Does Soy Have a DARK SIDE?
Author/s: Sally Eauclaire Osborne
Issue: March, 1999
You've heard about the research touting soy's benefits, but some experts say you haven't heard the whole story.
ON THE LAND OF HEALTH FOODS, SOY IS KING. It's considered a near-perfect protein, one that's packed with compounds that can fight disease and promote health. Soy's plant estrogens--isoflavones--are said to prevent cancer, cut cholesterol, reverse osteoporosis, and wipe out menopausal symptoms. Earl Mindell, Ph.D., a registered pharmacist and author of Earl Mindell's Soy Miracle (Simon & Schuster, 1995), joins many nutritionists and doctors when he says, "Anyone who wants to live longer should be eating this food."
Yet a few scientists think the coronation of soy as a miracle food is premature. They claim that while some soyfoods offer distinct health benefits, others pose health risks, particularly to people who consume large amounts of soy. Critics cite four main potential dangers associated with eating too much soy or too much of certain kinds of soyfoods: One, soyfoods can disrupt the functioning of the thyroid gland: two, soyfoods can interfere with the digestion of proteins: three, they contain substances that rob the body of minerals: and four, soy's isoflavones may upset hormone balance.
How the Controversy Began
As early as 1917 researchers noted that soybeans had to be heat-treated in order for soy-fed rats to grow--presumably because soy contains a substance that inhibits digestion. Over the years, scientists have reported other potential problems with soy In this decade two women--Mary G. Enig, Ph.D., a fellow at the American College of Nutrition and a nutritional biochemist in Silver Spring, Md., and Sally W. Fallon, editor of the Price-Pottenger Nutrition Foundation Journal, which reports on the dietary habits of indigenous peoples--sought to make sense of these studies.
In 1995, Enig and Fallon believed they had found enough research to support certain charges against soy, particularly the concerns over thyroid inhibition, protein digestion, and mineral absorption. They wrote an article for the September 1995 issue of Health Freedom News--a publication of the nonprofit health advocacy group called National Health Federation in Monrovia, Calif.--in which they detailed these charges and cited dozens of scientific studies.
Enig and Fallon do not believe all soy products are equally suspect. "Some beneficial factors may appear in soyfoods prepared by traditional fermentation methods, such as miso, tempeh, and natto," Fallon says. Fermentation involves a slow chemical change triggered by bacteria, molds, or yeast. Enig and Fallon state that this process eliminates soy's problems by making it more digestible and deactivating potentially harmful substances. They see more problems with nonfermented soyfoods: tofu, soymilk, texturized soy protein, and soy protein isolate. (For definitions, see "Soy Glossary" on the next page.)
Since the 1995 article, other researchers have reported that soy may adversely affect hormones and have questioned the claims that soy fights cancer (see "Genistein and Cancer: Enemies or Allies?" on page 158).
After reviewing a few of the studies on the adverse effects of soy, Alan R. Gaby, M.D., a nutrition professor at Bastyr University in Kenmore, Wash., says, "I certainly think caution is reasonable. Soy is probably beneficial in moderate amounts, possibly harmful in larger amounts."
Meanwhile, as researchers debate these charges, some nutritional counselors have begun to suspect that soy may be to blame for the low energy, digestive disturbances, hypothyroidism, infertility, and other ailments they see in clients.
Brian R. Clement, director of the Hippocrates Health Institute, a raw foods, vegan clinic in West Palm Beach, Fla., says, "People come to us unshakeable in their belief that tofu, soy burgers, soy this, soy that are all good for you. They're not." Clement says his clinic staff has found it three times more difficult to bring the blood chemistry of people on a heavy soy diet to optimal levels than to improve the blood chemistry of people who eat little or no soyfoods. (Blood chemistry, according to Clement, includes everything from iron levels to pH balance.)
A number of scientists disagree with Clement. Mark Messina, Ph.D., a former program director in the diet and cancer branch of the National Cancer Institute and co-author of The Simple Soybean and Your Health (Avery, 1994), responds, "I'm not saying those stories are poppycock, but it bothers me as a scientist when anecdotal data is given too much credence. The problems might not be from soy. What else were those people consuming? The way to know is to look at published scientific studies. Researchers who have looked hard for adverse effects haven't found many."
Below we take a look at the research and at what some experts think about the charges lodged against soy.
Does Soy Disrupt the Thyroid?
The thyroid gland in the front of the neck secretes thyroid hormones and controls metabolism. Several scientists have linked soy consumption to suppressed thyroid function, including hypothyroidism (in which the gland produces not enough hormones). Researchers at the North Shore University Hospital-Cornell University Medical College in Manhasset, N.Y., found that children with autoimmune thyroid disease had consumed significantly more soy-based milk formulas than had their healthy siblings and other healthy children. These findings were published in the Journal of the American College of Nutrition in 1990. One year later, a 1991 Japanese study published in the Japanese journal Nippon Naibunpi gakkai Zasshi showed that soybeans could trigger goiters (an enlargement of the thyroid) and hypothyroidism. Half of the 17 healthy adult participants who ate 30 g of pickled roasted soybeans a day for three months developed a small goiter and/or experienced hypothyroidism. One month after the study was completed, all thyroids had returned to normal size and hypothyroidism symptoms such as constipation and fatigue had disappeared.
Some experts, however, believe that only certain people are apt to develop hypothyroidism from eating soy. "For soy to actually cause hypothyroidism, you'd have to be bordering on hypothyroidism to begin with," says naturopath Martin Milner, N.D., president of the Center for Natural Medicine in Portland, Ore., and developer of a new treatment for hypothyroidism.
And the amount of soy a person eats may also determine whether this food interferes with thyroid function. "I don't think you can get into trouble if you eat a few soyfoods within the bounds of a balanced diet," as long as you don't have a compromised thyroid system, says Daniel R. Doerge, Ph.D., a researcher at the Food and Drug Administration's (FDA) National Center for Toxicological Research in Jefferson, Ark., who has isolated and studied the "anti-thyroid" components of soy. "But I see substantial risks from taking soy supplements or eating huge amounts of soyfoods for their putative disease-preventive value. There is definitely potential for interaction with the thyroid."
Does Soy Contain Digestion Blockers?
Some researchers consider soy difficult to digest because it inhibits the functioning of the pancreatic enzyme called trypsin. The body needs trypsin to properly digest protein. But all legumes have substances called trypsin inhibitors that interfere with the work of this enzyme. (Soy is thought to have more of these inhibitors than other beans.) When there is less trypsin, more undigested and partially digested protein molecules move through the digestive tract.
Mindell acknowledges that mw soybeans do contain trypsin inhibitors. "But who's eating raw soybeans? No one," he says. "Processing and cooking deactivates all the trypsin inhibitors."
Biochemist Irvin E. Liener, Ph.D., professor emeritus at the University of Minnesota, reviewed the studies done on trypsin inhibitors and concluded that most soyfoods on the market retain 5 to 20 percent of the trypsin-inhibitor activity of raw soybeans. His findings appeared in the Journal of Nutrition in 1995. In that same issue, researchers Robert L. Anderson, Ph.D., and Walter J. Wolf, Ph.D., of the U.S. Department of Agriculture's (USDA) National Center for Agricultural Utilization Research in Peoria, Ill., reported that fermented soyfoods such as miso and soy sauce generally have lower levels of trypsin inhibitors than soyfoods that are processed and cooked but not fermented.
Some researchers point out that eliminating all trypsin inhibitors may not be ideal. While high levels of these inhibitors have triggered what appear to be premalignant lesions in the pancreases of animals, low levels may have cancer-fighting and cancer-preventing abilities. What's unknown is the level to consume for optimal health. Liener wrote: "If soybean trypsin inhibitors are to be recommended for their anticarcinogenic effects, it becomes important to establish the upper limit of exposure at which one can expect this preventive effect against cancer but beyond which one runs the risk of incurring adverse effects that have been generally ascribed to the protease inhibitors [which include trypsin inhibitors]."
Does Soy Prevent the Absorption of Minerals?
The bran or hulls of seeds, found in beans, grains, nuts, and other plant foods, contain phytates (or phytic acids). These phytates bind to essential minerals such as calcium, iron, and zinc in the digestive tract and prevent them from being absorbed.
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