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Soybean
The soybean (U.S.) or soya bean (UK) (commonly misspelled "Soyabean") (Glycine max) is a species oflegume native to East Asia. The plant is classed as anoilseed rather than a pulse. It is an annual plant that has been used in China for 5,000 years to primarily add nitrogen into the soil as part of crop rotation. The plant is sometimes referred to as greater bean (China - 大豆 dàdòu) or edamame (Japan), though the latter is more commonly used in English when referring to a specific dish. In Vietnam, the plant is called đậu tương or đậu nành.
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.
Fat-free(defatted) soybean meal is a primary, relatively low-cost, source of protein for animal feeds or rations; soy vegetable oil is another valuable product of processing the soybean crop. Soybean products such as TVP (textured vegetable protein), for example, are important ingredients in many meat and dairy analogues; and very safe in combination with ground beef,etc.[1]
Traditional nonfermented food uses of soybeans includesoymilk, and from the latter Tofu and tofu skin or yuba. Fermented foods include shoyu or soy sauce, miso, natto,tempeh, Ketjap[2] 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%).[3][4] The beans contain significant amounts of phytic acid, alpha-Linolenic acid, and theisoflavones genistein and daidzein.
Varieties of soybeans are used for many purposes.
The genus name Glycine 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 asApios americana. The cultivated soybean first appeared inSpecies Plantarum, by Linnaeus, under the name Phaseolusmax 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, Glycineand 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 sojais the wild ancestor of Glycine max and grows wild in China, Japan, Korea, Taiwan and Russia.[5] The subgenus Glycineconsists 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.[6][7]
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.
[edit]Description and physical characteristics
Soy varies in growth, habit, and height. It may grow 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 inconspicuous, self-fertile flowers are borne in the axil of the leaf and are white, pink or purple.
Small, purple soybean flowers.
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.[8]Patents were awarded to him in the early 1990s on techniques for protecting "biological membranes" and proteins in the dry state. Compare to tardigrades.
[edit]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.
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, andpectin. The majority of soybean carbohydrates can be classed as belonging to dietary fiber.
[edit]Nutrition
Further information: Soy protein
For human consumption, soybeans must be cooked with "wet" heat in order to destroy the trypsin inhibitors (serine protease inhibitors). It is not advisable to eat raw soybeans.
Soybeans are considered by many agencies to be a source of complete protein.[9] 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.[9]
However, as with many dietary health claims, there are opposing viewpoints on the health benefits of soybeans.[10][11]
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.[12]
Soy protein is essentially identical to that of other legume seeds.[13] Moreover, it has the highest yield per square meter of growing area, and is the least expensive source of dietary protein.[citation needed]
Consumption of soy may also reduce the risk of colon cancer, possibly due to the presence of sphingolipids.[14]
Soybean output in 2005
Soybeans are an important global crop, providing oil and protein. In the United States, the bulk of the crop has its oil solvent-extracted with hexane, then the "toasted" defatted soymeal (50% protein) makes possible the raising of farm animals (eg. chicken, hog, turkey) on an industrial scale never before seen in human history. A very 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 Americaand 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.[15][16] 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%).[17]
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 soybean (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 soybean cultivation and the probability of increased soybean cultivation in Brazil has destroyed huge areas of Amazon rainforestand is encouraging further deforestation.[18]
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 Prizeon October 19, 2006.[19]
Soybean plants are vulnerable to a wide range of bacterial diseases, fungal diseases, viral diseases and parasites.
Further information: List of soybean diseases
Soybeans were a crucial crop in eastern Asia long before written records.[citation needed] 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.[citation needed] Soy was first introduced toEurope 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.
The wild ancestor of the soybean is Glycine soja (previously called G. ussuriensis), a legume native to central China[20]. 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.[21] However, Soy in particular was revered for its root structure as a means of crop rotation and not as a food source. Cultivation of soybeans was long confined chiefly to China, but gradually spread to other countries.[22]
The earliest preserved soybeans were found in archaeological sites in Korea.[23][24] Radiocarbon datingof 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.[25]
From about the first 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, 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,[26] and there is evidence of tofu consumption that dates to 220.[27]
[edit]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, soybean oil was used to paint the automobiles[28] 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.[29]
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.[citation needed]
[edit]Genetic modification
Different varieties of soybeans being grown together
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 Company introducedRoundup Ready (RR) soybeans that have been genetically modified to be resistant to the herbicideRoundup 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.[30]
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.[31] 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.[32]
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 theEuropean 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.[33]
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 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?). Because of the proclaimed health benefits of soy, edamame has been featured as an ideal snack alternative in fitness and healthy living magazines. 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 (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) andedamame (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 aretương Bần, tương Nam Đàn, tương Cự Đà as a garnish of phở dish and gỏi cuốn dish), tofu (đậu hũ orđậu phụ or tàu hũ), soya sauce (nước tương, literally: soya water), soya milk (nước đậu in the North orsữa đậu nành in the South), đậu hũ nước đường (tofu sweet soup).
In India, black soybean is popular in the Himalayan regions of the country (esp. Uttarakhand), where it is consumed in various ways similar to pulses.
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).
Soybeans grow throughout Asia and North and South America.
Soybean fields in the United States
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.
Main article: Soybean oil
Soyabean 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 husks are used mainly as animal feed.
Main article: Soybean meal
Soybean meal is the material remaining after solvent extraction of oil from soybean flakes, with a 50% soy protein content. The meal is 'toasted' (a misnomerbecause 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 theaquaculture of catfish. Ninety-eight percent of the U.S. soybean crop is used for livestock feed.[20] Soybean meal is also used in lower end dog foods.
Soy 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%.
Reference: Soybeans: Chemistry and Technology. page 442. A.K. Smith and S.J. Circle. The AVI Publishing Company,1972.
[edit]Infant formula
Soy-based infant formula (SBIF) is used for infants who are allergic to 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.[34] 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.[35][36][37] One of these studies, published in the Journal of Nutrition,[37] 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.
[edit]Meat and dairy substitutes
Open package of a soy-based cream cheese alternative with chives
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 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 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 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.
[edit]Other products
Soybeans are the bean used in Chinese fermented black beans, douchi, not the sometimes confusedblack 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.[38] Soybeans have also been used since 2001 as fermenting stock in the manufacture of a brand of vodka.[39]
[edit]Cattle feed
Cattle are often fed soy. Spring grasses are rich in Omega-3 fatty acids whereas soy is predominantly Omega-6. "Cows fed plants like alfalfa and flaxseed, substances that, unlike corn or soy, mimic the spring grasses that the animal evolved long ago to eat."[40]
[edit]Omega-3 fatty acids
Roasted soybeans
Omega-3 fatty acids, for example, alpha-linolenic acidC18-3, 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) anddocosahexaenoic 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 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.
[edit]Isoflavones
Main article: Isoflavone
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[41] and endocrine disruptive.[42][43] Soy's content of isoflavones are as much as 3 mg/g dry weight.[citation needed] Isoflavones are polyphenol compounds, produced primarily by beans and other legumes, including peanuts and chickpeas. Isoflavones are closely related to the antioxidant flavonoidsfound 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),[44] and blocks formation of new blood vessels (antiangiogenic effect).[45] 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.[46]
[edit]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.[47] 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.[48] 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.[49] 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 (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) adsorbedonto 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."[50] 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.[51]
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.[41]
[edit]Phytic acid
Main article: Phytic acid
Soybeans 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,[52] minimizing diabetes,[53] and reducing inflammation.[54] However, phytic acid is also criticized for reducing vital minerals due to its chelating effect, especially for diets already low in minerals.[55]
[edit]Phytoestrogen
Main article: Phytoestrogens
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.[citation needed]
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.[56]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 isoflavonecoumarin derivative is the only coumestan in foods.[57][58]
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.[59]
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.[60]
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.[61]
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.[62] Another analysis suggests an inverse association between total polyunsaturated fatty acids and breast cancer risk.[63]
Because of the phytoestrogen content, some studies have suggested that there is an inverse correlation between soybean ingestion and testosterone in men.[64] For this reason, they may protect against the development of prostate cancer.[65] 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 behavior. Their interplay is very complicated and still largely unknown.[66]
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.[67]
[edit]Allergy
Main article: Soy 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. 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.[68] 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.[69]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 most common 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.[70]
Estrogen helps protect and repair the brain during and after injury.[71] 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.[72] 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.[73] A study on elderly Indonesian men and women found that tempeh consumption was independently related to better memory.[49]
[edit]Carcinogen
Raw soy flour is known to cause pancreatic cancer in rats.[74] However, studies suggest heated soy flour is not carcinogenic in fat rats.[75][76] 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. The doses of soy used to induce pancreatic cancer in rats are said to be larger than humans would normally consume. In the meantime, several epidemiologic studies have found a protective effect against pancreatic cancer in high consumers of soy and other foods typical of the traditional Japanese and modern Seventh Day Adventist diet.[77]
Existing cancer patients have been advised by the Cancer Council of New South Wales, Australia to avoid high consumption of soy foods and supplements because of conflicting evidence these may accelerate the growth of hormone-dependent tumours. "While they [soy foods] may have a protective effect, there is also some evidence that phyto-oestrogens may stimulate the growth of existing hormone-dependent cancers," according to a 2007 statement by the council.[78]
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).[79]
It is also traded on other commodity futures exchanges under different contract specifications:
§ SAFEX: The South African Futures Exchange[80]
§ DC: Dalian Commodity Exchange[81]
§ KEX: Kansai Commodities Exchange in Japan[82]
§ TGE: Tokyo Grain Exchange in Japan[83]
§ KCX: Fukuoka Commodity Exchange in Japan that was absorbed by the KEX
Soy beans also come from Mack and Bewick in the city of Detroit.
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