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"Soy" redirects here. For other uses, see Soy (disambiguation).

Soybean
Scientific classification
Kingdom:
Plantae
Phylum:
Magnoliophyta
Class:
Magnoliopsida
Order:
Fabales
Family:
Fabaceae
Subfamily:
Faboideae
Genus:
Glycine
Species:
G. max
Binomial name
Glycine L. max

The soybean (U.S.) or soya bean (UK) (Glycine max) is a species of legume native to East Asia. It is an annual plant that may vary in growth, habit, and height. It may grow prostrate, not growing higher than 20 cm (7.8 inches), or even up to 2 meters (6.5 feet) in height. The pods, stems, and leaves are covered with fine brown or gray hairs. The leaves are trifoliolate, having 3 to4 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, with each pod 3–8 cm (1–3 inches) long and usually containing 2–4 (rarely more) seeds 5–11 mm in diameter.

Overview

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 (a cultigen) with a very large number of cultivars. However, it is known that the progenitor of the modern soybean was a vine-like plant that grew prone on the ground.

The genus Glycine Willd. 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, Europe, and Papua New Guinea[1]

Beans are classed as pulses whereas soybeans are classed as oilseeds. It is a versatile bean, having a diverse range of uses.

The English word soy is derived from the Japanese pronunciation of 醤油 (しょうゆ, shōyu), the Japanese word for soy sauce; soya comes from the Dutch adaptation of the same word.[2][3]

Physical characteristics

Soybeans occur in various sizes, and in four 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 oil.

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.[4] 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

The oil and protein content together 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 soybean 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, nitrogen, methane, etc.

Since soluble soy carbohydrates are found mainly in the whey and are broken down during fermentation, soy concentrate, soy protein isolates, tofu, soy sauce, and sprouted soybeans 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.

Cultivation

Varieties of soybeans are used for many purposes.

Soybeans are an important global crop, providing oil and protein. The bulk of the crop is solvent-extracted for vegetable oil and then defatted soy meal 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.

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.[citation needed] Soy was first introduced to Europe in the early 1700s and 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 utilized as a food prior to the 1920s. Soy was introduced in Africa from China in the late 19th Century and is now widespread across the continent.

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.

Top Soybean producers
in 2005
Numbers in million tonnes
1.  United States83.9 (39.15%)
2.  Brazil52.7 (24.59%)
3.  Australia44.7 (20.86%)
4.  Argentina38.3 (17.87%)
5.  China17.4 (8.12%)
6.  India6.6 (3.08%)
7.  Paraguay3.5 (1.63%)
8.  Canada3 (1.4%)
9.  Bolivia1.6 (0.75%)
World total214.3
Source: UN Food and Agriculture Organization

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, Australia, Argentina, 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.[5] 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.[6]

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.

Production history

Soybean output in 2005

According to the ancient Chinese, in 2853 BC the legendary Emperor Shennong of China named five sacred plants – soybeans, rice, wheat, barley, and millet.[7] 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.[8] The soybean has been used in China for 5,000 years as a food and a component of drugs. Cultivation of the soybean, long confined chiefly to China, gradually spread to other countries.[9]

According to other sources, the earliest preserved soybeans were unearthed from archaeological sites in Korea.[10][11] AMS radiocarbon dating on soybean 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.[12] The best current evidence on the Japanese Archipelago suggests that soybean cultivation occurred in the early Yayoi period.

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, Nepal and India. The spread of the soybean was due to the establishment of sea and land trade routes. The earliest Japanese textual reference to the soybean is in the classic Kojiki (Records of Ancient Matters) which was completed in 712 AD.

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. In the United States they are now a leading crop, and Brazil, Argentina, and Paraguay also are significant soybean-exporting nations.

Many people have claimed that soybeans in Asia, prior to modern times, were only used after a fermentation process, which alters the high increase in phytoestrogens found in the raw plant. However, this appears to be incorrect: Terms similar to "soy milk" have been in use since 82 AD [1], and there is evidence of tofu consumption that dates to 220.[2]

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 . Some alternative names are: ground nut, American potato bean, wild bean, Indian potato, ground bean, hopniss, and sea vines. The seeds are also edible. It saved the Massachusetts Bay Pilgrims from starvation.[13] 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.

Soybean diseases

Main article: List of soybean diseases

Genetic modification

Soybeans are one of the "biotech food" crops that have been genetically modified, and GM soybeans are being used in an increasing number of products. In 1995 Monsanto introduced Roundup Ready (RR) soybeans that have had a copy of a gene from the bacterium, Agrobacterium sp. strain CP4, inserted into its genome by means of a gene gun, that allows the transgenic plant to survive being sprayed by this non-selective herbicide, Roundup. Glyphosate, the active ingredient in Roundup, kills conventional soybeans. The bacterial gene is EPSP (5-enolpyruvyl shikimic acid-3-phosphate) synthase. Soybeans also have a version of this gene, but the soybean version is sensitive to glyphosate, while the CP4 version is not.[14]

RR soybeans allow a farmer to spray widely the herbicide Roundup and so to reduce tillage or even to sow the seed directly into an unplowed field, known as no-till farming or conservation tillage. No-till agriculture has many advantages, greatly reducing soil erosion and creating better wildlife habitat;[15] it also saves fossil fuels and sequesters CO2, a greenhouse effect gas.[16] It should be noted that RR soybeans simplify the process, but are not a requirement for no-till agriculture. Roundup may be sprayed on the field (and weeds) before the non-RR soybeans have emerged from the soil.

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.[17] 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 study on genetic diversity[18]

The ubiquitous 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 extensive 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.[19]

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 edamame (枝豆). Soybeans prepared this way are a popular local snack in Hawaii, and are becoming increasingly popular in the continental United States. 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 (豆腐), and also made use of several varieties of soybean paste as seasonings. Japanese foods made from soya include: miso (味噌), natto (納豆), and edamame (枝豆). In Korean cuisine, soybean sprouts, called kongnamul (hangul: 콩나물) 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).

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 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, 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 trans fat configuration, whereas in nature the configuration is cis. This external picture 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.[20]

Soybean oil has also been found effective as an insect repellent in some studies.[21][22] The commercial product Bite Blocker contains soybean oil as one active ingredient.

Meal

Main article: Soybean 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 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,[23][24] 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.[25][26][27] One of these studies, published at the Journal of Nutrition,[27] 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.

Nut butter

Soybeans have been made into a spread called soynut butter, similar to peanut butter but with soybeans instead. Soy nut butter is made from fresh roasted whole soybeans. It is remarkably similar to peanut butter in taste and texture but has significantly less total and saturated fat than peanut butter and is cholesterol free. It is also suitable for those allergic to nuts or to butter.

Substitute for existing products

Open package of cream cheese with chives, a soy milk based cream cheese alternative

Soybeans are the primary ingredient in many processed foods, including dairy product substitutes (e.g., margarine, soy ice cream, soy milk, soy yogurt, soy cheese and soy cream cheese), as well as Crisco, soybean oil, tofu, veggie burgers, soy crisps, among others. Soybeans are processed to produce a texture and appearance similar to other foods (e.g., butter, ice cream, milk, yogurt, cheese, lard, olive oil, ground beef, potato chips, etc.) and are readily available in most supermarkets. Soy milk does not contain significant amounts of calcium, since the high calcium content of soybeans is bound to the insoluble constituents and remains in the pulp. Many manufacturers of soy milk now sell calcium-enriched products as well.

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 [28]. Soybeans are also used as fermenting stock to make a brand of vodka.[citation needed]

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.

Today, very high quality textile fibers are made commercially from "okara" (soy pulp), a by-product of tofu production.

Nutrition

Soybean, green raw
Nutritional value per 100 g (3.5 oz)
Energy125.52 kJ (30.00 kcal)
5.94 g
Sugars4.13 g
Dietary fiber1.8 g
0.18 g
Saturated0.046 g
Monounsaturated0.022 g
Polyunsaturated0.058 g
3.04 g
Vitamins and minerals
VitaminsQuantity
%DV†
Vitamin A equiv.
0%
1 μg
Vitamin B6
5%
0.088 mg
Vitamin B12
0%
0 μg
Vitamin C
15%
13.2 mg
Vitamin K
28%
33 μg
MineralsQuantity
%DV†
Calcium
1%
13 mg
Copper
18%
0.164 mg
Iron
5%
0.91 mg
Magnesium
5%
21 mg
Phosphorus
4%
54 mg
Potassium
5%
149 mg
Sodium
0%
6 mg
Zinc
4%
0.41 mg
Other constituentsQuantity
Water90.4 g
†Percentages estimated using US recommendations for adults,[29] except for potassium, which is estimated based on expert recommendation from the National Academies.[30]

Protein, Vitamins, and Minerals

Main article: soy protein

Soybeans are generally considered to be a source of complete protein, without any need for Protein combining.[31] although this is contested by some sources.[32][33] 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.

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.[34]

Soy protein is similar to that of other legume seeds, but 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.[35]

Role of soyfoods in disease prevention

Omega-3 fatty acids

Toasted soybeans

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, 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

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[citation needed] and endocrine disruptive[citation needed]. 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 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.

Claims of cholesterol reduction

The dramatic increase in soyfood sales is largely credited to the Food and Drug Administration's (FDA) approval of health claims for soy in which studies are conflicting as to their cholesterol lowering ability.[36]

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 report from the University of Kentucky entitled, "Meta-Analysis of the Effects of Soy Protein Intake on Serum Lipids." It was financed by the PTI division of DuPont,"The Solae Co."[37] St. Louis, Missouri, a soy producer and marketer. This meta-analysis concluded that soy protein is correlated with significant decreases in serum cholesterol, Low Density Lipoprotein LDL (bad cholesterol) and triglyceride concentrations. However, High Density Lipoprotein 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, in 1998, filed a petition with FDA for a health claim that soy protein may reduce cholesterol and the risk of heart disease. It should be noted that only subjects with serum cholesterol of 250 mg/dl and higher showed any improvement in the study.

The FDA granted this 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."[38] 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.[39]

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. This review of the literature compared soy protein and its component isoflavones with casein (isolated milk protein), wheat protein, and mixed animal proteins.[40] 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. Thus, soy isoflavone supplements in food or pills is not recommended. Among the conclusions the authors state, "In contrast, soy products such as tofu, soy butter, soy nuts, or some soy burgers should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat. Using these and other soy foods to replace foods high in animal protein that contain saturated fat and cholesterol may confer benefits to cardiovascular health."[41] The original paper is in the journal Circulation: January 17, 2006.[42]

Soy controversy

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.[43] 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.[44][45]

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.[46]

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 on breast cancer cell growth in animals.[47]

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.[48]

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.[49] For this reason, they may protect against the development of prostate cancer.[50] 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 gender-based behavior. Their interplay is very complicated and largely still unknown. [51]

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.[52] 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.[53] Other reviews agree, but state that more research is needed to answer the question of what effect phytoestrogens have on infants.[54][55] Soy formula has also been linked to autoimmune disorders of the thyroid gland.[56]

Allergens

Main article: Soy allergy

About 9% of children in the USA are allergic to soybean proteins.[citation needed] The major soy allergen has been identified by scientists at USDA.[citation needed] Both transgenic and conventional soybean varieties without the allergenic protein have been prepared.[citation needed] Soy allergy, typically, will manifest itself approximately a day after consumption of the beans. Common symptoms are urticaria, rash, itching, and redness of the skin.[57][58]

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.[59] 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 soy consumption.[60]

Brain

Estrogen helps protect and repair the brain during and after injury.[61] 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.[62]Nevertheless the cited study was based on rats fed with concentrated phytoestrogens and not common soy beans and it is already well known that concentrated estrogens cause negative effects in males. 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.[63]

Carcinogen

Raw soy flour is known to cause pancreatic cancer in rats.[64] 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.[65][66]

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