The New Low-Cholesterol Diet: Soy

Soy protein can be a meal, a side dish, a snack or a drink. Made from the soybean, it's a staple of Asian diets. Yet it's largely been the butt of jokes about hippies and vegans -- until recently. Today, the buzz about soy is serious. Can it lower cholesterol naturally? Some studies say yes. But, unfortunately, research shows mixed results. We may not know the answer for years.

How Might Soy Protein Help?

A number of studies over the past decade seemed to show soy protein could lower "bad" LDL cholesterol and triglycerides without lowering "good" HDL cholesterol. Researchers aren't exactly sure how soy protein might help. It could be a combination of the effect of the protein and natural chemicals in soy called isoflavones. But in January 2006, the American Heart Association announced some surprising news. A review of 22 clinical studies concluded that eating soy-based foods has only minimal impact on cholesterol and other heart-disease risk factors.

Until further research clears up the controversy, should you dump soy from your diet? Not at all, says Tufts University nutrition researcher Alice Lichtenstein, DSc, who helped write the AHA statement. "Soy is a great food. It is low in saturated fat and it is a good-quality protein," she says -- even if its heart benefits are less than expected.

Conflicting Evidence on Soy

There have been many studies of the effects of soy on cholesterol. One major 1995 article published in the New England Journal of Medicine found that replacing animal protein with soy protein could lower levels of total cholesterol, bad LDL cholesterol, and triglycerides. At the same time, it didn't significantly lower levels of "good" HDL cholesterol.

Some recent studies have shown that soy protein, when eaten along with other cholesterol-lowering foods, can have a big effect. In a study published in the American Journal of Clinical Nutrition in 2005, researchers tested cholesterol-lowering drugs against cholesterol-lowering foods in a group of 34 adults with high cholesterol. People ate 50 grams of soy protein daily along with other cholesterol-lowering foods. The results were striking: the diet lowered cholesterol levels about as well as cholesterol drugs.

However, not all studies agree. A 2005 analysis of various studies led by the U.S. Agency for Healthcare Research and Quality found that soy had a modest effect on cholesterol levels. Researchers found that eating a high amount of soy -- equal to about a pound of tofu a day -- only added up to a 3% reduction in "bad" cholesterol levels.

Based on those more recent studies, the AHA Nutrition Committee no longer recommends eating soy specifically to lower cholesterol. However, the AHA does consider soy burgers and other soy foods a healthy replacement for high-fat meats.