A New Look At The Soybean
Great--but not a Panacea
Charles R. Attwood, M.D., F.A.A.P.
he soybean, judging from comments by my colleagues, patients and readers, seems to have attained the status of a matinee idol -- almost always the hero. Occasionally, and not unexpectedly with its constant aura of mystique, it has been cast in the role of a villain. Stardom didn't come overnight for this mainstay of the Asian diet, which was considered by the ancient Chinese to be one of the five sacred grains, along with rice, wheat, barley, and millet. It dates back to 2838 B.C. in China, the 6th century in Japan, and the 17th century in Europe. The United States became interested, despite its bland flavor, in the 1920s, when its full nutrient value and inexpensive production were finally appreciated. Now our country grows one-third of the total world supply, mostly for livestock feed and non-food commercial products.
Surprisingly, only 2 percent is destined for human consumption, in the form of soybean oil, tempeh, miso, tofu, soy milk, soy flour, soy sauce and the dried bean. Fresh soybeans are not generally available except in Asian markets or specialty produce markets in late summer and early fall.
The soybean may have been a lifesaver at times in world history when calories were inadequate. Examples were the POWs of World War II, and more recently, the residents of Cuba during the 34 year embargo. In both instances, the soybean was credited with preventing starvation and death. Its value is no less in calorie-rich societies, such as the United States and most Western countries, where soybeans, like oat bran, have been shown to reduce cholesterol levels when replacing animal proteins in the diet. This is probably due to its richness in soluble fiber and the fact that it replaces some of the saturated fat in the diet.
Because of its high protein content, many individuals have been under the impression that a proper plant-based diet must include soy products, in combination with other "less complete" protein sources. Unfortunately, in this respect, the famous bean has probably frightened away some individuals who would have benefited from a meatless diet. Patients in my clinic often say that the prospect of rounding out their daily menu with tempeh or tofu is less than appetizing.
Vegetarianism, in general, may have been somewhat tainted by this soy association for decades. Francis Moore Lapee, in her 1971 groundbreaking book, Diet for a Small Planet, dispelled the myth that meat was needed for complete proteins. Her solution -- carefully combining vegetable proteins -- she said in the 1991 edition, "reinforced another myth." Now, she said, "If people are getting enough calories, they are virtually certain of getting enough protein." Her sample plant-based menu, which exceeded the protein requirements of the National Academy of Sciences, contained no soy products.
She was right; in recent years it has been found that such careful food-combining isn't necessary. This best-seller -- over 3 million and still going -- also popularized the concept that fermented soy products, such as tempeh and miso contained significant amounts of vitamin B12. But more recent assays show that this is an inactive B12 analogue, not utilized as the vitamin in human consumption; and according to some investigators, may block actual B12 metabolism.
Suzanne Havala, M.S.,R.D., author of the American Dietetic Associations's position paper on vegetarian diets and the new book, Shopping For Health, recently told me, "It isn't necessary that people who dislike miso, tofu, or tempeh have to eat them or other soy products in order to get adequate quality proteins. Havala agrees that a variety of plant matter will do as long as the individual consumes enough calories.
"Soy products," she said, "on the other hand, are nutrient-dense and a very good choice." She adds that their taste has improved in recent years and she doesn't personally consider them bland. So like any legume, the soybean is nutrient-packed, but unlike other beans, there may be a few caveats to consider before eating unlimited amounts of soy products. First, in my practice, I have found that allergies to the soybean are far more common than to other legumes. Newborn infants seem to tolerate commercial soy formulas very well, but according to the American Academy of Pediatrics, this early exposure may be causing some of the soy allergies I'm now seeing in in older children and adults. Pediatric allergist, Brent Prather, of Lafayette, Louisiana, agrees. He tells me he sees far more soy allergies in children than his pediatrician father did before commercial soy formulas came into common use in the 1960s. Second, soybeans are 60 percent oil and a significant, source of fat that can add as much as 9 grams per serving (one-half cup cooked beans or a three and one-half ounce block of tofu) -- one-sixth of it is saturated. When combined with other ingredients in American dishes, soy typically adds about 5 grams of fat per serving.
And finally, some recent reports suggest that precipitated soy products, such as tofu, if consumed regularly, may inhibit the absorption of such minerals as calcium, magnesium, iron, and especially zinc.
The word "soybean" on a food label doesn't always mean good nutrition. Often, the opposite may be the case. Soybean oil is used in hundreds of processed foods, especially snacks, salad dressings, and margarines, in a partially hydrogenated form made more saturated by adding hydrogen atoms. This altered version, known as a trans fatty acid, is everywhere, Graham crackers, Ginger Snaps, even SnackWell's. Like natural saturated fat, it appears to raise cholesterol levels, but also lowers HDL. Here, one should watch the ingredient portion of food labels -- hydrogenated oils are not identified alongside total and saturated fat.
In summary, even though the soybean is an excellent source of protein and fiber, and a good choice, it's no panacea and isn't mandatory for a well-balanced, plant-based diet. Complete, high-quality vegetable protein is assured by a variety of vegetables eaten within one day -- not necessarily in one meal--assuming adequate calories are consumed. So keeping in mind its fat content, proneness to allergy, and possible interference with mineral absorption, let's say that a moderate consumption, along with a variety of vegetables and other legumes, would be prudent for both children and adults.
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