Soy does not reduce LDL cholesterol levels

A reduction in low density lipoprotein cholesterol (LDL) by just a few points reduces the risk of heart disease and stroke. Some studies showed that replacing animal protein in the diet with soy protein lowered total cholesterol and LDL cholesterol levels. Soy increases the activity of liver enzymes that break down cholesterol. In 1999, the U.S. Food and Drug Administration recognized the claim by soy manufacturers that a diet containing 25 grams of soy protein per day is good for the heart and lowers cholesterol. A year later, the American Heart Association recommended that people with an increased risk of heart attack should include soy products in their diet.

Unfortunately, there was little conclusive evidence that soy is good for the heart or that it lowers blood cholesterol levels. Most of the studies that did show positive effects used very few subjects and often had statistical and study design problems.

The American Heart Association changed its position in 2006 and concluded that soy protein or isoflavones (estrogen-like chemicals in soy products) do not lower LDL cholesterol, triglyceride levels or blood pressure, nor do they raise HDL cholesterol (the "good" cholesterol).

Australian scientists confirmed this when they found that high soy protein consumption had no effect on total cholesterol or LDL cholesterol levels.

However, eating soy hamburgers and soy hotdogs instead of their animal counterparts, which are rich in saturated fat, could reduce saturated fat intake and thus improve cardiovascular health. Although soy products do not have a direct effect on cholesterol metabolism, they may improve the overall quality of the diet.
(WebMD Health News, August 8, 2008; American Journal Clinical Nutrition, 88: 298-304, 2008)