Not long ago, you could say “tofu” and your companion would think you’d just sneezed. Few people (with the exception of Asians or vegetarians) had heard of tofu, much less knew how to cook it. The genuine article was found only in Chinese restaurants and health-food shops — even then, its purveyors might not have been totally sure what the off-white cheeselike product was made of.
Nowadays, tofu, tempeh and other foods made from soybeans can be found in any supermarket. Touted as a miracle food for nearly a decade, the “king of the legumes” has reigned supreme as a remedy for everything from heart disease to hot flashes.
Lately, however, soy’s crown has slipped a bit. A recent report on soy overturned the 2000 conclusion by the American Heart Association (AHA) that it lowers LDL (“bad”) cholesterol. Other critics, such as Kaayla T. Daniel, author of The Whole Soy Story: The Dark Side of America’s Favorite Health Food (New Trends Publishing, 2005), say that soy has become ubiquitous in the American diet and that consumers unknowingly ingest far more of it than is healthy.
This soy overload has been blamed for everything from increased risk of breast cancer and thyroid problems to brain atrophy. What’s the real scoop?
The soybean (Glycine max) is a legume native to China. It offers a “complete” protein profile, a real plus for vegetarians and those who are allergic to cow’s milk. Soy is a good source of magnesium, potassium, phosphorus, calcium and manganese, and is high in fiber and B vitamins.
Used for centuries in China, both soy milk and tofu are said to have been invented by Lui An, grandson of the founder of the Han dynasty, in about 164 B.C. Throughout China, Japan and Korea, the soybean is a significant part of the diet in its many various forms. Tofu, tempeh, miso and natto are all processed soy products, as is shoyu (soy sauce). Edamame are soybeans boiled in the pod and served with salt as a popular snack.
Population studies in the past 30 years have shown that Asian women with a high-soy diet generally have lower rates of breast cancer than women in the United States and other
Western countries. But a recent analysis conducted by researchers at Georgetown University Medical Center and Johns Hopkins School of Medicine found the data too inconsistent to recommend soy as a breast cancer preventive.
The report, published in the April 2006 issue of the Journal of the National Cancer Institute, was a meta-analysis of epidemiologic studies from 1978 to 2004 and found that consumption of soy foods in amounts consistent with an Asian diet was not detrimental to breast health. However, the authors cautioned against overuse of soy supplements, especially by women at high risk for breast cancer, or who are breast cancer survivors.
Soy contains isoflavones, plant estrogens that are similar to estrogen present in the body. For some women, too much soy in the form of supplements might prove to be dangerous. In the same way that estrogen-based hormone replacement therapy is unsafe for women at high risk of developing breast cancer, soy isoflavone supplementation also should be considered unsafe, the researchers said.
Leena Hilakivi-Clarke, Ph.D., one of the coauthors of the study, explains, “There is no evidence that consuming soy increases postmenopausal breast cancer risk — and it may, in fact, reduce premenopausal breast cancer risk.” But she was not as sanguine about nonfood soy supplements. “Estrogens make the breast tumor cells grow. Although we found that soy food intake was associated with a reduced breast cancer risk, we have no idea what soy supplements might do.”
Whether soy is beneficial or not to breast health, “is a much more complicated picture than we’d originally thought,” says Charles Wood, M.D., a researcher and instructor of pathology at Wake Forest University who also studies the role of hormonal agents in postmenopausal breast cancer risk. “It appears that certain populations of women benefit by increasing soy in the diet. There is little evidence that soy protein intake has an adverse effect when eaten as part of a healthy diet,” Wood says.
Iodine is necessary for proper thyroid function, and it has been added to table salt since 1924 in order to eliminate goiter (the enlargement of the thyroid gland). The incidence of goiter in animals that eat large amounts of soy has caused concern about its deleterious effect on thyroid function in humans. However, studies reveal that goiter occurs only when soy intake is very high and iodine intake is very low. Goiter in infants who were fed soy formula was reversed when they began receiving iodine.
The elderly, who often limit salt due to hypertension, should be aware of and monitored for possible thyroid problems resulting from consumption of soy products. Postmenopausal women who consume large amounts of soy products may be at higher risk. Those who must limit salt should be sure to eat iodine-rich foods, such as seafood, sea vegetables, low-fat dairy foods and spinach.
For the past six years, “Eat soy to protect your heart” has been the mantra of government and private health agencies. This was because of a study in 2000 that led the AHA to conclude that as little as 25 grams a day of soy protein could reduce LDL cholesterol by as much as 8 percent.
But scientists recently have questioned that conclusion. A review of 22 studies reported in January 2006 failed to confirm that soy protein has favorable effects on cardiovascular health. The report states: “No significant effects on HDL cholesterol, triglycerides, lipoprotein or blood pressure were evident. Among 19 studies of soy isoflavones, the average effect on LDL cholesterol and other lipid risk factors was nil.” According to the AHA’s Nutrition Committee, those early studies that found soy lowered LDL cholesterol were overly positive. In light of the 2006 review, the AHA said, it “could not recommend the use of isoflavone supplements in pills or food for the prevention of heart disease.”
But Alice Lichtenstein, D.Sc., a nutrition scientist at Tufts University and the chair of the AHA’s Nutrition Committee (who coauthored the updated report), notes that this doesn’t mean to stop eating soy. “Soy is a great food,” Lichtenstein says. “It is low in saturated fat and is a good-quality protein.” Replacing meat, cheese and high-fat animal proteins with soy is still “a win.”
There is other positive news for soy lovers: It could help prevent bone fractures. For five to seven years after a woman reaches menopause, she will experience bone loss at the rate of 3 to 5 percent per year. “Soy consumption has been shown to modulate bone turnover and increase bone mineral density in postmenopausal women,” writes Xianglan Zhang, M.D., of Vanderbilt University’s School of Medicine.
Between March 1, 1997, and May 23, 2000, approximately 75,000 Chinese women aged 40 to 70 years were enrolled in the Shanghai Women’s Health Study. When researchers followed up with the study’s participants, they found that risk of bone fractures decreased with increased soy intake.
“Soy food consumption may reduce the risk of fracture in postmenopausal women, particularly among those in the early years following menopause,” Zhang says. “Soy or soy isoflavones may exert their effects on bone by suppressing bone resorption, while at the same time stimulating bone formation.”
A study six years ago by Lon White, M.D., of the Pacific Health Research Institute, suggested that there was a positive correlation between brain atrophy (Alzheimer’s disease) and tofu consumption. However, this was a single study and by itself failed to prove that soy isoflavones cause brain atrophy. The U.S. Food and Drug Administration (FDA) rejected it, finding the research not complete enough to be useful.
The agency commented that if tofu or soy products really did cause Alzheimer’s disease, the incidence of the disease would be higher in Japan, where consumption was higher, than in Hawaii, where the study was conducted. This was not the case. Therefore, the FDA was not persuaded, discounting “concerns about potential adverse effects of soy protein in dementia and brain atrophy in older persons.”
John J. B. Anderson, Ph.D., professor of nutrition at the University of North Carolina, Chapel Hill, takes soy-bashing in stride. “Soy is a good food, not a magic bullet,” he says. “People are being hard on soy lately; mainly because we now know it is not so beneficial to the heart as once thought. Still, soy contains polyphenols and antioxidants. It contains a lot of good nutrients, including protein and fiber.”
Anderson advocates a “food first” approach, as many soy experts do. “Don’t throw soy out,” he recommends. “Just consume it wisely.”
Nancy Allison is a freelance writer and illustrator living in Fort Worth, Texas. She is a frequent contributor to Herbs for Health.
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