JUNE 7, 1999; VOL. 153 NO. 22
By CHRISTINE GORMAN
Worried about high cholesterol? This versatile bean may be just what the doctor ordered
Dolores Pilcher, 67, a retired nurse living in Mount Airy, N.C., knows her risk of heart disease only too well. Both her father and an aunt died of heart attacks when they were still pretty young, and her cholesterol level has soared over the past few years. So when she heard that scientists were trying to determine if drinking a soy-protein milk shake every day could lower cholesterol levels, she volunteered to take part in the experiment. To Pilcher's delight, the total amount of cholesterol in her blood fell from 245 mg/dl to 205 mg/dl and the level of LDL, or "bad cholesterol," fell from 170 mg/dl to 130 mg/dl. Now that the study is over, she still sprinkles soy powder on her cereal every morning, with the same salutary results.
Pilcher's success is being repeated all across the U.S. as a growing number of Americans discover that soybeans aren't just for livestock and vegetarians anymore. Doctors are studying its potential to lower cholesterol, fight cancer and build healthy bones. Grocers are stocking tasty new varieties. And sometime this summer or early fall, the U.S. Food and Drug Administration is expected to put soy on its short list of foods that may actually lower the risk of heart disease. (The others are fiber-containing fruits, vegetables, whole grains and psyllium seed husk.)
We're not talking about some watery bean curd from the 1960s either. Soy chefs have figured out all sorts of ways to shape, process and blend soy protein so that it isn't just good for you but tastes good too (though they still don't seem to have "chicken" right). The tricky part, medically speaking, is figuring out what soy foods can and cannot do to protect your health.
The best evidence to date has to do with soy's ability to lower cholesterol. Over the past 25 years, some three dozen studies have shown that eating as little as 47 g, or about 1.5 oz., of soy foods can lower total cholesterol levels an average of 9% and LDL 13%. (Just in case you're keeping score, that's about the same cholesterol-lowering effect as that promised by Benecol, the new high-priced margarine approved by the FDA two weeks ago.) But every little bit counts, since each 1% drop in total cholesterol translates into a 2% drop in the risk of developing heart disease. Still unclear is whether soy can help everyone or just those folks who have high cholesterol (over 240 mg/dl) to begin with.
That's not the only mystery. Scientists are almost embarrassed to admit that they still don't know why soy lowers cholesterol levels in the first place. For a long time they believed the key ingredients to be isoflavones--which sounds like the name of a new rock band but in fact refers to a group of naturally occurring plant chemicals that weakly mimic the effects of estrogen hormones in some parts of the body while acting like antihormones in others.
Since estrogen is known to protect the heart, it stood to reason that isoflavones might too. But when scientists fed purified isoflavones in pill form to test subjects, their cholesterol levels didn't budge. Now some researchers are focusing on the composition of the protein in soy to explain its potentially beneficial effects, while others argue that it's the combination of the protein and the isoflavones that does it.
Doctors are especially interested in how that dispute gets resolved, because whatever it is that makes soy special might also help protect against breast cancer. In Japan, where soy is a staple, the incidence of breast cancer is much lower than in the U.S. and other industrialized countries. (Japanese women also eat more fruits and vegetables and drink more green tea, so soy is just one possible explanation.) Here again the spotlight is on the isoflavones, although this time the compounds would have to act as antihormones, much like the cancer drug tamoxifen, since many breast tumors need estrogen to grow.
Alas, it isn't entirely clear that isoflavones work that way. In fact, one study done in rats suggested that they may actually promote rather than retard the development of breast cancer in some women. "I tell my patients to be cautious," says Dr. Victoria Seewaldt, a breast-cancer specialist at Ohio State University who happens to love tofu. "In the worst case, soy could possibly negate the protective effects of tamoxifen."
But if you're not at any great risk of breast cancer and you're worried about heart disease, soy could be just what the doctor ordered. Just keep in mind a few ground rules: for the best results, stick as close to the original bean as your palate will allow. Boiled soybeans (edamame) are surprisingly tasty. Tofu, or bean curd, just needs the right sauce, like a spicy curry. (It's safest to buy blocks in individually wrapped containers, however, to protect against bacterial contamination.) Soy milk is O.K. on cereal but will ruin a good cup of coffee. Watch the salt in miso soup if you happen to be sensitive to it.
If that sounds like too much work, then consider some of the many soy powders and concentrates on the market. Choose one that wasn't extracted with alcohol, a process that removes most of the isoflavones. Whether you sprinkle it on your cereal or add it to a shake, the FDA recommends eating about 25 g of soy protein a day.
Stay away from isoflavone supplements; the stuff probably won't do you much good by itself and could lead to problems in high doses. And check the label on all those soy hot dogs, sausages and pork ribs. Some are made with textured vegetable protein that doesn't contain a lot of soy, while others have plenty of soy protein but no isoflavones.
Finally, don't expect miracles. A splash of soy sauce on your fried wonton won't do a thing for your arteries. (Soy sauce, besides being too salty, is almost isoflavone-free.) You still have to stop smoking, cut down on the amount of saturated fat in your diet, load up on fruits and vegetables and get plenty of exercise. But if you're already eating an apple a day, you can't go wrong adding an ounce or two of soy.
--WITH REPORTING BY UNMESH KHER/NEW YORK
-- Soybeans, one of the world's most important leguminous crops, don't grow in the wild. They were first cultivated by prehistoric Chinese from a rambling, climbing vine.
-- The Japanese consume more than 50 lbs. of tofu per person per year.
-- Half the world's soybeans are grown in the U.S., which exports a third of its crop.
-- Up to 95% of soybeans used in the U.S. wind up in animal feed.
Not all soy foods are alike
Processing makes a big difference; some soy products have lots of isoflavones, some none at all.
Here's a rough guide:
Soy isolate (1 oz.) -- 60 mg
Soy flour (1/2 cup) -- 50 mg
Tofu (4 oz.) -- 30 to 40 mg
Soy milk (1 cup) -- 30 to 40 mg
Soy sauce -- 0
Soy oil -- 0