Soybean

Germination

The first stage of growth is germination, a method which first becomes apparent as a seed's radicle emerges.^[14] This is the first stage of root growth and occurs within the first 48 hours under ideal growing conditions. The first photosynthetic structures, the cotyledons, develop from the hypocotyl, the first plant structure to emerge from the soil. These cotyledons both act as leaves and as a source of nutrients for the immature plant, providing the seedling nutrition for its first 7 to 10 days.^[14]

soya bean fruit

Maturation

The first true leaves develop as a pair of single blades.^[14] Subsequent to this first pair, mature nodes form compound leaves with three blades. Mature trifoliolate leaves, having three to four leaflets per leaf, are often between 6–15 cm (2.4–5.9 in) long and 2–7 cm (0.79–2.76 in) broad. Under ideal conditions, stem growth continues, producing new nodes every four days. Before flowering, roots can grow 1.9 cm (0.75 in) per day. If rhizobia are present, root nodulation begins by the time the third node appears. Nodulation typically continues for 8 weeks before the symbiotic infection process stabilizes.^[14] The final characteristics of a soybean plant are variable, with factors such as genetics, soil quality, and climate affecting its form; however, fully mature soybean plants are generally between 51–127 cm (20–50 in) in height^[15] and have rooting depths between 76–152 cm (30–60 in).^[16]

Flowering

Soybean flower buds

Flowering is triggered by day length, often beginning once days become shorter than 12.8 hours.^[14] This trait is highly variable however, with different varieties reacting differently to changing day length.^[17] Soybeans form inconspicuous, self-fertile flowers which are borne in the axil of the leaf and are white, pink or purple. Depending of the soybean variety, node growth may cease once flowering begins. Strains that continue nodal development after flowering are termed "indeterminates" and are best suited to climates with longer growing seasons.^[14] Often soybeans drop their leaves before the seeds are fully mature.

Small, purple soybean flowers

The fruit is a hairy pod that grows in clusters of three to five, each pod is 3–8 cm (1.2–3.1 in) long and usually contains two to four (rarely more) seeds 5–11 mm in diameter. Soybean seeds come in a wide variety sizes and hull colors such as black, brown, yellow, and green.^[15] Variegated and bicolored seed coats are also common.

Seed resilience

Mature soybeans

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.^[18] Patents were awarded to him in the early 1990s on techniques for protecting "biological membranes" and proteins in the dry state.

Nitrogen-fixing ability

Like many legumes, soybeans can fix atmospheric nitrogen, thanks to symbiotic bacteria from the Rhizobia group.^[19]

Nutrition

100 grams of raw soybeans supply 446 calories and are 9% water, 30% carbohydrates, 20% total fat and 36% protein (table).

Soybeans are an exceptional source of essential nutrients, providing in a 100 gram serving (raw, for reference) high contents of the Daily Value (DV) especially for protein (36% DV), dietary fiber (37%), iron (121%), manganese (120%), phosphorus (101%) and several B vitamins, including folate (94%) (table). High contents also exist for vitamin K, magnesium, zinc and potassium (table).

For human consumption, soybeans must be cooked with "wet" heat to destroy the trypsin inhibitors (serine protease inhibitors). Raw soybeans, including the immature green form, are toxic to all monogastric animals.^[21]

Protein

Further information: Complete protein, Protein quality, and Soy protein

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.

Soy is a good source of protein 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:^[22]

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.

The Protein Digestibility Corrected Amino Acid Score (PDCAAS) of 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.^[23]

Soy protein is essentially identical to the protein of other legume seeds and pulses.^[24][25] Moreover, soybeans can produce at least twice as much protein per acre than any other major vegetable or grain crop besides hemp, five to 10 times more protein per acre than land set aside for grazing animals to make milk, and up to 15 times more protein per acre than land set aside for meat production.^[26]

Graded seed

All spermatophytes, except for the grass-cereal family, contain soybean-like 7S (vicilin) or 11S (legumin), (S denotes Svedberg, sedimentation coefficients) seed storage globulin proteins. Oats and rice are anomalous in that they also contain a majority of soybean-like protein.^[27] Cocoa, for example, contains the 7S globulin, which contributes to cocoa/chocolate taste and aroma;,^[28][29][30] whereas coffee beans (coffee grounds) contain the 11S globulin responsible for coffee's aroma and flavor.^[31][32]

Vicilin and legumin proteins belong to the cupin superfamily, a large family of functionally diverse proteins that have a common origin and whose evolution can be followed from bacteria to eukaryotes including animals and higher plants.^[33]

2S albumins form a major group of homologous storage proteins in many dicot species and in some monocots but not in grasses (cereals).^[34] Soybeans contain a small but significant 2S storage protein.^[35][36][37] 2S albumin are grouped in the prolamin superfamily.^[38] Other allergenic proteins included in this 'superfamily' are the non-specific plant lipid transfer proteins, alpha amylase inhibitor, trypsin inhibitors, and prolamin storage proteins of cereals and grasses.^[27]

Peanuts, for instance, contain 20% 2S albumin but only 6% 7S globulin and 74% 11S.^[34] It is the high 2S albumin and low 7S globulin that is responsible for the relatively low lysine content of peanut protein compared to soy protein.

Comparison to other major staple foods

The following table shows the nutrient content of green soybean and other major staple foods, each in respective raw form. Raw soybeans, however, aren't edible and cannot be digested. These must be sprouted, or prepared and cooked for human consumption. In sprouted and cooked form, the relative nutritional and anti-nutritional contents of each of these grains is remarkably different from that of raw form of these grains reported in this table. The nutritional value of soybean and each cooked staple depends on the processing and the method of cooking: boiling, frying, roasting, baking, etc.

Uses

Soybeans are a globally important crop, providing oil and protein. In the United States, the bulk of the harvest is solvent-extracted with hexane, and the "toasted" defatted soymeal (50% protein) then makes possible the raising of farm animals (e.g. chicken, hog, turkey) on a large industrial scale. Soybean products are used in a large variety of processed foods.

During World War II, soybeans became important in both North America and Europe chiefly as substitutes for other protein foods and as a source of edible oil. During the war, the soybean was discovered as fertilizer by the United States Department of Agriculture.

Conditions

Cultivation is successful in climates with hot summers, with optimum growing conditions in mean temperatures of 20 to 30 °C (68 to 86 °F); temperatures of below 20 °C and over 40 °C (68 °F, 104 °F) stunt 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). For best results, though, an inoculum of the correct strain of bacteria should be mixed with the soybean (or any legume) seed before planting. Modern crop cultivars generally reach a height of around 1 m (3.3 ft), and take 80–120 days from sowing to harvesting.

Soya Fields in Argentina

Environmental issues

Environmental groups, such as Greenpeace and the WWF, have reported soybean cultivation (primarily as a feed crop for animals) and the probability of increased soybean cultivation in Brazil has destroyed huge areas of Amazon rainforest, and is encouraging further deforestation.^[45][46][47] However, note that the driving cause of this deforestation is the global demand for meat, which in turn demands huge amounts of land to grow feed crops for livestock. According to the World Bank, animal agriculture is responsible for up to 91% of the destruction of the Amazon rainforest.^[48][49][50]

Soils

Soil scientists Edson Lobato (Brazil), Andrew McClung (U.S.), and Alysson Paolinelli (Brazil) were awarded the 2006 World Food Prize for transforming the ecologically biodiverse savannah of the Cerrado region of Brazil into highly productive cropland that could grow profitable soybeans.^[51][52][53] However, even correcting for poor soils soybeans were an unlikely cash crop for the Cerrado. Soy did not fare well in the low latitudes. More than the heat and humidity, it was a lack of seasons that hampered production. In the higher more northerly latitudes, flowering coincides with the summer solstice, when the plants reach their maximum height. The first soybeans planted in the Cerrado, however, flowered early and, deprived of long summer days, remained stunted. For soy agriculture to take root in Mato Grosso it was first necessary to develop a "tropical soybean"—one that would flower later, giving the plants more time to fully mature. This was accomplished after years of crossbreeding by scientists within Embrapa, the research arm of the Brazilian Ministry of Agriculture.^[54][55]

Soybean rust

Contamination concerns

Human sewage sludge can be used as fertilizer to grow soybeans. Soybeans grown in sewage sludge likely contain elevated concentrations of metals.^[56][57]

Pests

Soybean plants are vulnerable to a wide range of bacterial diseases, fungal diseases, viral diseases and parasites. One important pest is the corn earworm moth, which is the most common and destructive pest of soybean growth in Virginia.^[58]

East Asia

The closest living relative of the soybean is Glycine soja (previously called G. ussuriensis), a legume native to central China.^[68] According to the ancient Chinese myth, in 2853 BC, the legendary Emperor Shennong of China proclaimed that five plants were sacred: soybeans, rice, wheat, barley, and millet.^[69] Cultivation of soybeans took place over long periods of time in the prehistory of modern-day Japan, Korea and Northern China, based on archaeological evidence.

The origin of soy bean cultivation remains scientifically debated. Early Chinese records mention that soybeans were a gift from the region of Yangtze River delta and Southeast China.^[70] Recent research, however, indicates that seeding of wild forms started early (before 5000 BC) in multiple locations throughout East Asia^[71] The Great Soviet Encyclopedia claims soybean cultivation originated in China about 5000 years ago.^[72] Some scholars suggest that soybean originated in China and was domesticated about 3500 BC.^[73] However, the oldest preserved soybeans resembling modern varieties in size and shape were found in archaeological sites in Korea dated about 1000 BC.^[70][74] Radiocarbon dating of soybean samples recovered through flotation during excavations at the Early Mumun period Okbang site in Korea indicated soybean was cultivated as a food crop in around 1000–900 BC.^[74] Soybeans from the Jōmon period in Japan from 3000 BC^[71] are also significantly larger than wild varieties.^[71][75] The cultivation of soybeans began in the eastern half of northern China by 2000 BC, but is almost certainly much older.^[76] Soybeans became an important crop by the Zhou Dynasty (c. 1046 – 256 BC) in China. However, the details of where, when, and under what circumstances soybean developed a close relationship with people are poorly understood. Soy bean was unknown in South China before the Han period.^[71] From about the first century AD to the Age of Discovery (15–16th centuries), soybeans were introduced into across South and Southeast Asia. This spread 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.

Many people have claimed 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,^[77] and there is evidence of tofu consumption that dates to 220.^[78]

Southeast Asia

Soybeans were mentioned as kadêlê (modern Indonesian term: kedelai)^[79] in an old Javanese manuscript, Serat Sri Tanjung, which dates around the 12th to 13th century Java.^[80] By the 13th century, the soybean had arrived and cultivated in Indonesia; it probably arrived much earlier however, carried by traders or merchants from Southern China.^[81]

The earliest known reference to it as "tempeh" appeared in 1815 in the Serat Centhini manuscript.^[82] The development of tempeh fermented soybean cake were probably took place earlier, circa 17th century in Java.

South Asia

By the 1600s, soy sauce spread from southern Japan across the region through the Dutch East India Company (VOC). The soybean probably arrived from southern China, moving southwest into northern parts of Indian Subcontinent by this period.^[83]

Iberia

In 1603, "Vocabvlario da Lingoa de Iapam", a famous Japanese-Portuguese dictionary, was compiled and published by Jesuit priests in Nagasaki. It contains short but clear definitions for about 20 words related to soyfoods - the first in any European language.

The Luso-Hispanic traders were familiar with soybeans and soybean product through their trade with Far East since at least 17th century. However, it was not until the late 19th century that the first attempt to cultivate soybeans in the Iberian peninsula was undertaken. In 1880, the soybean was first cultivated in Portugal in the Botanical Gardens at Coimbra (Crespi 1935).

In about 1910 in Spain the first attempts at Soybean cultivation were made by the Count of San Bernardo, who cultivated soybeans on his estates at Almillo (in southwest Spain) about 48 miles east-northeast of Seville.^[84]

North America

Soybeans were first introduced to North America from China in 1765, by Samuel Bowen, a former East India Company sailor who had visited China in conjunction with James Flint, the first Englishman legally permitted by the Chinese authorities to learn Chinese.^[85] The first "New World" soybean crop was grown on Skidaway Island, Georgia in 1765 by Henry Yonge from seeds given him by Samuel Bowen.^[86][87][88] Bowen grew soy near Savannah, Georgia, possibly using funds from Flint, and made soy sauce for sale to England.^[89] Although, soybean was introduced into North America in 1765, for the next 155 years, the crop was grown primarily for forage.^[90]

In 1831, the first soy product "a few dozen India Soy" [sauce] arrived in Canada. Soybeans were probably first cultivated in Canada by 1855, and definitely in 1895 at Ontario Agricultural College.^[91]

It was not until Lafayette Mendel and Thomas Burr Osborne showed that the nutritional value of soybean seeds could be increased by cooking, moisture or heat, that soy went from a farm animal feed to a human food.^[92][93]

William Morse is considered the "father" of modern soybean agriculture in America. He and Charles Piper (Dr. C. V. Piper) took what was an unknown Oriental peasant crop in 1910 and transformed it into a "golden bean" for America becoming one of America's largest farm crops and its most nutritious.^[94][95][96]

Prior to the 1920 in the USA, the soybean was mainly a forage crop, a source of oil, meal (for feed) and industrial products, with very little used as food. However, it took on an important role 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 to meet with government demands, and Henry Ford became a promoter of soybeans. He 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. It never reached the commercial market. Soybean oil was used to paint the automobiles,^[97] as well as fluid for shock absorbers.

Tofu was introduced in Japanese American internment camps during World War II, and gradually spread into the mainstream cuisine. New varieties were developed to improve the blandness of soybean oil. The Counterculture in the San Francisco region popularize soy foods. Although practically unseen in 1900, by 2000 they covered upward of 70 million acres, second only to corn, and it became America's largest cash crop.^[98]

Caribbean and West Indies

The soybean arrived in the Caribbean in the form of soy sauce made by Samuel Bowen in Savannah, Georgia, in 1767. It remains only a minor crop there, but its uses for human food are growing steadily.^[99]

Mediterranean area

The soybean was first cultivated in Italy by 1760 in the Botanical Garden of Turin. During the 1780s it was grown in at least three other botanical gardens in Italy.^[100]

In 1935 soybeans are first introduced to Greece by Anton Brillmayer, an Austrian soybean breeder.^[101] By 1939, soybeans have been cultivated in Greece.^[102]

An entire book has been published on the history of soybeans and soyfoods in Greece.^[103]

Australia

Wild soybeans were discovered in northeastern Australia in 1770 by explorers Banks and Solander. In 1804, the first soyfood product ("Fine India Soy" [sauce]) was sold in Sydney. In 1879, the first domesticated soybeans arrived in Australia, a gift of the Minister of the Interior Department, Japan.^[104]

Western Europe

The soybean was first cultivated in France by 1779 (and perhaps as early as 1740). The two key early people and organizations introducing the soybean to France were the Society of Acclimatization (starting in 1855) and Li Yu-ying (from 1910). Li started a large tofu factory, where the first commercial soyfoods in France were made.^[105]

Africa

The soybean first arrived in Africa via Egypt in 1857.^[106]

Central Europe

In 1873, Professor Friedrich J. Haberlandt first became interested in soybeans when he obtained the seeds of 19 soybean varieties at the Vienna World Exposition (Wiener Weltausstellung). He cultivated these seeds in Vienna, and soon began to distribute them throughout Central and Western Europe. In 1875, he first grew the soybeans in Vienna, then in early 1876 he sent samples of seeds to seven cooperators in central Europe, who planted and tested the seeds in the spring of 1876, with good or fairly good results in each case.^[107] Most of the farmers who received seeds from him cultivated them, then reported their results back to him. Starting in Feb. 1876, he published these results first in various journal articles, and finally in his magnum opus, Die Sojabohne (The Soybean) in 1878. In northern Europe lupin/lupine is known as the "soybean of the north"^[108]

A Hitler Youth manual from the 1930s promoted soy beans, which it called "Nazi beans" as an alternative to meat.^[109]

Central Asia

The soybean is first in cultivated Transcaucasia in Central Asia in 1876, by the Dungans. This region has never been important for soybean production.^[110]

Central America

The first reliable reference to the soybean in this region dates from Mexico in 1877.^[111]

South America

The soybean first arrived in South America in Argentina in 1882.^[112]

Andrew McClung showed in the early 1950s that with soil amendments the Cerrado region of Brazil would grow soybeans.^[113] The march of soybeans into deforested areas of the Amazon rain forest would come later.^[54]

Soybean oil

Soybean seed contains 18–19% oil.^[125] 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.

Soybean meal

Soybean meal, or soymeal, is the material remaining after solvent extraction of oil from soybean flakes, with a 50% soy protein content. The meal is 'toasted' (a misnomer because the heat treatment is with moist steam) and ground in a hammer mill. Ninety-seven percent of soybean meal production globally is used as livestock feed.^[125] Soybean meal is also used in some dog foods.^[126]

Livestock feed

One of the major uses of soybeans globally is as livestock feed, predominantly in the form of soybean meal. Spring grasses are rich in omega-3 fatty acids, whereas soy is predominantly omega-6. The soybean hulls, which mainly consist of the outer coats of the beans removed before oil extraction, can also be fed to livestock, as well as whole soybean seeds after processing.^[127][128]

Food for human consumption

Tempeh, fermented soybean cake

In addition to their use in livestock feed, soybean products are widely used for human consumption. Common soybean products include soy sauce, soy milk, tofu, soy meal, soy flour, textured vegetable protein (TVP), tempeh, soy lecithin and soybean oil. Soybeans may also be eaten with minimal processing, for example in the Japanese food edamame (枝豆, edamame), in which immature soybeans are boiled whole in their pods and served with salt.

One type of soya chunk as meal maker

In China, Japan, and Korea, soybean and soybean products are a common part of the diet. Tofu (豆腐 dòufu) is thought to have originated in China, along with soy sauce and several varieties of soybean paste used as seasonings. Japanese foods made from soya include miso (味噌), nattō (納豆), kinako (黄粉) and edamame (枝豆), as well as products made with tofu such as atsuage and aburaage. In Korean cuisine, soybean sprouts (콩나물 kongnamul) are used in a variety of dishes, and are the base ingredient in doenjang, cheonggukjang and ganjang. In Vietnam, soybeans are used to make soybean paste (tương) in the North with the most popular products are tương Bần, tương Nam Đàn, tương Cự Đà as a garnish for phở and gỏi cuốn dishes, as well as tofu (đậu hũ or đậu phụ or tàu hũ), soy sauce (nước tương), soy milk (nước đậu in the North or sữa đậu nành in the South), and đậu hũ nước đường (tofu sweet soup). In India, textured vegetable protein is often called meal maker or soya chunks and is a popular substitute for meat.

Flour

Wikimedia Commons has media related to Soybean flour.

Japanese soybean meat

Soy flour refers to soybeans ground finely enough to pass through a 100-mesh or smaller screen where special care was taken during desolventizing (not toasted) to minimize denaturation of the protein to retain a high protein dispersibility index, for uses such as food extrusion of textured vegetable protein. It is the starting material for production of soy concentrate and soy protein isolate.

Soy flour is made by roasting the soybean, removing the coat, and grinding into a flour. Soy flour is manufactured with different fat levels.^[129] Alternatively, raw soy flour omits the roasting step.

• Defatted soy flour is obtained from solvent extracted flakes, and contains less than 1% oil.^[129]
• "Natural or full-fat soy flour is made from unextracted, dehulled beans, and contains about 18% to 20% oil."^[129] Its high oil content requires the use of a specialized Alpine Fine Impact Mill to grind rather than the usual hammer mill. Full-fat soy flour has a lower protein concentration than defatted flour. Extruded Full-Fat soy flour, ground in an Alpine mill, can replace/extend EGGS in baking and cooking^[130][131] Full-fat soy flour is a component of the famous Cornell Bread recipe (think pizza)^{[132][133][134]}
• Low-fat soy flour is made by adding some oil back into defatted soy flour. Fat levels range from 4.5% to 9%.^[129]
• High-fat soy flour can also be produced by adding back soybean oil to defatted flour, usually at the level of 15%.^[135]

Soy lecithin can be added (up to 15%) to soy flour to make lecithinated soy flour. It increases dispersibility and gives it emulsifying properties.^[129]

Soy flour has 50% protein and 5% fiber. It has higher levels of protein, thiamine, riboflavin, phosphorus, calcium, and iron than wheat flour. It does not contain gluten.^[129] As a result, yeast-raised breads made with soy flour are dense in texture. Among many uses, soy flour thickens sauces, prevents staling in baked food, and reduces oil absorption during frying. Baking food with soy flour gives it tenderness, moistness, a rich color, and a fine texture.^[129]

Soy grits are similar to soy flour except the soybeans have been toasted and cracked into coarse pieces.

Kinako is a soy flour used in Japanese cuisine.

Section reference: Smith & Circle (1972, p. 442)

Soy-based infant formula

A Malaysian Soy milk carton, and a glass of the beverage

Soy-based infant formula (SBIF) is sometimes given to infants who are not being strictly breastfed; it can be useful for infants who are either allergic to pasteurized cow milk proteins or who are being fed a vegan diet. 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.^[136] 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.^{[137][138][139]} One of these studies, published in the Journal of Nutrition,^[139] concludes that there are:

... no clinical concerns with respect to nutritional adequacy, sexual development, neurobehavioral development, immune development, or thyroid disease. SBIFs provide complete nutrition that adequately supports normal infant growth and development. FDA has accepted SBIFs as safe for use as the sole source of nutrition.

Meat and dairy alternatives and extenders

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 alternatives (e.g. veggie burgers). These substitutes are readily available in most supermarkets. Soy milk does not naturally contain significant amounts of digestible calcium. Many manufacturers of soy milk sell calcium-enriched products, as well. Soy is also used in tempeh: the beans (sometimes mixed with grain) are fermented into a solid cake.

Soy products also are used as a low-cost substitute in meat and poultry products.^[140][141] Food service, retail and institutional (primarily school lunch and correctional) facilities regularly use such "extended" products. Extension may result in diminished flavor, but fat and cholesterol are reduced. Vitamin and mineral fortification can be used to make soy products nutritionally equivalent to animal protein; the protein quality is already roughly equivalent. The soy-based meat substitute textured vegetable protein has been used for more than 50 years as a way of inexpensively extending ground beef without reducing its nutritional value.^{[26][4][142][143]}

Other products

Soybeans with black hulls are used in Chinese fermented black beans, douchi, not to be confused with 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.^[146] Soybeans have also been used since 2001 as fermenting stock in the manufacture of a brand of vodka.^[147] In 1936, Ford Motor Company developed a method where soybeans and fibers were rolled together producing a soup which was then pressed into various parts for their cars, from the distributor cap to knobs on the dash board. Ford also informed in public relation releases that in 1935 over five million acres (20,000 km²) was dedicated to growing soybeans in the United States.^[148]

Cancer

According to the American Cancer Society, "Studies in humans have not shown harm from eating soy foods. Moderate consumption of soy foods appears safe for both breast cancer survivors and the general population, and may even lower breast cancer risk." There is insufficient research to indicate whether taking soy dietary supplements has any effect on health or cancer risk.^[149]

Phytochemicals

Saponins, a class of natural surfactants (soaps), are sterols that are present naturally in a wide variety of plant foods, including vegetables, legumes, and cereals such as oats.^[150] Whole soybeans contain from 0.17 to 6.16% saponins, 0.35 to 2.3% in defatted soy flour and 0.06 to 1.9% in tofu. Legumes such as soybean and chickpeas are the major source of saponins in the human diet. Sources of non-dietary saponins include alfalfa, sunflower, herbs and barbasco.

Soy contains isoflavones like genistein and daidzein,^[151] and glycitein, an O-methylated isoflavone which accounts for 5–10% of the total isoflavones in soy food products. Glycitein is a phytoestrogen with weak estrogenic activity, comparable to that of the other soy isoflavones.^[152]

Cholesterol and heart diseases

The dramatic increase in soyfood sales is largely credited to the Food and Drug Administration's (FDA) approval of soy as a cholesterol-lowering food, along with other heart and health benefits.^[22]

A 1995 review^[156] 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.^[157] Soy phytoestrogens (isoflavones: genistein and daidzein) adsorbed onto the soy protein were suggested as the agent reducing serum cholesterol levels.

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."^[22] One serving, (1 cup or 240 mL) of soy milk, for instance, contains 6 or 7 grams of soy protein. Solae resubmitted their original petition, asking for a more vague health claim, after their original was challenged and highly criticized. Solae also submitted a petition for a health claim that soy can help prevent cancer. They quickly withdrew the petition for lack of evidence and after more than 1,000 letters of protest were received. On 18 February 2008, Weston A. Price Foundation submitted a petition for removal of this health claim.^[158] 25 g/day soy protein was established as the threshold intake because most trials used at least this much protein and not because less than this amount is inefficacious. In fact, there is evidence suggesting that lower amounts are indeed efficacious.^[159]

An American Heart Association (AHA) 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-menopausal "hot flashes" and the efficacy and safety of isoflavones to help prevent cancers of the breast, uterus or prostate is in question. However, AHA concludes that "many soy products 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".^[153]

The AHA did not conduct a formal statistical analysis of the 22 studies upon which they based their estimate of the potency of soy protein. When such an analysis was conducted, Jenkins et al.^[160] found that the AHA had considerably underestimated the hypocholesterolemic effects of soy protein. Further, when the analysis was limited to the 11 studies that provided evidence that the control and soy diets were matched, soy protein was found to lower LDL by 5.2 percent. This estimate is in line with the results of other recently published meta-analyses.^{[161][162][163]} Furthermore, recent research suggests that soy protein decreases postprandial triglyceride levels, which is increasingly viewed as important for reducing coronary heart disease risk.^[164]

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,^[165] minimizing diabetes,^[166] and reducing inflammation.^[167] However, phytic acid is also criticized for reducing vital minerals absorption due to its chelating effect, especially for diets already low in minerals.^[168]

Allergy

Allergy to soy is common, and the food is listed with other foods that commonly cause allergy, such as milk, eggs, peanuts, tree nuts, shellfish. The problem has been reported among younger children, and the diagnosis of soy allergy is often based on symptoms reported by parents and 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.^[169] It is very difficult to give a reliable estimate of the true prevalence of soy allergy in the general population. To the extent that it does exist, soy allergy may cause cases of urticaria and angioedema, usually within minutes to hours of ingestion. In rare cases, true anaphylaxis may also occur. The reason for the discrepancy is likely that soy proteins, the causative factor in allergy, are far less potent at triggering allergy symptoms than the proteins of peanut and shellfish.^[170] An allergy test that is positive demonstrates that the immune system has formed IgE antibodies to soy proteins. However, this is only a factor when soy proteins reach the blood without being digested, in sufficient quantities to reach a threshold to provoke actual symptoms.

Soy can also trigger symptoms via food intolerance, a situation where no allergic mechanism can be proven. One scenario is seen in very young infants who have vomiting and diarrhoea when fed soy-based formula, which resolves when the formula is withdrawn. Older infants can suffer a more severe disorder with vomiting, diarrhoea that may be bloody, anemia, weight loss and failure to thrive. The most common cause of this unusual disorder is a sensitivity to cow's milk, but soy formulas can also be the trigger. The precise mechanism is unclear and it could be immunologic, although not through the IgE-type antibodies that have the leading role in urticaria and anaphylaxis. However, it is also self-limiting and will often disappear in the toddler years.^[171]

Phytoestrogens

Soybeans contain isoflavones called genistein and daidzein, which are one source of phytoestrogens in the human diet. Because most naturally occurring phytoestrogens act as selective estrogen receptor modulators, or SERMs, which do not necessarily act as direct agonists of estrogen receptors, normal consumption of foods that contain these phytoestrogens should not provide sufficient amounts to elicit a physiological response in humans.^[172][173]

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.^[174] 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.^[175][176]

Soybeans and processed soy foods are among the richest foods in total phytoestrogens (wet basis per 100 g), which are present primarily in the form of the isoflavones daidzein and genistein.^[177] Human breast milk-containing or cow milk formula-containing diets provide 0.005-0.01 mg of isoflavone per day, while soy-based infant formulas provide 6–47 mg of isoflavone daily. This intake is several orders of magnitude greater than those provided by other nutrients.^[178]

Breast cancer

Although considerable research has examined the potential for soy consumption to lower the risk of breast cancer in women, assessment of these studies indicates there is insufficient population evidence to make a conclusion about this relationship as of 2016.^[151]

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.^[179] A 2006 commentary reviewed the relationship with soy and breast cancer, stating that soy may decrease the risk of 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.^[180]

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.^[181] Another analysis suggests an inverse association between total polyunsaturated fatty acid intake and breast cancer risk.^[182]

A 2011 analysis of the literature said: "Our study suggests soy isoflavones intake is associated with a significant reduced risk of breast cancer incidence in Asian populations, but not in Western populations."^[183]

Prostate cancer

Because of the phytoestrogen content, some studies have suggested that soybean ingestion may influence testosterone levels in men. However, a 2010 meta-analysis of 15 placebo controlled studies showed that neither soy foods nor isoflavone supplements alter measures of bioavailable testosterone or estrogen concentrations in men.^[184] It has been hypothesized that soy foods and enterolactone may increase the development of prostate cancer although no significant associations were observed for the soy isoflavones.^[185] Furthermore, soy consumption has been shown to have no effect on the levels and quality of sperm.^[186] A 2009 meta-analysis of the research on the association between soy consumption and prostate cancer risk in men concluded that "consumption of soy foods is associated with a reduction in prostate cancer risk in men."^[187]

Brain

Because of mixed results from animal studies and epidemiological studies, a (relatively definitive but expensive) controlled study of the impacts of soy on cognitive skills was performed; it found no impact.

Though there is some evidence that estrogen can help protect and repair the brain after injury in rats,^[188] there is also evidence that phytoestrogens may be harmful for the recovery of rats in other situations^[189] that have sustained brain injury.

Similarly, epidemiological evidence of humans eating soya products is currently divided: a study of Japanese men between 1965 and 1999 demonstrated a positive correlation between brain atrophy and consumption of tofu meals.^[190]

A 2001 literature review noted that disturbing data on soy's effect on the cognitive function of the elderly existed.^[191] In 2008, an epidemiological study of 719 Indonesian elderly individuals found that tofu intake was associated with worse memory, but tempeh (a fermented soy product) intake was associated with better memory.^[192]

The cover article in the Center for Science in the Public Interest's September 2014 newsletter reported that a controlled study at USC prompted by suggestive epidemiological evidence found no impact on cognitive skills of years of soy vs milk protein diet enrichment.^[193]

Carcinogenicity

Though raw soy flour is known to be correlated with pancreatic cancer in rats^[194] the cooked flour has not been found carcinogenic.^[195][196] Whether soy might promote pancreatic cancer in humans is unknown because studies have not yet attempted to single out soy intake and the incidence of pancreatic cancer in humans, and the amount of soy fed to the rats is proportionately far larger than what humans would normally consume. However, the soy isoflavone genistein has been suggested as a chemopreventive agent against pancreatic cancer, by interfering with the chemical pathways that promote the creation and growth of tumors.^[197]

The Cancer Council of New South Wales, Australia has released a statement saying scientific research suggests that overall the moderate consumption of soy products does not appear to present a risk to women with breast cancer, and there is equivocal evidence that consuming large amounts of soy products may have a protective effect against developing breast and prostate cancer. However, the Council does not recommend taking soy dietary supplements as there is no evidence they are either effective or safe at preventing or treating cancers.

Thyroid function

One review noted that soy based foods may inhibit absorption of thyroid hormone medications required for treatment of hypothyroidism.^[198] A 2015 scientific review by the European Food Safety Authority concluded that intake of isoflavones from supplements did not affect thyroid hormone levels in postmenopausal women.^[199]

Gout

Soybeans and soy products contain significant amounts of purines, a class of organic compounds. For people who suffer from gout, eating foods containing moderate or high levels of purines may make the condition worse. The U.S. National Institutes of Health (NIH) recommends that gout sufferers limit consumption of soy products (although also suggesting that soy may have health benefits by reducing the risk for heart disease).^[200] However, other researchers have found little or no association between consumption of purine-rich vegetables (including beans) and gout.^[201][202]