such as tofu, soy butter, soy nuts or some soy burgers should be beneficial to cardiovascular and overall health," especially when replacing animal protein or other sources of carbohydrates and fats, "because of [soy's] high content of polyunsaturated fats, fiber, vitamins and minerals, and low content of saturated fat."
Because the AHA reinforced soy's utility as a healthful source of protein, Shao thinks consumers won't necessarily stop eating it. Nor will the report sway the FDA, Shao suggested.
"[AHA] combined studies together. It's not quite proper—it's like mixing apples and oranges together," he said. "From a statistician's point of view it's a lot more complicated than that." Shao pointed out that each study differed in sample size, doses of soy, duration and gender inclusion. Besides, he said, the benefits of soy and soy protein with respect to cholesterol levels seems to be best for those at highest risk, with LDL cholesterol levels above 160 and total cholesterol above 250. "This study doesn't show any difference there. I'm not sure they have managed to sway anyone."
"FDA is evaluating the science," an agency spokesman said. "FDA may determine that a re-evaluation of a health claim may be needed when new scientific evidence does not support the current claim."
According to a report published by SPINS and Soyatech, soyfoods commanded a $4 billion U.S. market in 2004.