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The soybean (U.S.) or soya bean (UK) (Glycine max) is a species of legume native to East Asia. The plant is classed as an oilseed rather than a pulse. It is an annual plant that has been used in China for 5,000 years as a food and a component of drugs. Soy contains significant amounts of all the essential amino acids for humans, and so is a good source of protein. Soybeans are the primary ingredient in many processed foods, including dairy product substitutes.
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The soybean (U.S.) or soya bean (UK) (Glycine max) is a species of legume native to East Asia. The plant is classed as an oilseed rather than a pulse. It is an annual plant that has been used in China for 5,000 years as a food and a component of drugs. Soy contains significant amounts of all the essential amino acids for humans, and so is a good source of protein. Soybeans are the primary ingredient in many processed foods, including dairy product substitutes. The plant is sometimes referred to as greater bean or edamame, though the later is more commonly used in English when referring to a specific dish.
The English word soy is derived from the Japanese pronunciation of ?? (????, shoyu), the Japanese word for Soya sauce; soya comes from the Dutch adaptation of the same word.
Soybeans are an important source of vegetable oil, protein, and fertilizer world wide. Soy products are the main ingredients in many meat and dairy substitutes. They are also used in to make soy sauce, and the oil is used in many industrial applications. The main producers of soy are the United States, Brazil, Argentina, and China. The beans contain significant amounts of alpha-linolenic acid, omega-6 fatty acid, and the isoflavones genistein and daidzein.
Classification
The genus name Glycine was originally introduced by Linnaeus (1737) in his first edition of Genera Plantarum. The word glycine is derived from the Greek-glykys (sweet) and very likely refers to the sweetness of the pear-shaped (apios in Greek) edible tubers produced by the native North American twining or climbing herbaceous legume, Glycine apios, now known as Apios americana. The cultivated soybean first appeared in the Species Plantarum, Linnaeus, under the name Phaseolus max L. The combination, Glycine max(L.) Merr., as proposed by Merrill in 1917, has become the valid name for this useful plant.
Like some other crops of long domestication, the relationship of the modern soy bean to wild-growing species can no longer be traced with any degree of certainty. It is a cultural variety with a very large number of cultivars.
The genus Glycine Wild. is divided into two subgenera (species), Glycine and Soja. The subgenus Soja (Moench) includes the cultivated soybean, G. max (L.) Merrill, and the wild soybean, G. soja Sieb.& Zucc. Both species are annual. The soybean grows only under cultivation while G. soja grows wild in China, Japan, Korea, Taiwan and Russia. Glycine soja is the wild ancestor of the soybean: the wild progenitor. At present, the subgenus Glycine consists of at least 16 wild perennial species: for example, Glycine canescens, and G. tomentella Hayata found in Australia, and Papua New Guinea.
Description and physical characteristics
Soy varies in growth, habit, and height. It may grow prostrate, not higher than 20 cm (7.8 inches), or grow up to 2 meters (6.5 feet) high.
The pods, stems, and leaves are covered with fine brown or gray hairs. The leaves are trifoliolate, having 3 to 4 leaflets per leaf, and the leaflets are 6–15 cm (2–6 inches) long and 2–7 cm (1–3 inches) broad. The leaves fall before the seeds are mature. The big, inconspicuous, self-fertile flowers are borne in the axil of the leaf and are white, pink or purple.
The fruit is a hairy pod that grows in clusters of 3–5, each pod is 3–8 cm long(1–3 inches) and usually contains 2–4 (rarely more) seeds 5–11 mm in diameter.
Soybeans occur in various sizes, and in many hull or seed coat colors, including black, brown, blue, yellow, green and mottled. The hull of the mature bean is hard, water resistant, and protects the cotyledon and hypocotyl (or "germ") from damage. If the seed coat is cracked, the seed will not germinate. The scar, visible on the seed coat, is called the hilum (colors include black, brown, buff, gray and yellow) and at one end of the hilum is the micropyle, or small opening in the seed coat which can allow the absorption of water for sprouting.
Remarkably, seeds such as soybeans containing very high levels of protein can undergo desiccation yet survive and revive after water absorption. A. Carl Leopold, son of Aldo Leopold, began studying this capability at the Boyce Thompson Institute for Plant Research at Cornell University in the mid 1980s. He found soybeans and corn to have a range of soluble carbohydrates protecting the seed's cell viability. Patents were awarded to him in the early 1990s on techniques for protecting "biological membranes" and proteins in the dry state. Compare to tardigrades.
Chemical composition of the seed
Together, oil and protein content account for about 60% of dry soybeans by weight; protein at 40% and oil at 20%. The remainder consists of 35% carbohydrate and about 5% ash. Soybean cultivars comprise approximately 8% seed coat or hull, 90% cotyledons and 2% hypocotyl axis or germ.
The majority of soy protein is a relatively heat-stable storage protein. This heat stability enables soy food products requiring high temperature cooking, such as tofu, soymilk and textured vegetable protein (soy flour) to be made.
The principal soluble carbohydrates, saccharides, of mature soybeans are the disaccharide sucrose (range 2.5–8.2%), the trisaccharide raffinose (0.1–1.0%) composed of one sucrose molecule connected to one molecule of galactose, and the tetrasaccharide stachyose (1.4 to 4.1%) composed of one sucrose connected to two molecules of galactose. While the oligosaccharides raffinose and stachyose protect the viability of the soy bean seed from desiccation (see above section on physical characteristics) they are not digestible sugars and therefore contribute to flatulence and abdominal discomfort in humans and other monogastric animals; compare to the disaccharide trehalose. Undigested oligosaccharides are broken down in the intestine by native microbes producing gases such as carbon dioxide, hydrogen, methane, etc.
Since soluble soy carbohydrates are found in the whey and are broken down during fermentation, soy concentrate, soy protein isolates, tofu, soy sauce, and sprouted soy beans are without flatus activity. On the other hand, there may be some beneficial effects to ingesting oligosaccharides such as raffinose and stachyose, namely, encouraging indigenous bifidobacteria in the colon against putrefactive bacteria.
The insoluble carbohydrates in soybeans consist of the complex polysaccharides cellulose, hemicellulose, and pectin. The majority of soybean carbohydrates can be classed as belonging to dietary fiber.
Nutrition
Soybeans are considered by many agencies, including the US Food and Drug Administration, to be a source of complete protein. A complete protein is one that contains significant amounts of all the essential amino acids that must be provided to the human body because of the body's inability to synthesize them. For this reason, soy is a good source of protein, amongst many others, for many vegetarians and vegans or for people who cannot afford meat.
According to the FDA, "Soy protein products can be good substitutes for animal products because, unlike some other beans, soy offers a "complete" protein profile. Soybeans contain all the amino acids essential to human nutrition, which must be supplied in the diet because they cannot be synthesized by the human body. Soy protein products can replace animal-based foods--which also have complete proteins but tend to contain more fat, especially saturated fat--without requiring major adjustments elsewhere in the diet."
However, as with any dietary health claim, there are opposing viewpoints on the health benefits of soybeans.
The gold standard for measuring protein quality, since 1990, is the Protein Digestibility Corrected Amino Acid Score (PDCAAS) and by this criterion soy protein is the nutritional equivalent of meat and eggs for human growth and health. Soybean protein isolate has a Biological Value of 74, whole soybeans 96, soybean milk 91, and eggs 97.
Soy protein is essentially identical to that of other legume pulses seeds. Moreover, it has the highest yield per square meter of growing area, and is the least expensive source of dietary protein.
Consumption of soy may also reduce the risk of colon cancer, possibly due to the presence of sphingolipids.
Cultivation
Soybeans are an important global crop, providing oil and protein. The bulk of the crop is solvent-extracted for vegetable oil and then defatted Soymeal is used for animal feed. A small proportion of the crop is consumed directly by humans. Soybean products do appear in a large variety of processed foods.
During World War II, soybeans became important in both North America and Europe chiefly as substitutes for other protein foods and as a source of edible oil. It was during World War II that the soybean was discovered as fertilizer by the Department of Agriculture. In the 1960-1 Dillion round of the GATT the United States secured tariff-free access for it's soybeans in the European market. In the 1960s the United States exported over 90% of the worlds soybeans. .. . The soybean is now a leading crop in the United States. Brazil, Argentina, and Paraguay also are significant soybean-exporting nations.
Cultivation is successful in climates with hot summers, with optimum growing conditions in mean temperatures of 20 °C to 30 °C (68°F to 86°F); temperatures of below 20 °C and over 40 °C (68 °F, 104 °F) retard growth significantly. They can grow in a wide range of soils, with optimum growth in moist alluvial soils with a good organic content. Soybeans, like most legumes, perform nitrogen fixation by establishing a symbiotic relationship with the bacterium Bradyrhizobium japonicum (syn. Rhizobium japonicum; Jordan 1982). However, for best results an inoculum of the correct strain of bacteria should be mixed with the Soy bean (or any legume) seed before planting. Modern crop cultivars generally reach a height of around 1 m (3 ft), and take 80–120 days from sowing to harvesting.
Soybeans are native to east Asia but only 45 percent of soybean production is located there. The other 55 percent of production is in the Americas. The U.S. produced 75 million tons of soybeans in 2000, of which more than one-third was exported. Other leading producers are Brazil, Argentina, Paraguay, China, and India.
Environmental groups, such as Greenpeace and the WWF, have reported that both soybean cultivation and the probability of increased soybean cultivation in Brazil, has destroyed huge areas of Amazon rainforest and is encouraging further deforestation.
Growing soy also requires the use of harmful pesticides and herbicides, while alternative sources of plant protein such as hemp do not.
American soil scientist Dr. Andrew McClung, who first showed that the ecologically biodiverse savannah of the Cerrado region of Brazil could grow profitable soybeans, was awarded the 2006 World Food Prize on October 19, 2006.
The first research on soybeans in the United States was conducted by George Washington Carver at Tuskegee, Alabama, but he decided it was too exotic a crop for the poor black farmers of the South so he turned his attention to peanuts.
History
Soybeans were a crucial crop in eastern Asia long before written records, and they remain a major crop in China, Japan, and Korea. Prior to fermented products such as Soy sauce, tempeh, natto, and miso, soy was considered sacred for its use in crop rotation as a method of fixing nitrogen. The plants would be plowed under to clear the field for food crops. Soy was first introduced to Europe in the early 1700s and what is now the United States in 1765, where it was first grown for hay. Benjamin Franklin wrote a letter in 1770 mentioning sending soybeans home from England. Soybeans did not become an important crop outside of Asia until about 1910. In America, soy was considered an industrial product only and not used as a food prior to the 1920s. Soy was introduced to Africa from China in the late 19th Century and is now widespread across the continent.
Asia
The origins of the soybean plant are obscure, but many botanists believe it to have derived from Glycine ussuriensis, a legume native to central China. The soybean has been used in China for 5,000 years as a food and a component of drugs. According to the ancient Chinese, in 2853 BC the legendary Emperor Shennong of China proclaimed that five plants were sacred: soybeans, rice, wheat, barley, and millet. Cultivation of soybeans was long confined chiefly to China, but gradually spread to other countries.
The earliest preserved soybeans were found in archaeological sites in Korea. Radiocarbon dating of soybean samples recovered through flotation during excavations at the Early Mumun period Okbang site in Korea indicates that soybean was cultivated as a food crop in ca. 1000–900 BC.
From about the first century AD to the Age of Discovery (15-16th century), soybeans were introduced into several countries such as Japan, Indonesia, the Philippines, Vietnam, Thailand, Malaysia, Burma, Taiwan, Nepal and India. This spread was due to the establishment of sea and land trade routes. The best current evidence on the Japanese Archipelago suggests that soybean cultivation occurred in the early Yayoi period. The earliest Japanese textual reference to the soybean is in the classic Kojiki (Records of Ancient Matters) which was completed in 712 AD.
Many people have claimed that soybeans in Asia were historically only used after a fermentation process, which lowers the high phytoestrogens content found in the raw plant. However, terms similar to "soy milk" have been in use since 82 AD , and there is evidence of tofu consumption that dates to 220.
United States
Soy took on a very important role in the United States after World War I. During the Great Depression, the drought stricken (Dust Bowl) regions of the United States were able to use soy to regenerate their soil because of its nitrogen-fixing properties. Farms were increasing production in order to meet with government demands, and Henry Ford was a great leader of the soybean industry.
In 1932-33 the Ford Motor Company spent approximately $1,250,000 on soybean research. By 1935 every Ford car had soy involved in its manufacture. For example, the soybean oil was used to paint the automobiles as well as fluid for shock absorbers. Ford scientists had developed a fiber from soy protein which was wool-like, very soft, and chosen to be used for the making of suits, felt hats, and overcoats. Ford himself wore a suit made entirely from soybeans, he was even said to have had dinner parties with nothing but soybean based foods on the menu. Ford's involvement with the soybean opened many doors for agriculture and industry to be linked more strongly than it ever had before.
Henry Ford promoted the soybean, helping to develop uses for it both in food and in industrial products, even demonstrating auto body panels made of soy-based plastics. Ford's interest led to two bushels of soybeans being used in each Ford car as well as products like the first commercial soy milk, ice cream and all-vegetable non-dairy whipped topping. The Ford development of so-called soy-based plastics was based on the addition of soybean flour and wood flour to phenolformaldehyde plastics.
In 1931, Ford hired chemists Robert Boyer and Frank Calvert to produce artificial silk. They succeeded in making a textile fiber of spun soy protein fibers, hardened or tanned in a formaldehyde bath which was given the name Azlon by the Federal Trade Commission. Pilot production of Azlon reached 5000 pounds per day in 1940, but never reached the commercial market.
Soybean diseases
Genetic modification
Soybeans are one of the "biotech food" crops that have been genetically modified, and genetically modified soybeans are being used in an increasing number of products. In 1995 Monsanto introduced Roundup Ready (RR) soybeans that have been genetically modified to be resistant to the herbicide Roundup through substitution of the Agrobacterium sp. (strain CP4) gene EPSP (5-enolpyruvyl shikimic acid-3-phosphate) synthase. The substituted version is not sensitive to glyphosate.
In 1997, about 8% of all soybeans cultivated for the commercial market in the United States were genetically modified. In 2006, the figure was 89%. As with other "Roundup Ready" crops, concern is expressed over damage to biodiversity. However, the RR gene has been bred into so many different soybean cultivars that the genetic modification itself has not resulted in any decline of genetic diversity, as demonstrated by a 2003 study on genetic diversity.
The widespread use of such types of GM soybeans in the Americas has caused problems with exports to some regions. GM crops require extensive certification before they can be legally imported into the European Union, where there is considerable supplier and consumer reluctance to use GM products for consumer or animal use. Difficulties with coexistence and subsequent traces of cross-contamination of non-GM stocks have caused shipments to be rejected and have put a premium on non-GM soy.
Uses
Soybeans can be broadly classified as "vegetable" (garden) or field (oil) types. Vegetable types cook more easily, have a mild nutty flavor, better texture, are larger in size, higher in protein, and lower in oil than field types. Tofu and soymilk producers prefer the higher protein cultivars bred from vegetable soybeans originally brought to the United States in the late 1930s. The "garden" cultivars are generally not suitable for mechanical combine harvesting because they have a tendency for the pods to shatter on reaching maturity.
Among the legumes, the soybean, also classed as an oilseed, is pre-eminent for its high (38–45%) protein content as well as its high (20%) oil content. Soybeans are the leading agricultural export in the United States. The bulk of the soybean crop is grown for oil production, with the high-protein defatted and "toasted" soy meal used as livestock feed. A smaller percentage of soybeans are used directly for human consumption.
Immature soybeans may be boiled whole in their green pod and served with salt, under the Japanese name edamame . Because of the proclaimed health benefits of soy, edamame has been featured as an ideal snack alternative in fitness and healthy living magazines such as Real Simple. Edamame is sold in the frozen vegetable section at some larger grocery stores, and as ready-to-eat snackfood in many Asian delis.
In China, Japan, and Korea the bean and products made from the bean are a popular part of the diet. The Chinese invented tofu, and also made use of several varieties of soybean paste as seasonings. Japanese foods made from soya include miso, natto, kinako and edamame. In Korean cuisine, soybean sprouts, called kongnamul are also used in a variety of dishes such as doenjang, cheonggukjang and ganjang.
The beans can be processed in a variety of ways. Common forms of soy (or soya) include soy meal, soy flour, soy milk, tofu, textured vegetable protein (TVP, which is made into a wide variety of vegetarian foods, some of them intended to imitate meat), tempeh, soy lecithin and soybean oil. Soybeans are also the primary ingredient involved in the production of soy sauce (or shoyu).
Archer Daniels Midland (ADM) is among the largest processors of soybeans and soy products. ADM along with Dow Chemical Company, DuPont and Monsanto support the industry trade associations United Soybean Board (USB) and Soyfoods Association of North America (SANA). These trade associations have increased the consumption of soy products dramatically in recent years.
Oil
In processing soybeans for oil extraction and subsequent soy flour production, selection of high quality, sound, clean, dehulled yellow soybeans are very important. Soybeans having a dark colored seed coat, or even beans with a dark hilum will inadvertently leave dark specks in the flour, and are undesirable for use in commercial food products. All commercial soybeans in the United States are yellow or yellow brown.
To produce soybean oil, the soybeans are cracked, adjusted for moisture content, rolled into flakes and solvent-extracted with commercial hexane. The oil is then refined, blended for different applications, and sometimes hydrogenated. Soybean oils, both liquid and partially hydrogenated, are exported abroad, sold as "vegetable oil," or end up in a wide variety of processed foods. The remaining soybean husks are used mainly as animal feed.
The major unsaturated fatty acids in soybean oil triglycerides are 7% linolenic acid (C18:3); 51% linoleic acid (C-18:2); and 23% oleic acid(C-18:1). It also contains the saturated fatty acids 4% stearic acid and 10% palmitic acid.
Soybean oil has a relatively high proportion, 7–10%, of oxidation prone linolenic acid, which is an undesirable property for continuous service, such as in a restaurant. In the early nineties, Iowa State University developed soybean oil with 1% linolenic acid in the oil. Three companies, Monsanto, DuPont/Bunge, and Asoyia in 2004 introduced low linolenic, (C18:3; cis-9, cis-12, cis-15 octadecatrienoic acid) Roundup Ready soybeans. In the past, hydrogenation was used to reduce the unsaturation in linolenic acid, but this produced the unnatural trans-fatty acid configuration, whereas in nature the configuration is cis (see trans fat). This external from North Dakota State University compares soybean oil fatty acid content with other oils.
In the 2002–2003 growing season, 30.6 million tons of soybean oil were produced worldwide, constituting about half of worldwide edible vegetable oil production, and thirty percent of all fats and oils produced, including animal fats and oils derived from tropical plants.
While soybean oil has no direct insect repellent activity, it is used as a fixative to extend the short duration of action of essential oils such as geranium oil in several commercial products.
Meal
Soybean meal, the material remaining after solvent extraction of soybean flakes, with a 50% soy protein content, toasted (a misnomer because the heat treatment is with moist steam) and ground in a hammer mill, provided the energy for the American production method, beginning in the 1930s, of growing farm animals such as poultry and swine on an industrial scale; and more recently the aquaculture of catfish.
Flour
Soy flour refers to defatted soybeans where special care was taken during desolventizing (not toasted) in order to minimize denaturation of the protein to retain a high Nitrogen Solubility Index (NSI), for uses such as extruder texturizing (TVP). It is the starting material for production of soy concentrate and soy protein isolate.
- Defatted soy flour is obtained from solvent extracted flakes, and contains less than 1% oil.
- Full-fat soy flour is made from unextracted, dehulled beans, and contains about 18% to 20% oil. Due to its high oil content a specialized Alpine Fine Impact Mill must be used for grinding rather than the more common hammer mill.
- Low-fat soy flour is made by adding back some oil to defatted soy flour. The lipid content varies according to specifications, usually between 4.5% and 9%.
- High-fat soy flour can also be produced by adding back soybean oil to defatted flour at the level of 15%.
- Lecithinated soy flour is made by adding soybean lecithin to defatted, low-fat or high-fat soy flours to increase their dispersibility and impart emulsifying properties. The lecithin content varies up to 15%.
Infant formula
Infant formulas based on soy (SBIF) are used by lactose-intolerant babies and for babies that are allergic to cow milk proteins. The formulas are sold in powdered, ready-to-feed, or concentrated liquid forms.
Some reviews express the opinion that more research is needed to answer the question of what effect the phytoestrogens contained in soy formula may have on infants, but did not find any adverse effects. Diverse studies conclude there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy-based infant formula. One of these studies, published at the Journal of Nutrition, concludes that:
...there is no clinical concerns with respect to nutritional adequacy, sexual development, neurobehavioral development, immune development, or thyroid disease. SBIFs provide complete nutrition that adequately supports normal infant growth and development. FDA has accepted SBIFs as safe for use as the sole source of nutrition.
Meat and dairy substitutes
Soybeans can be processed to produce a texture and appearance similar to many other foods. For example, soybeans are the primary ingredient in many dairy product substitutes (e.g., soy milk, margarine, soy ice cream, soy yogurt, soy cheese and soy cream cheese) and meat substitutes (e.g. veggie burgers). These substitutes are readily available in most supermarkets. Although soy milk does not naturally contain significant amounts of digestable calcium (the high calcium content of soybeans is bound to the insoluble constituents and remains in the soy pulp), many manufacturers of soy milk sell calcium-enriched products as well.
Soy products also are used as a low cost filler in meat and poultry products. Food service, retail and institutional (primarily school lunch and correctional) facilities regularly use such "extended" products. Extension may result diminished flavor, but fat and cholesterol are reduced. Vitamin and mineral fortification can be used to make soy products nutritionally equivalent to animal protein; the protein quality is already roughly equivalent.
Other products
Soybeans are the bean used in Chinese fermented black beans, douchi, not the sometimes confused black turtle beans.
Soybeans are also used in industrial products including oils, soap, cosmetics, resins, plastics, inks, crayons, solvents, and clothing. Soybean oil is the primary source of biodiesel in the United States, accounting for 80% of domestic biodiesel production. Soybeans have also been used since 2001 as fermenting stock in the manufacture of a brand of vodka.
Today, very high quality textile fibers are made commercially from "okara" (soy pulp), a byproduct of tofu production.
Soybean meal
Soybean meal is a byproduct of milling soybeans and used in lower end dog foods.
Role of soyfoods in disease prevention
Omega-3 fatty acids
Omega-3 fatty acids, for example, alpha-linolenic acid C18-3, all cis, 9,12,15 octadecatrienoic acid (where the omega-3 refers to carbon number 3 counting from the hydrocarbon tail whereas C-15 refers to carbon number 15 counting from the carboxyl acid head) are special fat components that benefit many body functions. However, the effects which are beneficial to health are associated mainly with the longer-chain, more unsaturated fatty acids eicosapentaenoic (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) found in fish oil and oily fish. For instance, EPA and DHA, inhibit blood clotting, while there is no evidence that alpha-linolenic acid (aLNA) can do this. Soybean oil is one of the few common vegetable oils that contains a significant amount of aLNA; others include canola, walnut, hemp, and flax. However, soybean oil does not contain EPA or DHA. Soybean oil does contain significantly greater amount of omega-6 fatty acids in the oil: 100g of soybean oil contains 7g of omega-3 fatty acids to 51g of omega-6: a ratio of 1:7. Flaxseed, in comparison, has an omega-3:omega-6 ratio of 3:1.
Isoflavones
Soybeans also contain the isoflavones genistein and daidzein, types of phytoestrogen, that are considered by some nutritionists and physicians to be useful in the prevention of cancer and by others to be carcinogenic and endocrine disruptive. Soy's content of isoflavones are as much as 3 mg/g dry weight. Isoflavones are polyphenol compounds, produced primarily by beans and other legumes, including peanuts and chickpeas. Isoflavones are closely related to the antioxidant flavonoids found in other plants, vegetables and flowers. Isoflavones such as genistein and daidzein are found in only some plant families, because most plants do not have an enzyme, chalcone isomerase which converts a flavone precursor into an isoflavone.
In contradiction to well known benefits of isoflavones, Genistein acts as an oxidant (stimulating nitrate synthesis), as well as it blocks formation of new blood vessels (antiangiogenic effects). Some studies show Genistein to act as inhibitor of the activity of substances in the body that regulate cell division and cell survival (growth factors).
Claims of cholesterol reduction
The dramatic increase in soyfood sales is largely credited to the Food and Drug Administration's (FDA) approval of soy as an official cholesterol-lowering food, along with other heart and health benefits. A 2001 literature review argued that these health benefits were poorly supported by the available evidence, and noted that disturbing data on soy's effect on the cognitive function of the elderly existed. In 2008, an epidemiological study of 719 Japanese men found that tofu intake was associated with worse memory, but tempeh (a fermented soy product) intake was associated with better memory. This study replicated other studies.
From 1992 to 2003, sales have experienced a 15% compound annual growth rate, increasing from $300 million to $3.9 billion over 11 years, as new soyfood categories have been introduced, soyfoods have been repositioned in the market place, thanks to a better emphasis on marketing nutrition.
In 1995, the New England Journal of Medicine (Vol. 333, No. 5) published a meta-analysis financed by DuPont Protein Technologies International (PIT), which produces and markets soy through . The meta-analysis concluded that soy protein is correlated with significant decreases in serum cholesterol, LDL (bad cholesterol) and triglycerides. However, HDL(good cholesterol) did not increase by a significant amount. Soy phytoestrogens (isoflavones: genistein and daidzein) adsorbed onto the soy protein were suggested as the agent reducing serum cholesterol levels. On the basis of this research PTI filed a petition with FDA in 1998 for a health claim that soy protein may reduce cholesterol and the risk of heart disease.
The FDA granted the following health claim for soy: "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." One serving, (1 cup or 240 mL) of soy milk, for instance, contains 6 or 7 grams of soy protein. Solae resubmitted their original petition, asking for a more vague health claim, after their original was challenged and highly criticized. Solae also submitted a petition for a health claim that soy can help prevent cancer. They quickly withdrew the petition for lack of evidence and after more than 1,000 letters of protest were received. In February 18, 2008 Weston A. Price Foundation submitted a petition for removal of this health claim.
In January 2006 an American Heart Association review (in the journal "Circulation") of a decade long study of soy protein benefits casts doubt on the FDA allowed "Heart Healthy" claim for soy protein and did not recommend isoflavone supplementation. The review panel also found that soy isoflavones have not been shown to reduce post menopause "hot flashes" in women and the efficacy and safety of isoflavones to help prevent cancers of the breast, uterus or prostate is in question.
Health risks
Phytoestrogen
Soybeans contain isoflavones called genistein and daidzein, which are one source of phytoestrogens in the human diet. Because most naturally occurring estrogenic substances show weak activity, normal consumption of foods that contain these phytoestrogens should not provide sufficient amounts to elicit a physiological response in humans.
Plant lignans associated with high fiber foods such as cereal brans and beans are the principal precursor to mammalian lignans which have an ability to bind to human estrogen sites. Soybeans are a significant source of mammalian lignan precursor secoisolariciresinol containing 13–273 µg/100 g dry weight. Another phytoestrogen in the human diet with estrogen activity is coumestans, which are found in beans, split-peas, with the best sources being alfalfa, clover, and soybean sprouts. Coumestrol, an isoflavone coumarin derivative is the only coumestan in foods.
Soybeans and processed soy foods do not contain the highest "total phytoestrogen" content of foods. A study in which data were presented on an as-is (wet) basis per 100 g and per serving found that food groups from highest to lowest levels of total phytoestrogens per 100 g are nuts and oilseeds, soy products, cereals and breads, legumes, meat products, various processed foods that may contain soy, vegetables, and fruits.
Women
A 2001 literature review suggested that women with current or past breast cancer should be aware of the risks of potential tumor growth when taking soy products, based on the effect of phytoestrogens to promote breast cancer cell growth in animals.
A 2006 commentary reviewed the relationship with soy and breast cancer. They stated that soy may prevent breast cancer, but cautioned that the impact of isoflavones on breast tissue needs to be evaluated at the cellular level in women at high risk for breast cancer.
A high consumption of omega-6 polyunsaturated fatty acids, which are found in most types of vegetable oil including soybean oil, may increase the likelihood that postmenopausal women will develop breast cancer. Other analysis suggested an inverse association between total polyunsaturated fatty acids and breast cancer risk.
Men
Because of the phytoestrogen content, some studies, but not all, have suggested that there is an inverse correlation between soybean ingestion and testosterone in men. For this reason, they may protect against the development of prostate cancer. A theoretical decrease in the risk of prostate cancer should, however, be weighed against the possible side-effects of decreased testosterone, which are still unclear. The popular fear that soybeans might cause reduced libido and even feminine characteristics in men has not been indicated by any study; the popularity of the notion seems to be based on the simplistic misapprehension that estrogen and testosterone have a simple, inverse relationship in sexual hormone systems and sex-related behaviour. Their interplay is very complicated and largely still unknown.
A study published in April 2008 concluded that soy food intake has an inverse association with sperm concentration in fertility-deficient men. The same study found that soy intake does not affect sperm motility, morphology or ejaculate volume.
Infant formula
There are some studies that state that phytoestrogen in soy can lead to alterations in the proliferation and migration of intestinal cells. The effects of these alterations are unknown. However, some studies conclude there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy-based infant formula. Other reviews agree, but state that more research is needed to answer the question of what effect phytoestrogens have on infants. Soy formula has also been linked to autoimmune disorders of the thyroid gland.
Allergy
Allergy to soy is often said to be rather common, and the food is listed with other foods that commonly cause allergy, such as milk, eggs, peanuts, tree nuts, shellfish. However, a critical review of medical literature reveals surprisingly little solid information on the topic. The problem has been reported amongst younger children and the diagnosis of soy allergy is often based on symptoms reported by parents and/or results of skin tests or blood tests for allergy. Only a few reported studies have attempted to confirm allergy to soy by direct challenge with the food under controlled conditions. In these circumstances it is clear that skin/blood tests considerably overestimate the problem, as do parental reports. It is very difficult to give a reliable estimate of the true prevalence of soy allergy in the general population. To the extent that it does exist, soy allergy may cause cases of urticaria (hives) and angioedema (swelling), usually within minutes to two hours of ingestion of the food. In rare, severe cases true anaphylaxis may occur, a condition that is much more common with allergy to foods such as peanut and shellfish. The reason for the discrepancy is likely that soy proteins, the causative factor in allergy, are far less potent at triggering allergy symptoms than the proteins of peanut and shellfish. An allergy test that is positive demonstrates that the immune system has formed IgE antibodies to soy proteins. However, when soy is ingested proteins must evade digestion and be absorbed in a form capable of triggering allergy and also in sufficient quantities to reach a threshold to provoke actual symptoms. The low potency of soy proteins as allergens may help explain why allergy skin/blood tests suggest that soy allergy is common, yet few cases are confirmed when the food is eaten under observation.
Soy can also trigger symptoms via food intolerance, a situation where no immunologic (allergic) mechanism can be proven. One scenario is seen in very young infants who have vomiting and diarrhoea when fed soy-based formula. The symptoms resolve when the formula is withdrawn and recur when it is re-administered. Older infants can suffer a more severe disorder with vomiting, diarrhoea that may be bloody, anemia, weight loss and failure to thrive. The commonest cause of this unusual disorder is a sensitivity to cow's milk, but there is no doubt that soy formulas can also be the trigger. The precise mechanism is unclear and it could be immunologic, although not through the IgE-type antibodies that have the leading role in urticaria and anaphylaxis. Fortunately it is also self-limiting and will often disappear in the toddler years.
Promotion as health food
Soy consumption has been promoted by natural food companies and the soy industry's aggressive marketing campaign in various magazines, television ads and in health food markets. Research has been conducted examining the validity of the beneficial health claims with regard to the increase in consumption of soybeans which mimic hormonal activity.
A practice guideline published in the journal Circulation questions the efficacy and safety of soy isoflavones for preventing or treating cancer of the breast, endometrium, and prostate (although the same study also concludes that soy in some foods should be beneficial to cardiovascular and overall health) and does not recommend usage of isoflavone supplements in food or pills. A review of the available studies by the United States' Health and Human Services' Agency for Healthcare Research and Quality (AHRQ) found little evidence of substantial health improvements and no adverse effects, but also noted that there was no long-term safety data on estrogenic effects from soy consumption.
Brain
Estrogen helps protect and repair the brain during and after injury. The mimicry of estrogen by the phytoestrogens in soy has introduced a controversy over whether such a replacement is harmful or helpful to the brain. Several studies have found soy to be harmful for rats. Nevertheless the cited study was based on rats fed with concentrated phytoestrogens and not common soybeans. The common amounts of phytoestrogens in soy beans are not to be compared to concentrated estrogen.
One study followed over 3000 Japanese men between 1965 and 1999, and that showed a positive correlation between brain atrophy and consumption of tofu.. This study by L.R. White, et al., from the National Institute of Aging, NIH, was rejected as not credible by the Food and Drug Administration. A study on elderly Indonesian men and women found that tempeh consumption was independently related to better memory.
Carcinogen
Raw soy flour is known to cause pancreatic cancer in rats. Whether this is also true in humans is unknown because no studies comparing cases of pancreatic cancer and soy intake in humans have yet been conducted, and the doses used to induce pancreatic cancer in rats are said to be larger than humans would normally consume. Heated soy flour may not be carcinogenic in rats. Existing cancer patients are being warned to avoid foods rich in soy because they can accelerate the growth of tumours.
Soybean futures
Soybean futures are traded on the Chicago Board of Trade and have delivery dates in January (F), March (H), May (K), July (N), August (Q), September (U), November (X).
It is also traded on other commodity futures exchanges under different contract specifications:
- SAFEX: The South African Futures Exchange
- DC: Dalian Commodity Exchange
- KEX: Kansai Commodities Exchange in Japan
- TGE: Tokyo Grain Exchange in Japan
- KCX: Fukuoka Commodity Exchange in Japan that was absorbed by the KEX
See also
External links
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