Everything about The Soybean totally explained
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's 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
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.
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 won't
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. 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're 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
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 didn't 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.
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.
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; it also saves fossil fuels and sequesters
CO2, a greenhouse effect gas. 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. However, the RR gene has been bred into so many different soybean cultivars that the genetic modification itself hasn't resulted in any decline of genetic diversity, as demonstrated by a study on genetic diversity
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's 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.
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've 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 . 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).
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.
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
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, but didn't 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. One of these studies, published at the Journal of Nutrition,. 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 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
Protein, Vitamins, and Minerals
Soybeans are generally considered to be a source of
complete protein, without any need for
Protein combining. 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 can't 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.
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.
Role of soyfoods in disease prevention
Omega-3 fatty acids
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's 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 doesn't 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
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 and endocrine disruptive. Soy's content of isoflavones are as much as 3 mg/g dry weight.
Isoflavones are
polyphenol compounds, produced primarily by beans and other legumes, including
peanuts and
chickpeas. Isoflavones are closely related to the antioxidant
flavonoids found in other plants, vegetables and flowers. Isoflavones such as genistein and daidzein are found in only some plant families, because most plants don't 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.
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."
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) didn't 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." 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.
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 isn't 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
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 shouldn't provide sufficient amounts to elicit a physiological response in humans.
Plant
lignans associated with high fiber foods such as cereal brans and beans are the principal precursor to mammalian lignans which have an ability to bind to human estrogen sites. Soybeans are a significant source of mammalian lignan precursor
secoisolariciresinol containing 13–273 µg/100 g dry weight. Another phytoestrogen in the human diet with estrogen activity is
coumestans, which are found in beans, split-peas, with the best sources being alfalfa, clover, and soybean sprouts.
Coumestrol, an isoflavone
coumarin derivative is the only coumestan in foods.
Soybeans and processed soy foods don't 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.
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.
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.
Men
Because of the phytoestrogen content, some studies, but not all, have suggested that there's an inverse correlation between soybean ingestion and
testosterone in men. For this reason, they may protect against the development of prostate cancer. 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 hasn't 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.
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. 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. Other reviews agree, but state that more research is needed to answer the question of what effect phytoestrogens have on infants. Soy formula has also been linked to
autoimmune disorders of the
thyroid gland.
Allergens
About 9% 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. 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.
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 doesn't recommend usage of isoflavone supplements in food or pills. 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.
Brain
Estrogen helps protect and repair the brain during and after injury. 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.Nevertheless the cited study was based on rats fed with
concentrated phytoestrogens and not common soy beans and it's 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.
Carcinogen
Raw
soy flour is known to cause
pancreatic cancer in rats. 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.
Further Information
Get more info on 'Soybean'.
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