The
soybean (U.S.) or
soya bean
(UK) (commonly misspelled "Soyabean") (
Glycine max) is a
species of
legume native to
East Asia. The plant is classed as a plant rather
than a
pulse. It is an annual plant
that has been used in China for 5,000 years to primarily add
nitrogen into the soil as part of crop rotation. The plant is
sometimes referred to as
greater bean (China) or
edamame (Japan), though the
latter is more commonly used in English when referring to a
specific dish.
In Vietnam
, the plant
is called đậu tương or đậu
nành.
The English word "soy" is derived from the Japanese pronunciation
of 醤油 (しょうゆ,
shōyu), the Japanese word for Soya
sauce; soya comes from the Dutch adaptation of the same word.
Fat-free(defatted) soybean meal is a primary, relatively low-cost,
source of protein for animal feeds or rations; soy
vegetable oil is another valuable product of
processing the soybean crop. Soybean products such as TVP (
textured vegetable protein), for
example, are important ingredients in many meat and dairy
analogues. Soybeans are also used to make
soy
sauce, and the oil is used in many industrial applications. The
main producers of soy are the United States, Brazil, Argentina,
China and India. The beans contain significant amounts of
phytic acid,
alpha-Linolenic acid, and the
isoflavones genistein
and
daidzein.
Classification
Varieties of soybeans are used for
many purposes.
The genus name
Glycine was
originally introduced by
Carl Linnaeus
(1737) in his first edition of
Genera Plantarum. The word
glycine is derived from the Greek -
glykys (sweet) and
likely refers to the sweetness of the
pear-shaped (
apios in Greek) edible tubers
produced by the native North American twining or climbing
herbaceous
legume,
Glycine apios,
now known as
Apios
americana. The cultivated soybean first appeared in
Species Plantarum, by Linnaeus,
under the name
Phaseolus max L.
The combination
Glycine max (L.) Merr., as proposed by
Merrill in 1917, has become the valid name for this useful
plant.
The genus
Glycine Willd. is
divided into two subgenera,
Glycine and
Soja. The
subgenus
Soja (Moench) F.J. Herm. includes the cultivated
soybean,
Glycine max (L.) Merr., and the wild soybean,
Glycine soja Sieb. & Zucc.
Both species are
annual.
Glycine
soja is the wild ancestor of
Glycine max and grows
wild in China, Japan, Korea, Taiwan and Russia.The subgenus
Glycine consists of at least 16 wild
perennial species: for example,
Glycine
canescens F.J. Herm. and
G. tomentella Hayata, both
found in Australia and Papua New Guinea.
Like some other crops of long domestication, the relationship of
the modern soybean to wild-growing species can no longer be traced
with any degree of certainty. It is a
cultural
variety with a very large number of cultivars.
Description and physical characteristics
Soy varies in growth, habit, and height. It may grow not higher
than 20 cm (7.8 inches), or grow up to 2 meters
(6.5 feet) high.
The pods, stems, and leaves are covered with fine brown or gray
hairs. The
leaves are trifoliolate, having 3 to
4 leaflets per leaf, and the leaflets are 6–15 cm
(2–6 inches) long and 2–7 cm (1–3 inches) broad. The
leaves fall before the seeds are mature. The inconspicuous,
self-fertile flowers are borne in the axil of the leaf and are
white, pink or purple.
Small, purple soybean flowers.
The
fruit is a hairy
pod
that grows in clusters of 3–5, each pod is 3–8 cm
long(1–3 inches) and usually contains 2–4 (rarely more)
seeds 5–11 mm in diameter.
Soybeans occur in various sizes, and in many
hull or seed coat colors, including black, brown, blue,
yellow, green and mottled. The hull of the mature bean is hard,
water resistant, and protects the
cotyledon and
hypocotyl
(or "germ") from damage. If the seed coat is cracked, the seed will
not
germinate. The scar, visible on the
seed coat, is called the hilum (colors include black, brown, buff,
gray and yellow) and at one end of the hilum is the micropyle, or
small opening in the seed coat which can allow the absorption of
water for sprouting.
Remarkably, seeds such as soybeans containing very high levels of
protein can undergo
desiccation yet survive and revive after water
absorption. A.
Carl Leopold, son of Aldo Leopold, began studying this capability at
the Boyce
Thompson Institute for Plant Research at Cornell
University
in the mid 1980s. He found soybeans and corn
to have a range of soluble
carbohydrates protecting the seed's cell
viability. 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
Together, oil and protein content account for about 60% of dry
soybeans by weight; protein at 40% and oil at 20%. The remainder
consists of 35% carbohydrate and about 5%
ash. Soybean cultivars comprise
approximately 8% seed coat or hull, 90%
cotyledons and 2%
hypocotyl axis or germ.
Most
soy protein is a relatively
heat-stable storage protein. This heat stability enables soy food
products requiring high temperature cooking, such as
tofu,
soy milk and
textured vegetable protein (soy
flour) to be made.
The principal soluble
carbohydrates of
mature soybeans are the disaccharide
sucrose
(range 2.5–8.2%), the trisaccharide
raffinose (0.1–1.0%) composed of one sucrose
molecule connected to one molecule of
galactose, and the tetrasaccharide
stachyose (1.4 to 4.1%) composed of one sucrose
connected to two molecules of galactose. While the
oligosaccharides raffinose and stachyose
protect the viability of the soy bean seed from desiccation (see
above section on physical characteristics) they are not digestible
sugars and therefore contribute to
flatulence and abdominal discomfort in humans and
other
monogastric animals; compare to
the disaccharide
trehalose. Undigested
oligosaccharides are broken down in the intestine by native
microbes producing gases such as
carbon
dioxide,
hydrogen, and
methane.
Since soluble soy carbohydrates are found in the whey and are
broken down during fermentation, soy concentrate, soy protein
isolates, tofu, soy sauce, and sprouted soy beans are without
flatus activity. On the other hand, there may be some beneficial
effects to ingesting oligosaccharides such as raffinose and
stachyose, namely, encouraging indigenous
bifidobacteria in the colon against
putrefactive bacteria.
The insoluble carbohydrates in soybeans consist of the complex
polysaccharides
cellulose,
hemicellulose, and
pectin. The majority of soybean carbohydrates can be
classed as belonging to
dietary
fiber.
Nutrition
For human consumption, soybeans must be cooked with "wet" heat in
order to destroy the
trypsin
inhibitors (
serine
protease inhibitors). It is not advisable to eat raw
soybeans.
Soybeans are considered by many agencies to be a source of
complete protein. A complete protein is one
that contains significant amounts of all the
essential amino acids that must be
provided to the
human body because of the
body's inability to
synthesize them.
For this reason, soy is a good source of protein, amongst many
others, for
vegetarians and
vegans or for people who cannot afford meat.
According to the
US Food and Drug
Administration:
Soy protein products can be good substitutes for animal
products because, unlike some other beans, soy offers a 'complete'
protein profile.
...
Soy protein products can replace animal-based
foods—which also have complete proteins but tend to contain more
fat, especially saturated fat—without requiring major adjustments
elsewhere in the diet.
However, as with many dietary health claims, there are opposing
viewpoints on the health benefits of soybeans.
The gold standard for measuring protein quality, since 1990, is the
Protein
Digestibility Corrected Amino Acid Score (PDCAAS) and by this
criterion
soy protein is the nutritional
equivalent of meat, eggs, and
casein for
human growth and health. Soybean protein
isolate has a
biological value of
74, whole soybeans 96, soybean milk 91, and eggs 97.
Soy protein is essentially identical to
that of other legume seeds.Moreover, it 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.
Cultivation
Soybean output in 2005
Soybeans are an important global crop, providing oil and protein.
In the United States, the bulk of the crop is solvent-extracted
with hexane for vegetable oil and then the "toasted" defatted
soymeal (50% protein) makes possible raising of farm animals (eg.
chicken, hog, turkey), on an industrial scale never before seen in
human history and harking back to the 1930s American promise of a
"Chicken in every pot." A very small proportion of the crop is
consumed directly by humans. Soybean products do appear in a large
variety of processed foods.
During
World War II, soybeans became
important in both
North America and
Europe chiefly as substitutes for other
protein foods and as a source of edible oil.
It was during World War II that the soybean was discovered as
fertilizer by the United States
Department of Agriculture
. In the 1960-1 Dillion round of the
General Agreement on
Tariffs and Trade (GATT), the United States secured tariff-free
access for its soybeans in the European market. In the 1960s the
United States exported over 90% of the worlds soybeans. The soybean
is now a leading crop in the United States.
Brazil
, Argentina
, and Paraguay
also are
significant soybean-exporting nations.
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 Soy bean (or any legume) seed
before planting. Modern crop
cultivars
generally reach a height of around 1 m (3 ft), and take
80–120 days from sowing to harvesting.
Soybeans are native to east Asia but only 45 percent of soybean
production is located there. The other 55 percent of production is
in the Americas. U.S.A. produced 75 million tons of soybeans in
2000, of which more than one-third was exported.
Other leading
producers are Brazil, Argentina, Paraguay, China
, and
India
.
Environmental groups, such as
Greenpeace
and the
WWF, have
reported that both soybean cultivation and the probability of
increased soybean cultivation in Brazil, has destroyed huge areas
of
Amazon rainforest and is
encouraging further
deforestation.
One of the largest consumers of soya fed cow and chickens is
McDonald's resturants. Although "McDonalds say that the
preservation of tropical rainforest is a top priority" the reality
is that they are in partnership with Cargill, who source directly
from the Amazon rainforest. When repeatedly questioned on the
segregation of Amazon from non-Amazon soya, McDonald's has been
unwilling or unable to provide evidence that it is segregating
between Amazon and non-Amazon soya, or that it is requiring its
feed suppliers do so. This is despite McDonald's public claims that
its feed is 'traceable to source'
American
soil scientist Dr. Andrew McClung, who first showed that the
ecologically biodiverse savannah of the Cerrado
region of
Brazil could grow profitable soybeans, was awarded the 2006
World Food Prize on October 19,
2006.
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.
Soybean plants are vulnerable to a wide range of bacterial
diseases, fungal diseases, viral diseases and parasites.
History
Soybeans were a crucial crop in eastern
Asia
long before written records.
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 what is now the
United
States
in 1765, where it was first grown for hay.
Benjamin Franklin wrote a letter
in 1770 mentioning sending soybeans home from England. Soybeans did
not become an important crop outside of Asia until about 1910. In
America, soy was considered an industrial product only and not used
as a food prior to the 1920s. Soy was introduced to Africa from
China in the late 19th Century and is now widespread across the
continent.
Asia
The wild
ancestor of the soybean is Glycine
soja (previously called G. ussuriensis), a legume
native to central China. The
soybean has been used in China for 5,000 years as a food and a
component of drugs. According to the ancient Chinese, in 2853 BC
the legendary
Emperor Shennong of China
proclaimed that five plants were sacred: soybeans, rice, wheat,
barley, and
millet. However, Soy in
particular was revered for its root structure as a means of crop
rotation and not as a food source. Cultivation of soybeans was long
confined chiefly to China, but gradually spread to other
countries.
The
earliest preserved soybeans were found in archaeological sites in Korea.
Radiocarbon dating of soybean
samples recovered through
flotation during
excavations at the Early
Mumun period Okbang
site in Korea indicates that soybean was cultivated as a food crop
in ca. 1000–900 BC.
From
about the first century AD to the Age
of Discovery (15-16th century), soybeans were introduced into
several countries such as India, Japan, Indonesia
, the Philippines
, Vietnam, Thailand
, Malaysia
, Burma
, Taiwan
and Nepal
. This
spread was due to the establishment of sea and land trade routes.
The best current evidence on the Japanese Archipelago suggests that
soybean cultivation occurred in the early
Yayoi period. The earliest Japanese textual
reference to the soybean is in the classic
Kojiki (Records of Ancient Matters) which was
completed in 712 AD.
Many people have claimed that soybeans in Asia were historically
only used after a fermentation process, which lowers the high
phytoestrogens content found in the
raw plant. However, terms similar to "
soy
milk" have been in use since 82 AD, and there is evidence of
tofu consumption that dates to 220.
United States
Soy took
on a very important role in the United States after World War
I. During the
Great
Depression, the drought stricken (
Dust
Bowl) regions of the United States were able to use soy to
regenerate their soil because of its nitrogen-fixing properties.
Farms were increasing production in order to meet with government
demands, and
Henry Ford was a great
leader of the soybean industry.
In 1932-33 the Ford Motor Company spent approximately $1,250,000 on
soybean research. By 1935 every Ford car had soy involved in its
manufacture. For example, soybean oil was used to
paint the automobiles as well as fluid for shock
absorbers. Ford's involvement with the soybean opened many doors
for agriculture and industry to be linked more strongly than it
ever had before.
Henry Ford promoted the soybean, helping to develop uses for it
both in food and in industrial products, even demonstrating auto
body panels made of soy-based plastics. Ford's interest led to two
bushels of soybeans being used in each Ford car as well as products
like the first commercial
soy milk, ice
cream and all-vegetable non-dairy whipped topping. The Ford
development of so-called soy-based plastics was based on the
addition of soybean flour and wood flour to
phenol formaldehyde
plastics.
In 1931, Ford hired chemists
Robert Boyer and Frank Calvert to
produce artificial silk. They succeeded in making a textile fiber
of spun soy protein fibers, hardened or tanned in a
formaldehyde bath, which was given the name
Azlon by the Federal Trade Commission. It was
usable in the making of suits, felt hats, and overcoats. Though
pilot production of Azlon reached 5000 pounds per day in 1940, it
never reached the commercial market; Dupont's
nylon was the winner in the quest to produce
artificial silk.
Ford himself wore a suit made entirely from soybeans, and he was
even said to have had dinner parties with nothing but soybean-based
foods on the menu.
Genetic modification
Different varieties of soybeans being
grown together
Soybeans are one of the "
biotech food"
crops that have been
genetically modified, and
genetically modified soybeans are being used in an increasing
number of products. In 1995
Monsanto
Company introduced
Roundup Ready
(RR) soybeans that have been genetically modified to be resistant
to the herbicide
Roundup through
substitution of the
Agrobacterium
sp. (strain CP4)
gene EPSP (5-enolpyruvyl
shikimic acid-3-phosphate) synthase. The substituted version is not
sensitive to
glyphosate.
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, as demonstrated by a 2003 study
on genetic diversity.
The widespread use of such types of GM soybeans in the Americas has
caused problems with exports to some regions. GM crops require
extensive certification before they can be legally imported into
the
European Union, where there is
considerable supplier and consumer reluctance to use GM products
for consumer or animal use. Difficulties with
coexistence and subsequent traces of cross-contamination of
non-GM stocks have caused shipments to be rejected and have put a
premium on non-GM soy.
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
soy milk producers prefer the higher
protein cultivars bred from vegetable soybeans originally brought
to the United States in the late 1930s. The "garden" cultivars are
generally not suitable for mechanical combine harvesting because
there is a tendency for the pods to shatter upon reaching
maturity.
Among the legumes, the soybean, also classed as an oilseed, is
pre-eminent for its high (38–45%)
protein
content as well as its high (20%) oil content. Soybeans are the
second most valuable agricultural export in the United States
behind corn. The bulk of the soybean crop is grown for oil
production, with the high-protein defatted and "toasted" soy meal
used as livestock feed. A smaller percentage of soybeans are used
directly for human consumption.
Immature soybeans may be boiled whole in their green pod and served
with
salt, under the Japanese name .
Because of the proclaimed health benefits of soy,
edamame has been featured as an ideal snack
alternative in fitness and healthy living magazines. Edamame is
sold in the frozen vegetable section at some larger grocery stores,
and as ready-to-eat snackfood in many Asian delis.
In
China, Japan, and
Korea the bean and products made from the bean are a
popular part of the diet. The Chinese invented
tofu (豆腐), and also made use of several varieties of
soybean paste as seasonings. Japanese
foods made from soya include
miso
(味噌),
nattō (納豆),
kinako (黄粉) and
edamame (枝豆). In
Korean cuisine, soybean sprouts, called
kongnamul (
콩나물), are also used in a
variety of dishes, and are also the base ingredient in
doenjang,
cheonggukjang and
ganjang.
In Vietnam, soya bean
are used to make soybean paste- tương in the North with the most popular
products are tương Bần, tương Nam Đàn, tương
Cự Đà as a garnish of phở dish and
gỏi cuốn dish), tofu
(đậu hũ or đậu phụ or tàu hũ), soya
sauce (nước tương, literally: soya water), soya milk
(nước đậu in the North or sữa đậu nành in the
South), đậu hũ nước đường (tofu sweet soup).
In
India, black soybean is popular in the Himalayan regions
of the country (esp. Uttarakhand
), where it is consumed in various ways similar to
pulses.
The beans can be processed in a variety of ways. Common forms of
soy (or
soya) include
soy meal,
soy flour,
soy milk,
tofu,
textured vegetable protein (TVP,
which is made into a wide variety of
vegetarian foods, some of them intended to
imitate
meat),
tempeh,
soy
lecithin and
soybean
oil. Soybeans are also the primary ingredient involved in the
production of
soy sauce (or
shoyu).
Soybeans grow throughout Asia and
North and South America.
Soybean fields in the United
States
Archer Daniels Midland (ADM)
is among the largest processors of soybeans and soy products. ADM
along with
Dow Chemical
Company,
DuPont and
Monsanto Company support the industry trade
associations United Soybean Board and Soyfoods Association of North
America. These trade associations have increased the consumption of
soy products dramatically in recent years.
Oil
Soyabean seed contains about 19 % Oil. To Extract soybean oil from
seed , the soybeans are cracked, adjusted for moisture content,
rolled into flakes and solvent-extracted with commercial hexane.
The oil is then refined, blended for different applications, and
sometimes hydrogenated. Soybean oils, both liquid and partially
hydrogenated, are exported abroad, sold as "vegetable oil," or end
up in a wide variety of processed foods. The remaining soybean
husks are used mainly as animal feed.
Meal
Soybean meal is the material remaining after solvent extraction of
oil from soybean flakes, with a 50%
soy
protein content. The meal is 'toasted' (a
misnomer because the heat treatment is with moist
steam) and ground in a
hammer mill.
Soybean meal is an essential element of the American production
method of growing farm animals such as
poultry and
swine on an
industrial scale that began in the 1930s; and more recently the
aquaculture of
catfish. Ninety-eight percent of the U.S. soybean
crop is used for livestock feed. Soybean meal is also used in lower
end
dog foods.
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
Soy-based
infant formula (SBIF) is
used for lactose-intolerant infants and for infants who are
allergic to cow milk proteins. It is sold in powdered,
ready-to-feed, and concentrated liquid forms.
Some reviews have expressed the opinion that more research is
needed to determine what effect the phytoestrogens in soybeans may
have on infants. 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. One of these
studies, published in the Journal of Nutrition, 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 substitutes
Open package of a soy-based cream
cheese alternative with chives
Soybeans can be processed to produce a texture and appearance
similar to many other foods. For example, soybeans are the primary
ingredient in many
dairy product
substitutes (e.g.,
soy milk,
margarine,
soy ice
cream,
soy yogurt,
soy cheese, and soy cream cheese) and meat
substitutes (e.g.
veggie burgers).
These substitutes are readily available in most
supermarkets. Although soy milk does not
naturally contain significant amounts of digestable
calcium (the high calcium content of soybeans is
bound to the insoluble constituents and remains in the
soy pulp), many manufacturers of soy milk sell
calcium-enriched products as well. Soy is also used in
Tempeh: the beans (sometimes mixed with grain) are
fermented into a solid cake.
Soy products also are used as a low cost filler in meat and poultry
products. Food service, retail and institutional (primarily school
lunch and correctional) facilities regularly use such "extended"
products. Extension may result in diminished flavor, but fat and
cholesterol are reduced. Vitamin and mineral fortification can be
used to make soy products nutritionally equivalent to animal
protein; the protein quality is already roughly equivalent.
Other products
Soybeans are the bean used in Chinese fermented black beans,
douchi, not the sometimes confused
black turtle beans.
Soybeans are also used in industrial products including oils,
soap,
cosmetics,
resins,
plastics,
inks,
crayons,
solvents, and
clothing.
Soybean oil is the primary source of
biodiesel in the United States, accounting for 80%
of domestic biodiesel production. Soybeans have also been used
since 2001 as fermenting stock in the manufacture of a brand of
vodka.
Cattle feed
Cattle are often fed soy. Dairy cows feeding on spring grasses
instead of a grain ration of corn and soy have been shown to be
healthier, producing more milk all the while belching less
methane, a potent green-house gas linked to climate
change. Spring grasses are rich in Omega-3 fatty acids whereas soy
is predominantly Omega-6. "Cows fed plants like alfalfa and
flaxseed, substances that, unlike corn or soy, mimic the spring
grasses that the animal evolved long ago to eat."
Health benefits
Omega-3 fatty acids
Roasted soybeans
Omega-3 fatty acids, for
example,
alpha-linolenic acid
C18-3, all cis, 9,12,15 octadecatrienoic acid (where the omega-3
refers to carbon number 3 counting from the hydrocarbon tail
whereas C-15 refers to carbon number 15 counting from the carboxyl
acid head) are special fat components that benefit many body
functions. However, the effects which are beneficial to health are
associated mainly with the longer-chain, more unsaturated fatty
acids eicosapentaenoic (20:5n-3, EPA) and docosahexaenoic acid
(22:6n-3, DHA) found in fish oil and oily fish. For instance, EPA
and DHA, inhibit blood clotting, while there is no evidence that
alpha-linolenic acid (aLNA) can do this. Soybean oil is one of the
few common vegetable oils that contains a significant amount of
aLNA; others include
canola,
walnut,
hemp, and
flax. However, soybean oil does not contain EPA or DHA.
Soybean oil does contain significantly greater amount of
omega-6 fatty acids in the oil: 100g of soybean oil
contains 7g of omega-3 fatty acids to 51g of omega-6: a ratio of
1:7. Flaxseed, in comparison, has an omega-3:omega-6 ratio of
3:1.
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 do not have an enzyme, chalcone isomerase which converts a
flavone precursor into an isoflavone.
In contradiction to well known benefits of isoflavones, genistein
acts as an oxidant (stimulating nitrate synthesis), and blocks
formation of new blood vessels (antiangiogenic effect). Some
studies show that genistein acts as inhibitor of substances that
regulate cell division and cell survival (growth factors).
A review of the available studies by the United States
Health and Human Services Agency for Healthcare
Research and Quality (AHRQ) found little evidence of
substantial health improvements and no adverse effects, but also
noted that there was no long-term safety data on estrogenic effects
from soy consumption.
Cholesterol reduction
The dramatic increase in soyfood sales is largely credited to the
Food and Drug
Administration's (FDA) approval of soy as an official
cholesterol-lowering food, along with other heart and health
benefits. A 2001
literature review
argued that these health benefits were poorly supported by the
available evidence, and noted that disturbing data on soy's effect
on the cognitive function of the elderly existed. In 2008, an
epidemiological study of 719 Indonesian elderly found that tofu
intake was associated with worse memory, but
tempeh (a fermented soy product) intake was
associated with better memory. This study replicated other
studies.
From 1992 to 2003, sales have experienced a 15% compound annual growth rate, increasing from $300 million to $3.9 billion over 11 years, as new soyfood categories have been introduced, soyfoods have been repositioned in the market place, thanks to a better emphasis on marketing nutrition.
In 1995, the
New England Journal of Medicine (Vol. 333,
No. 5) published a meta-analysis financed by DuPont Protein
Technologies International (PTI), which produces and markets soy
through
The Solae
Company. The meta-analysis concluded that soy protein is
correlated with significant decreases in serum cholesterol,
LDL (bad cholesterol) and
triglycerides. However,
HDL(good cholesterol) did not
increase by a significant amount. Soy
phytoestrogens (
isoflavones: genistein and daidzein)
adsorbed onto the soy protein were suggested as the
agent reducing serum cholesterol levels. On the basis of this
research PTI filed a petition with FDA in 1998 for a health claim
that soy protein may reduce cholesterol and the risk of heart
disease.
The FDA granted the following health claim for soy: "25 grams of
soy protein a day, as part of a diet low in saturated fat and
cholesterol, may reduce the risk of heart disease." 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.
An American Heart Association review of a decade long study of soy
protein benefits casts doubt on the FDA allowed "Heart Healthy"
claim for soy protein and does not recommend isoflavone
supplementation. The review panel also found that soy isoflavones
have not been shown to reduce post menopause "hot flashes" in women
and the efficacy and safety of isoflavones to help prevent cancers
of the breast, uterus or prostate is in question.
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,
minimizing diabetes, and reducing inflammation. However, phytic
acid is also criticized for reducing vital minerals due to its
chelating effect, especially for diets already low in
minerals.
Health risks
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
should not 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 are among the richest foods in
total phytoestrogens (wet basis per 100g), which are present
primarily in the form of the isoflavones daidzein and
genistein.
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 to promote
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.
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.
Another analysis suggests an inverse association between total
polyunsaturated fatty acids and breast cancer risk.
Men
Because of the phytoestrogen content, some studies have suggested
that there is 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 has not been indicated by
any study; the popularity of the notion seems to be based on the
simplistic misapprehension that estrogen and testosterone have a
simple, inverse relationship in sexual hormone systems and
sex-related behaviour. Their interplay is very complicated and
largely still unknown.
A study published in April 2008 concluded that soy food intake has
an inverse association with sperm concentration in
fertility-deficient men. The same study found that soy intake does
not affect sperm motility, morphology, or ejaculate volume.
Allergy
Allergy to soy is often said to be rather common, and the food is
listed with other foods that commonly cause allergy, such as milk,
eggs, peanuts, tree nuts, shellfish. However, a critical review of
medical literature reveals surprisingly little solid information on
the topic. The problem has been reported amongst younger children
and the diagnosis of soy allergy is often based on symptoms
reported by parents and/or results of skin tests or blood tests for
allergy. Only a few reported studies have attempted to confirm
allergy to soy by direct challenge with the food under controlled
conditions. In these circumstances it is clear that skin/blood
tests considerably overestimate the problem, as do parental
reports. It is very difficult to give a reliable estimate of the
true prevalence of soy allergy in the general population. To the
extent that it does exist, soy allergy may cause cases of urticaria
(hives) and angioedema (swelling), usually within minutes to two
hours of ingestion of the food. In rare, severe cases true
anaphylaxis may occur, a condition that is much more common with
allergy to foods such as peanut and shellfish. The reason for the
discrepancy is likely that soy proteins, the causative factor in
allergy, are far less potent at triggering allergy symptoms than
the proteins of peanut and shellfish. An allergy test that is
positive demonstrates that the immune system has formed IgE
antibodies to soy proteins. However, when soy is ingested proteins
must evade digestion and be absorbed in a form capable of
triggering allergy and also in sufficient quantities to reach a
threshold to provoke actual symptoms. The low potency of soy
proteins as allergens may help explain why allergy skin/blood tests
suggest that soy allergy is common, yet few cases are confirmed
when the food is eaten under observation.
Soy can also trigger symptoms via
food
intolerance, a situation where no immunologic (allergic)
mechanism can be proven. One scenario is seen in very young infants
who have vomiting and diarrhoea when fed soy-based formula. The
symptoms resolve when the formula is withdrawn and recur when it is
re-administered. Older infants can suffer a more severe disorder
with vomiting, diarrhoea that may be bloody, anemia, weight loss
and failure to thrive. The most common cause of this unusual
disorder is a sensitivity to cow's milk, but there is no doubt that
soy formulas can also be the trigger. The precise mechanism is
unclear and it could be immunologic, although not through the
IgE-type antibodies that have the leading role in urticaria and
anaphylaxis. Fortunately it is also self-limiting and will often
disappear in the toddler years.
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 soybeans. The
common amounts of phytoestrogens in soy beans are not to be
compared to concentrated estrogen.
One study followed over 3000 Japanese men between 1965 and 1999, and that showed a
positive correlation between brain atrophy and consumption of
tofu. A study on elderly Indonesian men and women found that
tempeh consumption was independently related to better
memory.
Carcinogen
Raw
soy flour is known to cause
pancreatic cancer in rats. However,
studies suggest heated soy flour is not
carcinogenic in fat rats. Whether soy might
promote pancreatic cancer in humans is unknown because studies have
not yet attempted to single out soy intake and the incidence of
pancreatic cancer in humans. The doses of soy used to induce
pancreatic cancer in rats are said to be larger than humans would
normally consume. In the meantime, several epidemiologic studies
have found a
protective effect against pancreatic cancer
in high consumers of soy
and other foods typical of the
traditional Japanese and modern Seventh Day Adventist diet.
Existing cancer patients have been advised by the Cancer Council of
New South Wales, Australia to avoid high consumption of soy foods
and supplements because of conflicting evidence these may
accelerate the growth of hormone-dependent tumours. "While they
[soy foods] may have a protective effect, there is also some
evidence that phyto-oestrogens may stimulate the growth of existing
hormone-dependent cancers," according to a 2007 statement by the
council.
Soybean futures
Soybean
futures are traded on the Chicago
Board of Trade
and have delivery dates in January (F), March (H),
May (K), July (N), August (Q), September (U), November
(X).
It is also traded on other commodity futures exchanges under
different contract specifications:
Soy beans also come from Mack and Bewick in the city of
Detroit.
See also
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