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If you've been in a supermarket lately, you couldn't help but notice that soy is, well, everywhere. It's the new star ingredient in cereals, energy bars, and chips, as well as in imitation meat and dairy products from cold cuts, burgers, and chicken, to milk, cheese, yogurt, and ice cream.
What's with the soy surge? For starters, after decades of trial and error, food makers finally got a handle on how to produce soy-based foods that Americans will eat. Home cooks who may have been confounded by squishy blocks of tofu know exactly what to do with soy burgers and soy deli meats. And the taste has improved -- dramatically. "It took a while for manufacturers to make soy foods that didn't taste 'beany,' but they've finally done so," says John Erdman, PhD, professor of food science and human nutrition at the University of Illinois at Urbana-Champaign.
A major catalyst for the soy-foods explosion was the FDA's announcement five years ago that eating 25 grams of soy protein a day (as part of a diet low in saturated fat and cholesterol) lowered cholesterol sufficiently to reduce the risk of heart disease. In its history, the FDA has issued only 12 such food-related health claims. This one was based largely on a 1995 review of 38 studies, published in The New England Journal of Medicine, that showed that eating soy protein instead of animal protein -- say, grilling up soy burgers instead of beef patties or using soy milk on your cereal instead of whole cow's milk -- significantly lowered total cholesterol, LDL ("bad") cholesterol, and triglycerides.
Soy became an overnight superfood. Manufacturers slapped the health claim on any product containing at least 6.25 grams of soy protein per serving, the minimum amount required by the FDA. And consumers started gobbling up these products. The year the health claim came out, soy sales saw a 31 percent increase, and the market has grown an average of 14 percent a year ever since. According to the United Soybean Board, 28 percent of us now buy soy foods once a week or more, mainly because we believe they're healthy.
Soy is a lean plant protein that's packed with vitamins and fiber and has zero cholesterol and minimal saturated fat. However, our understanding about what it is about soy that makes it so healthy is still evolving. At first, some scientists suspected soy's cholesterol-lowering effect was in part due to its high levels of isoflavones, a collection of plant chemicals with weak estrogen-like characteristics. But now, scientists believe that isoflavones do not play a role in lowering LDL and triglycerides. Instead, it seems that the soy protein by itself may play a small role in lowering cholesterol.
Small, however, may be the operative word. Now some scientists are questioning whether soy reduces cholesterol to any significant degree, or whether people who eat a diet rich in soy foods simply eat less of other cholesterol-laden foods that would otherwise raise LDL cholesterol and contribute to cardiovascular disease. Several important studies in the past two years have shown only a very tenuous link between soy and cholesterol reduction. "The bottom line is that there's really no proof that soy protein lowers LDL cholesterol significantly enough to be therapeutic," says Robert H. Eckel, MD, professor of medicine at the University of Colorado Health Sciences Center, in Denver, and chair of the American Heart Association's Council on Nutrition, Physical Activity, and Metabolism. A spokesperson for the FDA said the agency is evaluating the new research but so far has not altered its soy health claim.
Some research shows that eating soy seems to lower cholesterol significantly -- some 5 to 10 percent -- only in people who have very high cholesterol to start with. But ultimately, if your cholesterol is in the danger range, whether soy reduces it by 5 percent or 10 percent hardly matters. "You can't get from an LDL concentration of 200 mg/dl to 100 mg/dl with an agent that lowers cholesterol that little," says John Crouse, MD, professor of medicine and public health sciences at Wake Forest University School of Medicine, in Winston-Salem, North Carolina. "If you have high cholesterol, eating soy is not the answer. You probably need statin drugs. But soy can still be part of a heart-healthy diet."
It's best to approach soy as part of a healthy eating plan, not as a magic bullet. "We need to stop focusing on one particular food, and eat a number of foods known to benefit heart health," says Clare Hasler, PhD, executive director of the Robert Mondavi Institute for Wine and Food Science at the University of California, Davis. "For some people who eat heart-healthy oatmeal for breakfast, a handful of omega-3-rich nuts for a snack, and a glass of soy milk in the course of the day, it's conceivable that such a diet, over time, could be an effective treatment for lowering cholesterol."
"If people use soy protein to replace animal proteins such as those found in cheese, steak, or hamburger, they displace saturated fat from their diets, and that can significantly decrease LDL cholesterol levels and lower their risk for heart disease," says Alice Lichtenstein, Gershoff professor of nutrition science and policy at the Friedman School of Nutrition Science and Policy at Tufts University, in Boston. "But by just eating cereal with 6.25 grams of soy protein per serving, I don't think they're going to get the health benefit they're hoping for."
Even if soy doesn't lower cholesterol as much as once thought, it's important to remember that cholesterol is only one piece of the heart-disease puzzle. Future studies may find that soy works to fight disease in ways that scientists haven't even thought of yet.
Originally published in Ladies' Home Journal magazine, April 2004.