We've been told eating soy-based foods lowers cholesterol, chills hot flashes, prevents breast cancer and prostate cancer, promotes weight loss, and wards off osteoporosis. That’s not the whole soy story, says the Harvard School of Public Health (HSPH).
“While some of soy’s touted benefits are attributed to a unique characteristic: its high concentration of isoflavones, a type of plant-made estrogen (phytoestrogen) that mimics naturally-produced estrogen, many health claims about soy go far beyond the available evidence,” HSPH said.
In 1999, the Food and Drug Administration let companies claim that foods containing soy protein "may reduce the risk of heart disease." The claim was based on early research showing that soy protein lowered levels of low-density lipoproteins or LDL (bad) cholesterol.
A 1995 meta-analysis, published in the New England Journal of Medicine, of 38 controlled clinical trials showed that eating approximately 50 grams of soy protein a day in place of animal protein reduced total cholesterol levels by 9.3 percent, LDL cholesterol by 12.9 percent, and triglycerides by 10.5 percent.
If such reductions were sustained over time, heart attack, stroke or other cardiovascular disease could be reduced by 20 percent.
The American Heart Association’s (AHA’s) nutrition committee looked at more recent soy-cholesterol research and says the results aren’t so glowing. It found eating 50 grams of soy daily—more than half the average person’s daily protein requirement— lowers LDL about 3 percent.
To get 50 grams of soy protein, a person has to eat one-and one-half pounds of tofu or drink 64 ounces of soy milk.
There’s still a silver lining. The AHA committee says that even though soy protein itself has little direct effect on cholesterol, soy foods are still good for the heart and blood vessels.
This is because they usually replace less healthful choices, like red meat while delivering plenty of polyunsaturated fat, fiber, vitamins, and minerals, and low saturated fat.