SOY. The symbiosis between the soy plant and Rhizobium bacteria in the soil underlies the soybean's success as a major source of protein for human populations in Asia and domesticated animals in many countries, as well as an important renewer of land fertility in traditional agriculture. Rhizombium bacteria enter the root hairs of the soy plant (and those of other legumes), helping to form nodules where they feed on the plant's carbon supply. In exchange, the bacteria convert atomospheric nitrogen gas in the soil to ammonium, rendering the nitrogen accessible to the soy plant for use in protein synthesis. The resulting soybean is high in amino acids in ratios that make it, when compared to other known plant sources of protein, strikingly "complete" as a human food. Additional benefits are imparted when legumes such as soy decay. Bioavailable nitrogen is released into the soil, becoming accessible to other plants that lack symbiotic relationships with nitrogen fixing bacteria. Soy and other legumes have therefore played a crucial role in crop–rotation farming, contributing to the growth of other crops and pasturelands. Soybeans are also high in oil content, and in the latter twentieth century became the world's top source of edible oil.
Physical Characteristics of the Soy Plant
Erect and bushy, the soybean plant can grow to over six feet high. It has ovate leaflets in groups of three; white, purple, or pinkish self–fertilizing flowers; and one to five beans in each pod. As with other legumes, at maturity the pod bursts open on both sides to expose the beans. Beans range in size from 1 to 3.5 centimeters or more and can be yellow, green, brown, black, reddish, or bicolored; their variations offer mute testimony to generations of selective breeding. The beans are 15 to 20 percent oil, and 35 to 45 percent protein, depending on the variety and farming conditions.
Timing of the soy plant's maturation is highly sensitive to day length; each variety requires a specific span of darkness to induce flowering. Known as photoperiodicity, this phenomenon makes the optimal choices of varieties different for each latitude where soybeans are grown. Soy's extreme photoperiodicity, along with its vulnerability to frost, probably slowed the early spread of its cultivation in China. Under the right conditions for any given variety, however, soy is a reliable crop that tolerates poorer soils. For this reason, in ancient China it was deemed invaluable as protection against famine should other crops fail.
Soy also has nutritional virtues beyond its protein and oil. Although their nutritional value varies with the growing conditions, in general the beans provide modest levels of vitamin A, vitamin E, thiamine, riboflavin, other B–complex vitamins, potassium, phosphorus, magnesium, calcium, and iron.
Origins, Domestication, and Diffusion of Soy
The soybean, Glycine max, is a cultigen that apparently does not exist in the wild. Botanists believe its wild ancestor was Glycine ussuriensis, a vine native to Taiwan, Korea, Japan, the north–central and far northern areas of eastern China, and adjacent areas of Russia. Chinese legend has it that sometime between about 2800 and 2400 B.C.E., the Emperor Shen Nung, father of Chinese agriculture, first extolled the virtues of the soybean in writing. Contemporary sinologists believe, however, that Shen Nung's famous treatise—indeed, Shen Nung himself—are the inventions of a much later era. As Theodore Hymowitz details in his "On the Domestication of the Soybean," botanical, archaeological, and linguistic research suggest instead that the trial-and-error process of domesticating soy began during the Shang Dynasty (circa 1600 B.C.E.–1027 B.C.E.), and that Glycine max did not emerge as a successful domesticate until the eleventh century B.C.E., probably in the north-central section of eastern China.
Soy cultivation gradually spread; evidence suggests that by the first century C.E., it had reached northern Manchuria, Korea, central and south China, and northern Vietnam. The expansion and contraction of Chinese dynasties was probably instrumental in this spread, as were the activities of Buddhist missionaries, who encouraged soybean cultivation as an expression of their vegetarianism. Buddhists were also the likely agents of early soy cultivation in Japan, beginning around the sixth century C.E. The emigration of ethnic Thais from China during the seventh century C.E. spread soy agriculture to present-day Thailand; traffic along the Silk Road brought soy to the northern Indian subcontinent in the eleventh and twelfth centuries. Between the first century C.E. and the sixteenth, soy was also introduced to Indonesia, the Philippines, Malaysia, Burma, and Nepal.
In the twentieth century, the bulk of the world's soybean production shifted to the New World. Although soy was first cultivated in what is now the United States in 1765, it was not a leading U.S. crop until World War II. In the 1970s, South American nations also began expanding soy production. Today the primary growers are the United States, which produces about half the world's supply, Brazil, China, and Argentina.
Developments in Soy Agriculture—Demand and Supply
Demand. Unless adequately processed, mature soybeans are difficult for humans to digest and contain antinutritive components. In early centuries, the Chinese considered soybeans important yet undesirable—poor man's food. But once they learned to make palatable and nutritious processed soy products, beginning around the third century B.C.E., demand for soy increased. For centuries, however, the demand for soybeans in Asia had little influence elsewhere.
In the 1920s, soy oil was used in the United States for industrial purposes; by the late 1930s, research was improving its flavor for American palates. At that time, the oil was lucrative; the protein meal was a cheap by-product fed to animals. During World War II, with imports of foreign vegetable oils cut off, the U.S. government promoted a huge expansion of soybean harvesting. Although the oil commanded a higher price per pound, the enormous surplus of meal came to provide more overall profits as Americans—and gradually people in developed countries worldwide—began to eat far more meat than ever before.
Today some 95 percent of the soy meal used in the United States is consumed by meat-, egg-or dairy-producing animals. This pattern is repeated in numerous countries that import soy from the United States, such as Mexico and in Europe. Even in Japan, where soy protein is an integral part of human diets, more soy is used for animal feed than for human consumption.
Supply. Early in the twentieth century, the development of tractors and combines made profitable, large–scale soy farming possible in America. A system was developed for storing soybeans at the right conditions of temperature and moisture at processing plants and in giant grain elevators; the Mississippi River became a crucial artery for soy exports. Soy agriculture worldwide has benefited as well from research on managing pests and diseases, including programs for breeding pest-resistant varieties.
Breeding programs have also been critical to the success of soy farming in varying growing conditions and for various desired traits (for example, higher oil or protein content), beginning with Asian farmers' patient work over centuries. More recently, plant breeders developed varieties tolerant of equatorial latitudes, making cultivation of soy in tropical Brazil profitable.
Since 1996, soy genetically modified with a gene from bacteria has become popular among farmers in the United States and Argentina. This soy is engineered to tolerate the Monsanto company's herbicide, Roundup, enabling farmers to use the herbicide easily without killing their crop. In the year 2000, over 50 percent of soy acreage in the United States was planted with "Roundup Ready" (RR) soy; it is currently the most grown genetically modified (GM) crop in the world.
RR soy is present in minute quantities in a wide array of American processed foods. Nutritionist critics worry that it could provoke allergic reactions in sensitive individuals, although to date there is virtually no scientific evidence of such a problem. Environmentalists fear that the gene for resistance to Roundup could "jump" to other plants, creating superweeds. Although some scientific evidence may support this concern, so far the problem has not materialized. Prestigious organizations such as the National Academy of Sciences have called for more government supervision of GM crops, however. There is, as well, a small but growing market for organic, non–GM soy used to make foods high in soy protein ("soyfoods"), both in the United States and in other developed nations.
Modern Trade in Soy
In the early twentieth century, Europe and the United States imported Manchurian soybeans for oil. Beginning in 1930, however, tariffs protected the American soybean industry. Gradually, soybeans (whole, as meal, and as oil) became the America's primary agricultural export; currently almost half the U.S. crop is sent abroad. This trade is controlled by a handful of powerful international grain companies. The expansion of U.S. (and Argentine) soy exports for human consumption is, however, hampered by concern in Europe (and to a lesser extent Japan) over the safety of GM soy; Brazilian soy is often preferred in these markets. Meanwhile, U.S. soy is making major inroads in the Chinese market, particularly with the entry of China into the World Trade Organization.
Processing Soy for Different Cuisines
Processing whole soy. In Asia, soy is prepared in many forms. Immature soybeans simmered in their pods (Japanese edamame ) and sprouts from soybeans germinated in darkness are two vegetable uses. Soymilk is made by adding water to the beans, grinding and heating them, and filtering out the "milk"; in recent decades it has become quite popular in parts of Asia as a noncarbonated soft drink. Yuba is the thin protein film that forms on the surface of hot soymilk; skimmed off and sold in sheets, it is a delicacy in China and Japan. Tofu is made by curdling hot soymilk with a salt or acid coagulant and then pressing the whey out of the curd. Subsequent processing of tofu can include freezing, freeze-drying, deep-frying, or grilling, yielding different textures, flavors, and nutrient profiles. Okara is the pulp that remains after filtration of soymilk. It can be pickled or cooked with meat in stews. Soynuts are whole roasted soybeans consumed as a snack; when ground into a powder, they are used in pastry-making (China, Japan) or eaten with rice (Japan, Indonesia).
Asian societies have also developed many fermented soy products, including fermented tofu (sufu, or "Chinese cheese") and fermented okara. Fermentation increases soy's digestibility, preserves soy for long periods, and, crucially, provides flavoring to stimulate the appetite. Many fermentation processes use Aspergillus fungi, salt-loving yeasts, and lactic acid bacteria. Products include soy paste fermented with or without wheat, barley, or rice (for example, jiang in China; red, white, yellow, or brown miso in Japan); soy sauce, which is made from soy and wheat (either by fermentation or chemically); fermented soy nuggets ("salted black beans"); tempeh, an Indonesian soy cake fermented with Rhizopus mold, served as a main dish, and—when prepared in the traditional manner—often high in vitamin B12 from bacteria exposure during processing; and natto, a sweet, slippery, bacteria–fermented Japanese soybean dish served with soy sauce, mustard, and rice for breakfast or dinner.
In North America there is a small but growing market for soy products. Among those made from whole soybeans, the popularity of flavored soymilks and tofu is complemented by the marketing to vegetarians and health-conscious consumers of Western-style soyfoods such as soy yogurt, frozen soy desserts, and (unfermented) imitation cheese made from soy. In addition, full-fat soy flour is widely used commercially to bleach wheat flour and to condition doughs for Western-style breads.
Processing soy oil. Oil is extracted from soybeans either via chemical solvents such as hexane (the modern technique usually employed in developed countries) or by screw press (a lower-yield technique used at small extraction plants worldwide). Large processors refine the oil using techniques developed beginning in the 1940s. The removal of lecithin (itself used in many food applications—for instance as an emulsifier in chocolates) and other impurities is followed by bleaching and deodorization. The oil is then ready for use in salads and for home cooking. If hydrogenation is performed to enhance solidity and shelf life, soy oil can be blended with other oils to make margarine stock or shortening, including shortening for commercial deep-fat frying. Soy oil is also widely used in American prepared salad dressings and mayonnaises. Indeed, in the United States soy is by far the most commonly used oil in each of these applications. It is becoming increasingly popular worldwide because of its cheap price and high quality.
Processing defatted soy protein. Use of defatted soy protein has gone hand in hand with the development of large-scale hexane extraction of oil from the beans. Hexane, an organic solvent, dissolves the oil, thereby separating it from the soy protein. The hexane is then steamed out of the protein. Once desolventized, the protein is suitable for further refinement and processing into food-grade soy flakes, grits, defatted flour, concentrates (containing at least 70 percent protein), and isolates (containing at least 90 percent protein). Such products are used (1) in very small quantities as "functional" ingredients to improve the textures of a vast array of processed foods, including baked goods, soups, whipped toppings, and lunch meats; (2) as meat extenders in dishes for institutions such as schools and the armed forces; (3) as nutrition enhancers in products touted for their health benefits, such as protein-fortified breakfast cereals, weight-loss beverages, and "energy bars"; and (4) as the primary ingredient in dairy and meat substitutes ("analogs"). While some brands of dairy analogs are made directly from whole soybeans, others are made from defatted soy protein ingredients (or both). Those using defatted soy protein include some imitation cheeses, some frozen soy desserts, and soy infant formulas. Americanstyle meat analogs, pioneered by scientists working for Henry Ford and by vegetarian Seventh Day Adventists, include soy burgers, steaks, "chicken," hot dogs, sausage, "bacon" bits, and lunch meats.
National Differences in Amounts of Soy Protein Consumed
Data from the United Nations Food and Agriculture Organization indicate that in 1999, North Koreans derived more daily protein per capita from soy than people in any other country (9.4 grams), followed by the Japanese (8.7 grams), Indonesians (7.2 grams), South Koreans (6.5 grams), and Chinese (5.1 grams). The many thousands of small tofu shops scattered throughout Japan, similar to bakeries in France, illustrate the dietary and cultural importance of soy protein to that society.
The rest of the world for which data are available had much lower rates of consumption in 1999, although some developing countries (for example, Libya, Uganda, Nigeria, and Costa Rica) have significantly increased their consumption in recent years. Average U.S. daily intake during that year was tiny but growing rapidly. Market studies suggest that soyfood sales are currently increasing at a rate of 30 percent per year in the United States.
Research on Soy's Health Benefits
Soy is the only commonly eaten food containing high levels of isoflavones—compounds similar to human estrogen that have hormonelike effects. In the past decade, hundreds of scientific studies have examined the potential of isoflavones and other components of soy to reduce cancer risks, reverse tumor growth, prevent osteoporosis, mitigate unpleasant symptoms of menopause, and decrease the risk of heart disease. Findings in many areas are still equivocal, but results have been promising with regard to prostate cancer and, especially, heart disease. In 1999, the U.S. Food and Drug Administration permitted manufacturers of foods meeting certain criteria to make claims on food labels linking consumption of soy protein to a potentially reduced risk of heart disease.
Ironically, while soy protein holds promise as a disease-fighting food of the future, and although natural, unhydrogenated soy oil has healthful properties, the hundreds of millions of pounds of hydrogenated soy oil used yearly in the United States to deep-fry fast foods contribute to high cholesterol levels and a national epidemic of obesity.
Future Directions for Soy
Many new varieties of soy are being developed, as conventional breeders and biotechnology companies focus on improving soy to benefit not only farmers, but also processors and consumers. Desired characteristics include improved shelf life and flavor of the oil; enhanced functional qualities of the oil for commercial food processing; improved nutritional profile for the oil or the protein; elimination of antinutritive elements and flatulence causing compounds; and reduction of soy's "beany" flavor. The new varieties are in differing stages of development; for some strains, the economic motivator is the improvement of animal feed or even the mitigation of environmental pollution caused by waste from animals fed conventional varieties. But much of the research has potential application to human foods.
Cultivating soybeans as a protein source for human foods is a significantly more efficient way to provide a population with protein than is raising mammals for meat: in the late 1990s, a pig raised in the United States required over three pounds of feed to produce a single pound of meat; a chicken required about two pounds. For this reason, soy has much greater potential than meat to provide critical protein to the world's hungry. The only flesh foods that currently approach soy's efficiency for protein production are farmed fish.
Development workers have labored, with varying degrees of success, to introduce soybeans into the cuisines of protein-deficient populations. For example, the International Soybean Program (INTSOY) of the University of Illinois has worked extensively in Egypt, the U.S. Peace Corps has introduced soyfoods in Malawi, and the Mennonite Central Committee has had a long-term soyfoods project in Bangladesh. Since according to United Nations estimates world population will grow by some four billion in the twenty-first century, such efforts will surely increase.
See also China ; Dairy Products ; Genetic Engineering ;Japan: Traditional Japanese Cuisine ; Vegetarianism .
Carter, T. E., Jr., and S. Shanmugasundaram. "Vegetable Soybean (Glycine)." In Pulses and Vegetable, edited by J. T. Williams. New York: Chapman & Hall, 1993. Discusses soy, including such agronomic characteristics as photoperiodicity.
Du Bois, Christine M. "A Specific Legume Case: History of Soy and Soy Protein Products in the USA." Presentation for the Johns Hopkins University Center for a Livable Future's "Dietary Protein: Options for the Future" conference, 2001. Published online with references and bibliography available at http://www.jhsph.edu/environment/CLF_conferences/Dietary_Feb01.html.
Food and Agriculture Organization of the United Nations. www.fao.org. "Food Balance Sheets" indicating consumption levels can be found in the "Statistical Databases" section available at http://apps.fao.org/.
Huang, Hsing-Tsung. Fermentations and Food Science. Volume 6, Part 5 of Science and Civilisation in China, edited by Joseph Needham. Cambridge, U.K.: Cambridge University Press, 2000. This volume contains 86 pages on the history of soyfoods in China, drawing on literary texts, archaeology, and comparisons with present-day techniques.
Hymowitz, Theodore. "On the Domestication of the Soybean." Economic Botany 24 (1970): 408–421. Uses genetic data, literary sources, and archaeology to trace the history of soy's domestication. Available online at http://www.nsrl.uiuc.edu/GeneralInfo/historybeans.html.
Hymowitz, Theodore, and C. A. Newell. "Taxonomy of the Genus Glycine, Domestication and Uses of Soybeans." Economic Botany 35(3) (1981): 272–288. Covers history of taxonomic research and deliberations, domestication and diffusion of soybeans, and food uses in Asia and the West.
Johnson, L A., D. J. Myers, and D. J. Burden. "Soy Protein's History, Prospects in Food, Feed." International News on Fats, Oils, and Related Materials 3(4) (1992): 429–444. History of how soy protein has been used in the West.
Liu, KeShun. Soybeans: Chemistry, Technology, and Utilization. New York: Chapman & Hall, 1997. Covers agronomy; marketing; biochemistry; nutrition and health benefits; storage; preparation of Asian and Western soyfoods; genetic engineering.
Mintz, Sidney W., and Chee Beng Tan. "Bean-curd Consumption in Hong Kong." Ethnology 40(2) (2001): 113–128. Ethnographic survey. Details types of bean curd and related products, their production and retailing, and consumption patterns.
Shurtleff, William, and Akiko Aoyagi. The Book of Tofu. New York: Ballantine Books, 1979. Revised edition. Covers history, cultural importance, processing techniques, and recipes for tofu, okara, soymilk, and yuba.
Soya & Oilseed Bluebook. Bar Harbor, Maine: Soyatech, Inc., 2000. Annual directory of companies in soy and other oilseed industries.
Warnken, Philip F. The Development and Growth of the Soybean Industry in Brazil. Ames, Iowa: Iowa State University Press, 1999. Covers place of soy in the overall economy, production trends and programs, and future directions.
World Soybean Research Conference VI Proceedings. Chicago, Ill.: University of Illinois, Urbana–Champaign and Soybean Research & Development Council, 1999. Compiled by Harold E. Kauffman. Covers the state of soybean industries worldwide; biotechnology; breeding; and health issues.
Christine Madeleine Du Bois Sidney W. Mintz
Soy is a general term for products made from soybeans. Soy products include tofu, tempeh, soy oil, natto, miso, soymilk, and edamame.
Soybeans are the most widely used beans in the world. They are a good source of protein and contain no cholesterol. Soy is a complete protein. It contains all the essential amino acids that the body needs, and in this sense is different from most vegetable proteins and nutritionally equivalent to animal protein. Unlike animal protein, soy contains no cholesterol and is low in saturated fat. Soy is a heart-healthy choice and has met the United States Food and Drug Administration (FDA) requirements to make that claim on certain soy product labels.
Soy is believed to promote cardiovascular health, but many other health claims are also made for soy. Some of these claims remain unsubstantiated, are under review, or are in dispute. These health claims include that soy:
- promotes weight loss
- helps prevent certain cancers
- helps slow bone loss
Soybeans are the seeds of the plant Glycine max. This plant is native to China, where it has been cultivated
|Soy sources||Amount of soy protein|
|1 cup (8 ounces) soymilk||10 grams|
|4 ounces tofu||13 grams|
|1 soy burger||10–12 grams|
|1 soy protein bar||14–gram average|
|1 soy sausage link||6 grams|
|¼ cup roasted soy nuts||18–20 grams|
(Illustration by GGS Information Services/Thomson Gale.)
for about 13,000 years. From China, soybeans gradually spread to other areas of Asia, where soy is now a major part of the diet of millions of people. Intense breeding has produced a number of variants (cultivars) of the original plant, some which have a higher oil content and others which have a higher protein content. Soybeans may be green, yellow, brown, or black in color, but all variations are edible.
Soybeans were introduced into the United States in the mid-1700s. George Washington Carver (1864– 1943) experimented with them before he began his famous nutrition research on peanuts. Today the United States is the world’s largest grower of soybeans, producing almost 84 million metric tons in 2005. However, most soybeans grown in the United States are pressed to make soy oil. After the oil is extracted the beans are ground into meal and used as livestock feed.
Soy products are part of the daily diet of many Asians. However, soy has only become readily available in mainstream food stores in the United States since the 1990s. In 1979 the first major company, Vitasoy, introduced soymilk into the United States. Since then, the number of soy products has soared. The Soyfoods Association of North America estimates that sales of soy products in the United States increased from $300 million in 1992 to $3.9 billion in 2004, and sales were expected to continue rising through the end of the decade. Between 2000 and
2006, 2,500 new food products containing soy were introduced to the U.S. market.
Nutritional value of soy
Soy is a nutrient dense food, and it is the least expensive source of complete dietary protein. It is relatively low in calories and contains no cholesterol, saturated fat, or trans–fat. One cup (172 g) of cooked soybeans has about 300 calories and contains the following nutrients. The percentage DV is the percent of the daily requirement that 1 cup of cooked soybeans meets for the average adult.
Amino acid —Molecules that are the basic building blocks of proteins.
Dietary fiber —Also known as roughage or bulk. Insoluble fiber moves through the digestive system almost undigested and gives bulk to stools. Soluble fiber dissolves in water and helps keep stools soft.
Dietary supplement —A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual’s diet with the expectation that it will improve health.
Essential amino acid —An amino acid that is necessary for health but that cannot be made by the body and must be acquired through diet.
Fatty acids —Complex molecules found in fats and oils. Essential fatty acids are fatty acids that the body needs but cannot synthesize. Essential fatty acids are made by plants and must be present in the diet to maintain health.
- protein 28.6 g: 57% DV
- dietary fiber: 10.3 g; 41% DV
- total fat: 15.4 g; calories from fat 139
- molybdenum: 129 mcg; 172% DV
- manganese: 1.4 mg; 71% DV
- iron: 8.8 mg: 49% DV
- vitamin K: 33.0 mg; 41.3 57% DV
- omega-3 fatty acids: 1.03; 41.3 57% DV
- magnesium: 147.9 mg: 37% DV
- vitamin B2 (riboflavin): 0.5 mg: 29 % DV
- potassium: 886 mg: 25% DV
Fresh soybeans can be cooked briefly in boiling water and then eaten, or they can be toasted. Dried beans need to be soaked overnight before cooking and require relatively long cooking times. Soybeans can also be pressed to make soy oil, but the most familiar soy products come from soybeans that are processed in various ways that give them a variety of textures and make them easier to use in cooking. These include:
- Tofu: Tofu is made of cooked, pureed, soybeans that are processed and then formed into soft slabs that must be kept wet until they are used. The slabs are produced with consistencies that vary from very soft or ‘‘silken’’ to firm or extra firm. Other tofu variations include reduced-calorie tofu and tofu fortified with calcium. Tofu is used to make cheese substitutes, blended into smoothies, and stir fried. It has a bland taste and tends to take on the flavors of the foods it is cooked with.
- Tempeh: Tempeh is made from partially cooked soybeans that are then fermented in a controlled environment. Tempeh is chewier than tofu and is often used as a meat substitute.
- Miso: Miso is a fermented soybean paste that is used as a soup base and for seasoning.
- Soymilk: Soymilk is a soy beverage made by grinding soybeans and mixing them with water. Soymilk can be flavored (chocolate, vanilla, coffee) or sold plain. Some soymilk is fortified with calcium. People who are lactose intolerant often use soymilk as a substitute for cow’s milk, and soy is also used in formula for infants who cannot tolerate lactose.
- Soy flour: Soy flour comes from roasted, ground soybeans. It can be used in baked goods, cereals, and many other foods. Soy flour contains more moisture than wheat flour. People with celiac disease who cannot tolerate wheat, barley, or rye products can use soy flour.
- Textured soy protein: This product is used most often as a meat substitute in processed foods such as soy burgers or home-cooked foods such as meat-loaf. It is made by defatting soyflour, which is then compressed into clumps and dehydrated.
The role of soy in health
In October 1999, the FDA decided that well-designed, well-controlled, repeatable research studies had shown that soy was a heart healthy food that could help decrease the risk of developing cardiovascular disease. Since that date, the FDA has allowed products that contained at least 6.25 g of soy per serving to make the following health claim on their label: ‘‘25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.‘‘ This endorsement applies only to complete soy products, not to soy-based dietary supplements. The American Heart Association (AHA) also gave its approval to soy as a food that can reduce the risk of heart disease.
Soy is a food that can also help in weight loss because it can be used as a substitute for higher calorie meat. If soy is substituted for meat on a regular basis, the reduction in calories can be significant. For example:
- A soy burger patty has about 100 fewer calories than an equivalent-sized beef burger patty.
- Two links of soy breakfast sausage have about 90 fewer calories than two links of pork breakfast sausage.
- A soy veggie dog has about 70 fewer calories than a beef hotdog.
Some health controversies about soy center on compounds called isoflavones that are found in abundance in soybeans. These compounds have a chemical structure similar to the female hormone estrogen. Several health effects, both positive and negative, have been attributed to isoflavones. In 2006, the American Heart Association concluded that isoflavones are not the cause of the cholesterol-lowering, heart-healthy properties in soy and that dietary supplements containing soy-derived isoflavones do not have the same cardiovascular benefits as whole soy.
Another claim is that isoflavones can improve bone health in women. This claim appears plausible because of the chemical similarity between isoflavones and estrogen. Estrogen is known to increase the amount of calcium deposited in bones, and the lack of estrogen in post-menopausal women is linked to decreasing estrogen levels. However plausible the connection between bone health and isoflavones in soy may be, studies have produced inconclusive results. As of 2007, any effect that soy may have on bone health appears to be weak. Also, because of their estrogen-like structure, isoflavones from soy have been touted as a dietary supplement that will help prevent symptoms of menopause such as hot flashes. A committee of the AHA that investigated isoflavones found that they had no effect on hot flashes.
A far bigger health question concerns the relationship between isoflavones and cancer. The AHA committee found that despite claims that soy isoflavone supplements can treat and prevent breast, endometrial, and uterine cancer in women and prostate cancer in men, there was no evidence to suggest that this treatment was safe or effective. On the other hand, there was also no evidence that, as some experts have suggested, soy increases the chance of post-menopausal women developing breast cancer. A large number of federally sponsored clinical trials are underway to investigate these and other effects of isoflavones and soy.
Although soy is often thought of as a benign food, some people are allergic to soy.
Soy contains compounds called goitrogens. Goitrogens interfere with the body’s ability to absorb or use iodine . The goitrogens in soy should not cause problems with iodine uptake in healthy people, but people with thyroid deficiencies should discuss with their healthcare provider whether they should limit soy in their diet.
No complications are expected from eating soy products.
One long-term study is underway to investigate the effect of increased concentrations of isoflavones in the blood of children who drink soy formula. The study plans to look for potential effects across a period of about 20 years, so no results are available yet.
GeniSoy Products. The Magic of Soy: Healthy Cooking with Soy Protein Summertown, TN: Book Pub. Co.,2000.
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American Soybean Association. 12125 Woodcrest Executive Drive, Suite 100, St. Louis,MO 63141. Telephone: (800)688-7692.Website: <http://www.amsoy.org>
Soyfoods Association of North America. ‘‘Soy Safety.’’
United States Department of Health and Human Services and the United States Department of Agriculture. ‘‘Dietary Guidelines for Americans 2005.’’ January 12, 2005. <http://www.healthierus.gov/dietaryguidelines>
Whfoods.org. ‘‘Soybeans.’’ World’s Healthiest Foods, undated, accessed April 26, 2007. <http://www.whfoods.com/>
Helen M. Davidson
A member of the legume family, the soybean is rich in omega-3 fatty acids , fiber , folic acid, calcium , magnesium, potassium, and the B vitamins and is also cholesterol free and low in saturated fat . The protein in soybeans is complete, containing all the essential amino acids found in animal sources (4 ounces of tofu [soybean curd] contain the same amount and quality of protein as a similar-size hamburger). For individuals who want to include more plant-based protein in their diet and particularly for those on a vegetarian diet, soy products provide a way to add nonmeat protein to the diet.
Soy and Your Heart
Among the many benefits of soy are the potential for lowering one's risk of heart disease , menopausal bone loss, breast and prostate cancer, and osteoporosis . The results of a 1995 meta-analysis (combining results from separate but related studies) published in the New England Journal of Medicine found that consuming an average of 47 grams of soy protein a day, rather than animal protein, significantly decreased LDL cholesterol in people with moderately elevated or elevated cholesterol levels (low-density lipoproteins (LPLs) are the "bad" type of cholesterol and have been associated with clogged arteries and heart attacks). The study also found that high-density lipoprotein HDL cholesterol (the beneficial, or "good," cholesterol) was not affected by the consumption of soy protein.
Scientists suggest that soy protein and isoflavones are the active substances helping to keep blood vessels flexible and preventing deadly blood clots. Isoflavones are phytochemicals (naturally occurring compounds) found in plants, and they have potentially strong biological activity, meaning they exert a physiological effect, in the body. Phytochemicals give plants their color, flavor, and odor, and they have benefits to the body beyond basic nutrition . The U.S. Food and Drug Administration (FDA) has approved a health claim stating that consuming 25 grams of soy protein per day, along with a diet low in saturated fat and cholesterol, may reduce the risk for heart disease. The FDA also suggests that four servings of soy foods per day can lower LDL cholesterol by 10 percent. To use this claim, a food product must contain 6.25 grams of soy protein per serving. The claim does not include a recommendation for isoflavone level, which remains an issue of debate. The 25 gram recommendation applies to all ages.
|Soy sources||Amount of soy protein|
|1 cup (8 ounces) soymilk||10 grams|
|4 ounces tofu||13 grams|
|1 soy burger||10–12 grams|
|1 soy protein bar||14–gram average|
|1 soy sausage link||6 grams|
|¼ cup roasted soy nuts||18–20 grams|
Many of today's common diseases are not diseases of aging, but of lifestyle , and they can take twenty to thirty years to develop. Typically, when soy protein replaces animal protein, the consumption of saturated fat and cholesterol goes down. About 40 percent of the soybean's calories come from fat , with the majority (54 %) being unsaturated. The polyunsaturated fat in the soybean includes omega-3 fatty acids, which are not frequently found in plants.
Soy and Cancer
Soybeans and soy foods in the diet may provide strong anticancer activity because they are natural sources of isoflavones. A specific isoflavone called genistein, which is found is soy, appears to help block tumor-cell growth. Current studies indicate that consuming soy may reduce the risk of developing prostate cancer, while isoflavone supplements may help physicians stabilize prostate cancer by decreasing the prostate-specific antigen (PSA) level used to measure how well the cancer is being controlled.
There has been much debate and disagreement about soy consumption and its role in breast cancer. Similar in chemical structure to estrogen , isoflavones are in fact, weak estrogens, and they may act as such in the body. Hormone replacement therapy (HRT) has been shown to increase breast density, a factor in breast-cancer risk (as breast density increases, so does the risk for breast cancer), while recent soy studies have found that soy use in both premenopausal and postmenopausal women did not affect breast density.
Soy and Menopause
The popularity of soy-based foods is also due to their potential for reducing the symptoms of menopause. In a study published in Obstetrics and Gynecology, researchers found that women who consumed 60 grams of isolated soy protein daily reported a reduction in moderate to severe hot flashes. Other studies have contradicted this finding, however, Japanese women, who typically have a soy-rich diet, do experience a lower incidence of most post-menopausal symptoms than women in Western countries, including hot flashes, hormone-related cancers, and osteoporosis.
Soy and Osteoporosis
Another area with conflicting studies is the link between soy and osteoporosis. One method for determining your bone health and changes in bone density over time is calcium metabolism (a process where a substance, necessary for life, is synthesized or broken down). For bone density to increase, more calcium must be kept in the bones. This retention is measured by tests that look at calcium absorption versus calcium loss as measured in the urine. In studies that have compared a soy diet to a calcium/whey diet, calcium loss through the urine was much lower on the soy diet. Some researchers suggest that the amino-acid content of soy protein, as compared to that of animal protein, is the reason for less calcium loss in the urine.
The versatile soybean remains a popular food choice, and adding soy to the diet is one component of a healthful eating program. Even the soybean pod itself, called edamame, is sometimes eaten as a snack food.
see also Functional Foods; Legumes; Meat Analogs; Plant-Based Diets; Vegetarianism.
Anderson, James W., et al. (1995). "Meta-Analysis of the Effects of Soy Protein Intake on Serum Lipids." New England Journal of Medicine 333:276–82.
Albertazzi P., et al. (1998). "The Effect of Dietary Soy Supplementation on Hot Flashes." Obstetrics and Gynecology 91:6–11.
Messina, Mark (2002). "Symposium Highlights Significant Research On Soy and Human Health." The Soy Connection, Winter. Chesterfield, MO: United Soybean Board. Also available from <http://www.talksoy.com>
Stevens and Associates (2002). "The U.S. Soyfoods Directory." Available from <http://www.soyfoods.com>
United States Department of Agriculture, Agricultural Research Service (2002). "USDA-Iowa State University Database on the Isoflavone Content of Foods." Available from <http://www.nal.usda.gov/fnic/foodcomp/Data/isoflav/isoflav.html>