|Glycine max |
Fat-free (defatted) soybean meal is a primary, low-cost, source of protein for animal feeds and most prepackaged meals; soy vegetable oil is another valuable product of processing the soybean crop. For example, soybean products such as textured vegetable protein (TVP) are important ingredients in many meat and dairy analogues.
Traditional nonfermented food uses of soybeans include soy milk, and from the latter tofu and tofu skin. Fermented foods include soy sauce, fermented bean paste, natto, and tempeh, among others. The oil is used in many industrial applications. The main producers of soy are the United States (32%), Brazil (28%), Argentina (21%), China (7%) and India (4%). The beans contain significant amounts of phytic acid, alpha-Linolenic acid, and the isoflavones genistein and daidzein.
Soybeans can produce at least twice as much protein per acre as any other major vegetable or grain crop, 5 to 10 times more protein per acre than land set aside for grazing animals to make milk, and up to 15 times more protein per acre than land set aside for meat production.
NameThe plant is sometimes referred to as greater bean (大豆 - Chinese dàdòu and Japanese daizu). In Vietnam, the plant is called đậu tương or đậu nành. Both immature soybean and its dish are called edamame in Japan, but in English, edamame refers only to a specific dish.
The English word "soy" is derived from the Japanese pronunciation of shōyu (醤油, しょうゆ), the Japanese word for soya sauce; "soya" comes from the Dutch adaptation of the same word.
ClassificationGlycine was originally introduced by Carl Linnaeus (1737) in his first edition of Genera Plantarum. The word glycine is derived from the Greek - glykys (sweet) and 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 Species Plantarum, by 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.
The genus Glycine Willd. is divided into two subgenera, Glycine and Soja. The subgenus Soja (Moench) F.J. Herm. includes the cultivated soybean, Glycine max (L.) Merr., and the wild soybean, Glycine soja Sieb. & Zucc. Both species are annual. Glycine soja is the wild ancestor of Glycine max and grows wild in China, Japan, Korea, Taiwan and Russia. The subgenus Glycine consists of at least 16 wild perennial species: for example, Glycine canescens F.J. Herm. and G. tomentella Hayata, both found in Australia and Papua New Guinea.
Like some other crops of long domestication, the relationship of the modern soybean 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.
Description and physical characteristicsSoy varies in growth and habit. The height of the plant varies from below 20 cm (7.9 in) up to 2 metres (6.6 ft).
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 (2.4–5.9 in) long and 2–7 cm (0.79–2.8 in) broad. The leaves fall before the seeds are mature. The inconspicuous, self-fertile flowers are borne in the axil of the leaf and are white, pink or purple.
fruit is a hairy pod that grows in clusters of 3–5, each pod is 3–8 cm long (1–3 in) 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
|Nutritional value per 100 g (3.5 oz)|
|Energy||1,866 kJ (446 kcal)|
|Dietary fiber||9.3 g|
|Aspartic acid||5.112 g|
|Glutamic acid||7.874 g|
|Vitamin A equiv.||1 μg (0%)|
|Vitamin B6||0.377 mg (29%)|
|Vitamin B12||0 μg (0%)|
|Vitamin C||6.0 mg (10%)|
|Vitamin K||47 μg (45%)|
|Calcium||277 mg (28%)|
|Iron||15.70 mg (126%)|
|Magnesium||280 mg (76%)|
|Phosphorus||704 mg (101%)|
|Potassium||1797 mg (38%)|
|Sodium||2 mg (0%)|
|Zinc||4.89 mg (49%)|
|Percentages are relative to US recommendations for adults. |
Source: USDA Nutrient database
Most soy protein is a relatively heat-stable storage protein. This heat stability enables soy food products requiring high temperature cooking, such as tofu, soy milk and textured vegetable protein (soy flour) to be made.
The principal soluble carbohydrates 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, and methane.
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.
NutritionFor human consumption, soybeans must be cooked with "wet" heat in order to destroy the trypsin inhibitors (serine protease inhibitors). Raw soybeans, including the immature green form, are toxic to humans, swine, chickens, in fact, all monogastric animals.
Soybeans are considered by many agencies 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 vegetarians and vegans or for people who want to reduce the amount of meat they eat. According to the US Food and Drug Administration:
Soy protein products can be good substitutes for animal products because, unlike some other beans, soy offers a 'complete' protein profile. ... 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 many dietary health claims, 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, eggs, and casein 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 seeds. Moreover, soybeans can produce at least twice as much protein per acre than any other major vegetable or grain crop, 5 to 10 times more protein per acre than land set aside for grazing animals to make milk, and up to 15 times more protein per acre than land set aside for meat production.
Consumption of soy may also reduce the risk of colon cancer, possibly due to the presence of sphingolipids.
|Top Soybean Producers |
|(million metric tons)|
UN Food & Agriculture Organisation
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 United States Department of Agriculture. In the 1960-1 Dillion round of the General Agreement on Tariffs and Trade (GATT), the United States secured tariff-free access for its soybeans to the European market. In the 1960s the United States exported over 90% of the world's soybeans. In 2005, top soybeans exporters are Brazil (39% of world soybean exports), United States (37%) and Argentina ( 16%), while top importers are China (41% of world soybean imports), European Union (22%), Japan (6%) and Mexico (6%).
Cultivation is successful in climates with hot summers, with optimum growing conditions in mean temperatures of 20 to 30 °C (68 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 soybean (or any legume) seed before planting. Modern crop cultivars generally reach a height of around 1 m (3.3 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 soybean cultivation and the probability of increased soybean cultivation in Brazil has destroyed huge areas of Amazon rainforest and is encouraging further deforestation.
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.
Soybean plants are vulnerable to a wide range of bacterial diseases, fungal diseases, viral diseases and parasites.
HistorySoybeans were a crucial crop in eastern Asia long before written records. 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 18th century 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.
AsiaThe wild ancestor of the soybean is Glycine soja (previously called G. 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 myth, in 2853 BC the legendary Emperor Shennong of China proclaimed that five plants were sacred: soybeans, rice, wheat, barley, and millet. However, soy in particular was revered for its root structure as a means of crop rotation. Cultivation of soybeans was long confined chiefly to China, but gradually spread to other countries.[not in citation given]
The oldest preserved soybeans were found in archaeological sites in Korea dated about 1000 BCE, though it is uncertain if they were wild, or cultivated strains - though the size of cultivated beans, the main difference between the two is a genetic alteration that determines whether the wild pods burst to scatter seeds and neither feature could be determined from the remains. Wild-size soybeans have been found in the Yellow River basin of China. 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 1st century AD to the Age of Discovery (15-16th century), soybeans were introduced into several countries such as India, Japan, Indonesia, the Philippines, Vietnam, Thailand, Cambodia, Malaysia, Burma, Taiwan and Nepal. 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 StatesSoybeans were introduced to America in 1765 by Samuel Bowen, a sailor who had visited China. He grew soy near Savanna, Georgia and even made soy sauce for sale to England.
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, soybean oil was used to paint the automobiles as well as fluid for shock absorbers. 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 phenol formaldehyde plastics. A prototype vehicle, colloquially titled "The Soybean Car", was built in 1941 out of such 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. It was usable in the making of suits, felt hats, and overcoats. Though pilot production of Azlon reached 5000 pounds per day in 1940, it never reached the commercial market; Dupont's nylon was the winner in the quest to produce artificial silk.
Ford himself wore a suit made entirely from soybeans, and he was even said to have had dinner parties with nothing but soybean-based foods on the menu.
South AmericaThe soybean first arrived in South America in Brazil in 1882.
AfricaThe soybean first arrived in Africa in Egypt in 1857.
Australia, New Zealand, and OceaniaWild soybeans were discovered in northeastern Australia in 1770 by explorers Banks and Solander. In 1804 the first soyfood product ("Fine India Soy" [sauce]) was sold in Sydney. In 1879 the first soybeans arrived in Australia, a gift of the Minister of the Interior Department, Japan.
CanadaIn 1831 the first soy product ("A few dozen India Soy" [sauce]) arrived in Canada. Soybeans were probably first cultivated in Canada by 1855, and definitely in 1895 at Ontario Agricultural College. A comprehensive history of soy in Canada (1,060 p., 2,336 references) is available online.
Caribbean / West IndiesThe soybean arrived in the Caribbean in the form of soy sauce made by Samuel Bown in Savannah, Georgia, in 1767. It remains only a minor crop there but its uses for human food are growing steadily. A comprehensive history of soybeans and soyfoods in this region is available free online 
Central AsiaThe soybean is first in cultivated Transcaucasia in Central Asia in 1876, by the Dungans. This region has never been important for soybean production. A comprehensive history of soybeans and soyfoods in this region is available online.
Mexico and Central AmericaThe first reliable reference to the soybean in this region dates from Mexico in 1877. A comprehensive history of soybeans and soyfoods in this region is available online.
Southeast AsiaBy the 13th century the soybean had arrived in Indonesia; it probably arrived much earlier, carried by traders or merchants from southern China.
South Asia / Indian SubcontinentBy the 1600s, soy sauce was being disseminated from southern Japan throughout this region by the Dutch East India Co. (VOC). The soybean probably arrived from southern China, moving southward into northern India.
Genetic modificationbiotech food" crops that have been genetically modified, and genetically modified soybeans are being used in an increasing number of products. In 1995 Monsanto Company introduced Roundup Ready (RR) soybeans that have been genetically modified to be resistant to Monsanto's 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 2010, the figure was 93%. 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.
A 2006 United States Department of Agriculture report found that the adoption of genetically engineered (GE) soy, corn and cotton reduced the amount of pesticides used overall, but did result in a slightly greater amount of herbicides used for soy specifically. The use of GE soy was also associated with greater conservation tillage, indirectly leading to better soil conservation, as well as increased income from off-farming sources due to the greater ease with which the crops can be managed. Most farmers adopted the GE crops to improve yields, save time and reduce the amount of money spent on pesticides. The use of GE soy also permits the use of a herbicide that is less toxic to humans. Though the overall estimated benefits of the adoption of GE soybeans in the United States was $310 million, the majority of this benefit was experienced by the companies selling the seeds (40%), followed by biotechnology firms (28%) and farmers (20%).
In 2010, a team of American scientists announced they had decoded the genome of the soybean - the first legume to be sequenced.
UsesSoybeans 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 soy milk 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 there is a tendency for the pods to shatter upon 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 second most valuable agricultural export in the United States behind corn. 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 (枝豆, edamame ). In English, these soybeans are generally known as "edamame" or "green vegetable soybeans."
In China, Japan, and Korea the bean and products made from the bean are a popular part of the diet. The Chinese invented tofu (豆腐 dòufu), and also made use of several varieties of soybean paste as seasonings. Japanese foods made from soya include miso (味噌), nattō (納豆), kinako (黄粉) and edamame (枝豆). In Korean cuisine, soybean sprouts, called kongnamul (콩나물), are also used in a variety of dishes, and are also the base ingredient in doenjang, cheonggukjang and ganjang. In Vietnam, soya bean are used to make soybean paste- tương in the North with the most popular products are tương Bần, tương Nam Đàn, tương Cự Đà as a garnish of phở dish and gỏi cuốn dish), tofu (đậu hũ or đậu phụ or tàu hũ), soya sauce (nước tương, literally: soya water), soya milk (nước đậu in the North or sữa đậu nành in the South), đậu hũ nước đường (tofu sweet soup).
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 Company support the industry trade associations United Soybean Board and Soyfoods Association of North America. These trade associations have increased the consumption of soy products dramatically in recent years.
OilSoybean seed contains about 19% oil. To extract soybean oil from seed, 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 meal is used mainly as animal feed.
MealSoybean meal is the material remaining after solvent extraction of oil from soybean flakes, with a 50% soy protein content. The meal is 'toasted' (a misnomer because the heat treatment is with moist steam) and ground in a hammer mill. Soybean meal is an essential element of the American production method of growing farm animals such as poultry and swine on an industrial scale that began in the 1930s; and more recently the aquaculture of catfish. Ninety-eight percent of the U.S. soybean crop is used for livestock feed. Soybean meal is also used in lower end dog foods.
FlourSoy flour refers to defatted soybeans ground finely enough to pass through a 100-mesh or smaller screen where special care was taken during desolventizing (not toasted) in order to minimize denaturation of the protein to retain a high Protein Dispersibility Index (PDI), for uses such as extruder cooking of textured vegetable protein. 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 formulaSoy-based infant formula (SBIF) is used for infants who are allergic to pasteurized cow milk proteins. It is sold in powdered, ready-to-feed, and concentrated liquid forms.
Some reviews have expressed the opinion that more research is needed to determine what effect the phytoestrogens in soybeans may have on infants. Diverse studies have concluded 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 in the Journal of Nutrition, concludes that there are:
...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 and extendersdairy 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. Soy milk does not naturally contain significant amounts of digestible calcium. Many manufacturers of soy milk sell calcium-enriched products as well. Soy is also used in tempeh: the beans (sometimes mixed with grain) are fermented into a solid cake.
Soy products also are used as a low cost substitute in meat and poultry products. Food service, retail and institutional (primarily school lunch and correctional) facilities regularly use such "extended" products. Extension may result in 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. The soy-based meat substitute textured vegetable protein has been used for more than 50 years as a way of inexpensively extending ground beef without reducing its nutritional value.
Other productsSoybeans 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.
Cattle feedCattle are often fed soy. Spring grasses are rich in Omega-3 fatty acids whereas soy is predominantly Omega-6.
Omega-3 fatty acidsOmega-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 acid (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 (18:3n−3, aLNA) can do this. Soybean oil is one of the few common vegetable oils that contain 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: 100 g of soybean oil contains 7 g of omega-3 fatty acids to 51 g of omega-6: a ratio of 1:7. Flaxseed, in comparison, has an omega-3:omega-6 ratio of 3:1.
IsoflavonesSoybeans also contain the isoflavones genistein and daidzein, types of phytoestrogen, that are considered by some dietitians 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), and blocks formation of new blood vessels (antiangiogenic effect). Some studies show that genistein acts as inhibitor of substances that regulate cell division and cell survival (growth factors).
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.
Cholesterol reductionThe 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 Indonesian elderly 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.
In 1995, the New England Journal of Medicine (Vol. 333, No. 5) published-Title- "Meta-analysis of the effects of soy protein intake on serum lipids", financed by DuPont Protein Technologies International (PTI), which produces and markets soy through The Solae Company. 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. On February 18, 2008 Weston A. Price Foundation submitted a petition for removal of this health claim.
An American Heart Association review of a decade long study of soy protein benefits casts doubt on the FDA allowed "Heart Healthy" claim for soy protein and does 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.
Phytic acidSoybeans contain a high level of phytic acid, which has many effects including acting as an antioxidant and a chelating agent. The beneficial claims for phytic acid include reducing cancer, minimizing diabetes, and reducing inflammation. However, phytic acid is also criticized for reducing vital minerals due to its chelating effect, especially for diets already low in minerals.
AllergyAllergy to soy is common, and the food is listed with other foods that commonly cause allergy, such as milk, eggs, peanuts, tree nuts, shellfish. The problem has been reported among 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. 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 and angioedema, usually within minutes to hours of ingestion. In rare cases, true anaphylaxis may also occur. 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, this is only a factor when soy proteins reach the blood without being digested, in sufficient quantities to reach a threshold to provoke actual symptoms.
Soy can also trigger symptoms via food intolerance, a situation where no allergic mechanism can be proven. One scenario is seen in very young infants who have vomiting and diarrhoea when fed soy-based formula, which resolves when the formula is withdrawn. Older infants can suffer a more severe disorder with vomiting, diarrhoea that may be bloody, anemia, weight loss and failure to thrive. The most common cause of this unusual disorder is a sensitivity to cow's milk, but 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.
PhytoestrogenSoybeans 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 are among the richest foods in total phytoestrogens (wet basis per 100g), which are present primarily in the form of the isoflavones daidzein and genistein.
WomenA 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. Another analysis suggests an inverse association between total polyunsaturated fatty acids and breast cancer risk. A 2011 analysis of the literature concluded that:- "Our study suggests soy isoflavones intake is associated with a significant reduced risk of breast cancer incidence in Asian populations, but not in Western populations."
MenBecause of the phytoestrogen content, some studies have suggested that soybean ingestion may influence testosterone levels in men. However, a 2010 meta analysis of 15 placebo controlled studies showed that neither soy foods nor isoflavone supplements alter measures of bioavailable testosterone concentrations in men  It has been hypothesized that soy foods and enterolactone may increase the development of prostate cancer although no significant associations were observed for the soy isoflavones. Furthermore, soy consumption has been shown to have no effect on the levels and quality of sperm A 2009 meta-analysis of the research on the association between soy consumption and prostate cancer risk in men concluded that,"consumption of soy foods is associated with a reduction in prostate cancer risk in men."
BrainThere is evidence that estrogen can help protect and repair the brain after injury, and it has been suggested that the phytoestrogens in soy may have a similar effect though this is controversial and there is also evidence that phytoestrogens may be harmful for the recovery of rats that have sustained brain injury. A study of Japanese men between 1965 and 1999 demonstrated a positive correlation between brain atrophy and consumption of tofu. A study on elderly Indonesian men and women found that tempeh consumption was independently related to better memory.
CarcinogenicityThough raw soy flour is known to cause pancreatic cancer in rats the cooked flour has not been found carcinogenic. Whether soy might promote pancreatic cancer in humans is unknown because studies have not yet attempted to single out soy intake and the incidence of pancreatic cancer in humans, and the amount of soy fed to the rats is proportionately far larger than what humans would normally consume. However, the soy isoflavone genistein has been suggested as a chemopreventive agent against pancreatic cancer, by interfering with the chemical pathways that promote the creation and growth of tumors.
The Cancer Council of New South Wales, Australia has released a statement saying scientific research suggests that overall the moderate consumption of soy products does not appear to present a risk to women with breast cancer, and there is equivocal evidence that consuming large amounts of soy products may have a protective effect against developing breast and prostate cancer. However, the Council does not recommend taking soy dietary supplements as there is no evidence they are either effective or safe at preventing or treating cancers.
Soybean futuresSoybean 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: