Soybean

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

Soybean, green raw

Nutritional value per 100 g (3.5 oz)
Energy	125.52 kJ (30.00 kcal)
Carbohydrates	5.94 g
Sugars	4.13 g
Dietary fiber	1.8 g
Fat	0.18 g
Saturated	0.046 g
Monounsaturated	0.022 g
Polyunsaturated	0.058 g
Protein	3.04 g
Vitamins and minerals Vitamins Quantity %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 Minerals Quantity %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 constituents	Quantity
Water	90.4 g
†Percentages estimated using US recommendations for adults, except for potassium, which is estimated based on expert recommendation from the National Academies.

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 stiffly erect up to 2 meters (6.5 feet) in height. The pods, stems, and leaves are covered with fine brown or gray pubescence. The leaves are trifoliate (sometimes with 5 leaflets), 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 small, 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.

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.

Beans are classed as pulses whereas soybeans are classed as oilseeds. The word "soy" is derived from the Chinese word 醬油 for soy sauce/soya sauce.

Physical characteristics

Soybeans occur in various sizes, and in several hull or seed coat colors, including black, brown, blue, yellow, 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.

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 twenty years ago. 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.

Leopold's research on soybeans led to techniques that allowed insulin to be dried and processed into an inhalable insulin, named Exubera by Pfizer.

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. 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. 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.

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 States	83.9 (39.15%)
2. Brazil	52.7 (24.59%)
3. Australia	44.7 (20.86%)
4. Argentina	38.3 (17.87%)
5. China	17.4 (8.12%)
6. India	6.6 (3.08%)
7. Paraguay	3.5 (1.63%)
8. Canada	3 (1.4%)
9. Bolivia	1.7 (0.79%)
World total	214.3
Source: UN Food and Agriculture Organization

Soybeans are native to southeast Asia, but 45 percent of the world's soybean area, and 55 percent of production, is in the United States. The U.S. produced 75 million metric tons of soybeans in 2000, of which more than one-third was exported. Other leading producers are Brazil, 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. American soil scientist Dr. Andrew McClung, who first showed that the infertile Cerrado region of Brazil could grow soybeans, was awarded the 2006 World Food Prize on October 19, 2006.

The first research on soybeans in the United States was conducted by George Washington Carver at Tuskegee, Alabama, but he decided it was too exotic a crop for the poor black farmers of the South so he turned his attention to peanuts. Peanuts, soybeans, or other legume plants that would replenish the soil with nitrogen and minerals were planted for two years and then cotton on the third year. A two year rotation system alternating maize instead is also a possibility.

Production history

Soyabean output in 2005

Soybean domestication first occurred in China. Ancient Chinese documents state that soybean agriculture began during the Zhou Dynasty in 664 BC and was introduced to the Zhou heartland from the Manchuria Plain . Archaeologists recovered soybean from a site in Jilin Province and dated charcoal associated with the legume to cal. 900–520 BC.

The earliest known soybeans were unearthed from archaeological sites in Korea . For example, AMS radiocarbon dating on soybean recovered through flotation during excavations at the Early Mumun Period Okbang site in Korea clearly indicates that soybean was cultivated as a food crop in cal. 1000–900 BC. . Although the Korean peninsula is usually considered to be an area of secondary agricultural origins, similar research on Azuki bean indicates that, in addition to Northeast China, the Korean Peninsula was an early center of importance related to the domestication and cultivation of legumes . The best current evidence on the Japanese Archipelago suggests that soybean cultivation occurred in the early Yayoi period.

Soybean diseases

Main article: List of soybean diseases

Genetic modification

Soybeans are one of the "biotech food" crops that are being 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, by means of a gene gun, into its genome that allows the transgenic plant to survive being sprayed by this non-selective herbicide, glyphosate. Glyphosate, the active ingredient in Roundup, kills conventional soybeans. The bacterial gene is EPSP (5-enolpyruvyl shikimic acid-3-phosphate) synthase. Soybean also has a version of this gene, but the soybean version is sensitive to glyphosate, while the CP4 version is not.

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' or conservation tillage. No-till agriculture has many advantages, greatly reducing soil erosion and creating better wildlife habitat; it also saves fossil fuels and sequesters CO2, a greenhouse effect gas. It must be said, however, that the production and use of an artificial herbicide such as Roundup does consume significant quantities of fossil fuels and does not improve wildlife habitat since it is designed specifically to kill most plants.

In 1997, about 8% of all soybeans cultivated for the commercial market in the United States were genetically modified. In 2006, the figure was 89%. As with other "Roundup Ready" crops, concern is expressed over damage to biodiversity. However, the RR gene has been bred into so many different soybean cultivars that the genetic modification itself has not resulted in any decline of genetic diversity.

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. Japanese foods made from soya include: miso (味噌), natto (納豆), tofu (豆腐) 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, 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 is 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 metric 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.

Soybean oil has also been found effective as an insect repellent in some studies. 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 revolution, 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 human milk proteins and cow milk proteins. The formulas are sold in powdered, ready-to-feed, or concentrated liquid forms.

It has been recommended internationally by pediatric associations that soy formulas not be used as the primary or sole source of nutrition for infants due to the high risk of several deficiencies, including calcium and zinc. Some studies have also indicated that soy may act similarly to the hormone estrogen in developing infants. This has caused some concern that soy formula may cause undesirable side effects, such as reproductive problems. However, no studies to date have shown any negative effects on infants resulting from the estrogen-like compounds in soy formula.

Substitute for existing products

Many traditional dairy products have been made without dairy using processed soybeans, and products such as soy milk, soy yogurt and soy cream cheese are readily available in most supermarkets. These products are derived from extensive processing to produce a texture and appearance similar to dairy-based ones. 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 also used in industrial products including oils, soap, cosmetics, resins, plastics, inks, crayons, solvents, clothing, and biodiesel. Soybeans are also used as fermenting stock to make a brand of vodka.

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 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

Protein, Vitamins, and Minerals

Main article: soy protein

Soybeans are generally considered to be a source of complete protein, although this is contested by some sources. 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.

However, the phrase complete protein can be misleading since proteins vary in their protein values. Whey protein has a BV of 100, egg white protein is 83, and soybean protein isolate is 74. 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.

Toasted soybeans

Consumption of soy may also reduce the risk of colon cancer, possibly due to the presence of sphingolipids.

The role of soyfoods in disease prevention

Omega-3 fatty acids

Omega-3 fatty acids, for example, 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 which may inhbit conversion of aLNA to the biologically active forms EPA and DHA, which is at best limited in humans anyway.

Isoflavones

Main article: Isoflavone

Soybeans also contain isoflavones, a type of phytoestrogen, that are considered by some nutritionists and physicians to be useful in the prevention of cancer and by others to be carcinogenic and endocrine disruptive. Soy's high levels of isoflavone phytoestrogens, being up to 3mg/g dry weight, are the subject of heated debate and controversy.{Pfact}} They are also blamed for some thyroid and reproductive health problems.

Isoflavones are polyphenol compounds, produced primarily by beans and other legumes, including peanuts and chickpeas. Although isoflavones are closely related to the antioxidant flavonoids found in plants, vegetables and flowers, isoflavones such as genistein and daidzein are found in very few plant families. This is because of the restricted distribution of the enzyme, chalcone isomerase which converts a flavone precursor into an isoflavone, to tropical legumes.

Claims of cholesterol reduction

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

From 1992 to 2003, soyfoods 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." 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 250mg/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." 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 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. 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." The original paper is in the journal Circulation: January 17, 2006.

Soy controversy

Phytoestrogen

Main article: Phytoestrogens

Soybeans contain isoflavones called genistein and daidzein. Soybean isoflavonoids are one of a number of primary sources of phytoestrogens in the human diet that mimic estrogen. Since most naturally occurring estrogenic substances show only weak activity, it is doubtful that normal consumption of foods that contain these phytoestrogens would provide sufficient amounts to elicit a physiological response in humans. Genistein is only 10 raised to the -5 (1/100,000)as active as the synthetic estrogen, diethylstilbestrol; and daidzein, the other isoflavone in soybeans, is in turn only 1/4 as active as genistein.

Plant lignans associated with high fiber foods such as cereal brans and beans are the principal precursor to mammalian lignans which have an ability to bind to human estrogen sites. Soybeans are a significant source of mammalian lignan precursor secoisolariciresinol containing 13–273 µg/100 g dry weight. Another phytoestrogen in the human diet with estrogen activity is coumestans, which are found in beans, split-peas, with the best sources being alfalfa, clover, and soybean sprouts. Coumestrol, an isoflavone coumarin derivative is the only coumestan in foods.

Soybeans and processed soy foods do not contain the highest "total phytoestrogen" content of foods. A study in which data were presented on an as is (wet) basis per 100 g and per serving found that food groups with decreasing 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. Soy products contain the highest amounts of isoflavone. The richest sources of specific phytoestrogens, including coumestrol, were also identified. This database will improve phytoestrogen intake estimation in future studies.

Allergens

Further information: Soy allergy

With the increased use of soybean in western diet comes also a danger of food allergies. Up to 8% of children in the USA are allergic to soybean proteins. The major soy allergen has been identified by scientists at USDA. Both transgenic and conventional soybean varieties without the allergenic protein have been prepared, and hopefully will soon reach the market. This will be particularly important for preparation of baby formulas, since dual allergy to both milk and soy proteins is not unheard of. Soya allergy, typically, will manifest itself approximately a day after consumption of the beans. Common symptoms are urticaria, rash, itching, and redness of the skin.

Soy and the brain

There is considerable evidence that estrogen aids in protecting the brain and helping it recover after injury. This mimicry of estrogen by phytoestrogens introduces a controversy over whether such a replacement is harmful or helpful to the brain. The study most often cited indicating soy to be harmful was a study that followed over 3000 Japanese men between 1965 and 1999, and that showed a positive correlation between brain atrophy and consumption of tofu. This is a single study that by itself does not show conclusively that soy causes brain atrophy. This study was rejected as not credible by the Food and Drug Administration when it issued its 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."[1]

There are articles that imply that soy benefits the brain and reduces the possibility of Alzheimer's Disease. One three-year animal study found that the phytoestrogens of soy reduced protein alterations in the brain that are indicative of Alzheimer's. Further studies must be done to determine the positive and/or negative effects of soy on the brain.

Health food stores and soy

Soy consumption has been popularized by natural food companies and the soy industry's 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.

External links

Advocacy and general information

• Guardian - There's no risk to humans from soya
• Evaluation of Anti-Soy Data and Anti-Soy Advocates
• Cornell University Food and Brand Lab
• Soya information

Critical

• "Newest Research on Why You Should Avoid Soy" by Sally Fallon and Mary Enig
• Argentina Soya-fication Brings serious environmental, social and economic problems
• Concerns Regarding Soybeans
• Why Soy Can Damage Your Health
• Guardian - Should we worry about soya in our food?
• Soy's Thyroid Dangers
• Soy Allergens
• Soy Allergy Information Page Asthma and Allergy Foundation of America
• Health Canada: Soy - One of the nine most common food allergens
• Soya 'Link' To Male Infertility
• Soy Online Service
• Soy Alert!
• "AlterNet: Health & Wellness: The Dark Side of Soy". Retrieved 2007-07-09.