Phytoestrogens
Encyclopedia
Phytoestrogens are plant-derived xenoestrogen
s functioning as the primary female
sex hormone (see estrogen
) not generated within the endocrine system
but consumed by eating phytoestrogonic plants. Also called "dietary estrogens", they are a diverse group of naturally occurring nonsteroidal plant compounds that, because of their structural similarity with estradiol
(17-β-estradiol), have the ability to cause estrogenic or/and antiestrogenic effects. It has been proposed that plants use the phytoestrogens as part of their natural defence against the overpopulation of the herbivore animals by controlling the male fertility.
Their name comes from the Greek
phyto = plant and estrogen, the hormone which gives fertility to the female mammals. The word "estrus" -Greek οίστρος- means sexual desire and "gene" -Greek γόνο- is "to generate").
The similarities, at molecular level, of estrogens and phytoestrogens allow them to mildly mimic and sometimes act as antagonists of estrogen
. Phytoestrogens were first observed in 1926, but it was unknown if they could have any effect in human or animal metabolism. In the 1940s it was noticed for the first time that red clover
(a phytoestrogens-rich plant) pastures had effects on the fertility of grazing sheep. Researchers are exploring the nutrition
al role of these substances in the regulation of cholesterol
, and the maintenance of proper bone density post-menopause
. Evidence is accruing that phytoestrogens may have protective action against diverse health disorders, such as prostate
, breast
, bowel, and other cancer
s, cardiovascular disease, brain
function disorders and osteoporosis
, though there is no evidence to support their use in alleviating the symptoms of menopause.
Phytoestrogens cannot be considered as nutrients, given that the lack of these in diet does not produce any characteristic deficiency syndrome, nor do they participate in any essential biological function.
Analytical methods are available to determine phytoestrogen content in plants and food.
ic compounds : the coumestan
s, prenylated flavonoid
s and isoflavone
s are three of the most active in estrogenic effects in this class. The best-researched are isoflavones, which are commonly found in soy and red clover
. Lignan
s have also been identified as phytoestrogens, although they are not flavonoids. Mycoestrogens
have similar structures and effects, but are not components of plants; these are mold metabolites of Fusarium
, a fungus that is frequently found in pastures as well as in alfalfa
and clover. Although mycoestrogens are rarely taken into account in discussions about phytoestrogens, these are the compounds that initially generated the interest on the topic.
s (ER). There are two variants of the estrogen receptor, alpha (ER-α
) and beta (ER-β
) and many phytoestrogens display somewhat higher affinity for ER-β compared to ER-α.
The key structural elements that enable phytoestrogens to bind with high affinity to estrogen receptors and display estradiol-like effects are:
In addition to interaction with ERs, phytoestrogens may also modulate the concentration of endogenous estrogens by binding or inactivating some enzymes, and may affect the bioavailability of sex hormones by binding or stimulating the synthesis of sex hormone binding globuline (SHBG).
Emerging evidence shows that some phytoestrogens bind to and transactivate peroxisome proliferator-activated receptor
s (PPARs). In vitro studies show an activation of PPARs at concentrations above 1 μM, which is higher than the activation level of ERs. At the concentration below 1 μM, activation of ERs may play a dominate role. At higher concentrations (>1 μM), both ERs and PPARs are activated. Studies have shown that both ERs and PPARs influence each other and therefore induce differential effects in a dose-dependent way. The final biological effects of genistein are determined by the balance among these pleiotrophic actions.
Phytoestrogens are ancient naturally occurring substances, and as dietary phytochemicals they are considered as co-evolutive with mammals. In the human diet, phytoestrogens are not the only source of exogenous estrogens. Xenoestrogens (novel, man-made), are found as food additive
s and ingredients, and also in cosmetics, plastics, and insecticides. Environmentally, they have similar effects as phytoestrogens, making it difficult to clearly separate the action of these two kind of agents in studies done on populations.
seed and other oilseeds contained the highest total phytoestrogen content, followed by soybeans and tofu
. The highest concentrations of isoflavones are found in soybeans and soybean products followed by legumes, whereas lignans are the primary source of phytoestrogens found in nuts and oilseeds (e.g. flax) and also found in cereals, legumes, fruits and vegetables.
Phytoestrogen content varies in different foods, and may vary significantly within the same group of foods (e.g. soy beverages, tofu) depending on processing mechanisms and type of soybean used. Legumes (in particular soybeans), whole grain cereals, and some seeds are high in phytoestrogens.
A more comprehensive list of foods known to contain phytoestrogens includes:
soybeans,
tofu,
tempeh
,
soy beverages,
linseed (flax),
sesame
seeds,
wheat
berries,
fenugreek
,
oat
s,
barley
,
dried bean
s,
lentil
s,
yams
,
rice
,
alfalfa
,
mung bean
s,
apple
s,
carrot
s,
pomegranate
s,
wheat germ,
rice bran,
soy linseed bread,
ginseng
, hops
,
bourbon
, beer
,
fennel
and anise
.
An epidemiological study of women in the United States found that the dietary intake of phytoestrogens in healthy post-menopausal Caucasian women is less than one milligram daily.
In the last few years, there has been a great deal of research into the possible beneficial effects of phytoestrogens in both diabetes and coronary heart disease.
concentrations in men." Furthermore, Isoflavones supplementation has no effect on sperm concentration, count or motility, and show no changes in testicular or ejaculate volume.
, and protective effects were found with larger concentrations of the same phytoestrogen. A 2006 review article stated the opinion that not enough information is available, and that even if isoflavones have mechanisms to inhibit tumor growth, in vitro results justify the need to evaluate, at cellular level, the impact of isoflavones on breast tissue in females at high risk for breast cancer. Recent epidemiologic studies suggest that consumption of soy estrogens is safe for patients with breast cancer, and may decrease mortality and recurrence rates. A Cochrane Review
of the use of phytoestrogens to relieve the vasomotor symptoms of menopause (hot flashes) demonstrated that there was no evidence to suggest any benefit to their use. It has been reported that phytoestrogens such as genistein
may help prevent photoaging in human skin, and also promote formation of hyaluronic acid.
HRT may also be effective at reversing the effects of aging on muscle. A future aim is to target therapy to molecular mechanisms that work specifically in selected tissues.
Some reviews express the opinion that more research is needed to answer the question of what effect phytoestrogens may have on infants, but their authors did not find any adverse effects. Multiple studies conclude there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy-based infant formula compared to conventional cow-milk formula. While it should be noted that all infant formulas are inferior to human milk, soy formula presents no more risk than cow-milk formula. One of these studies, published at the Journal of Nutrition, concludes that:
Clinical guidelines from the American Academy of Pediatrics
state: "although isolated soy protein-based
formulas may be used to provide nutrition for normal
growth and development, there are few indications
for their use in place of cow milk-based formula.
These indications include (a) for infants with galactosemia
and hereditary lactase deficiency (rare) and
(b) in situations in which a vegetarian diet is preferred."
mirifica, and its close relative, kudzu
, Angelica
, fennel
and anise
.
In a rigorous study, the use of one such source of phytoestrogen, red clover, has been shown to be safe, but ineffective in relieving menopausal symptoms (black cohosh is also used for menopausal symptoms, but does not contain phytoestrogens.)
Xenoestrogen
Xenoestrogens are a type of xenohormone that imitates estrogen. They are widely used industrial compounds such as PCB, BPA and Phthalates, that have estrogenic effects on a living organism even though they differ chemically from the naturally occurring estrogenic substances internally produced by...
s functioning as the primary female
Female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
sex hormone (see estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
) not generated within the endocrine system
Endocrine system
In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...
but consumed by eating phytoestrogonic plants. Also called "dietary estrogens", they are a diverse group of naturally occurring nonsteroidal plant compounds that, because of their structural similarity with estradiol
Estradiol
Estradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
(17-β-estradiol), have the ability to cause estrogenic or/and antiestrogenic effects. It has been proposed that plants use the phytoestrogens as part of their natural defence against the overpopulation of the herbivore animals by controlling the male fertility.
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
phyto = plant and estrogen, the hormone which gives fertility to the female mammals. The word "estrus" -Greek οίστρος- means sexual desire and "gene" -Greek γόνο- is "to generate").
The similarities, at molecular level, of estrogens and phytoestrogens allow them to mildly mimic and sometimes act as antagonists of estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
. Phytoestrogens were first observed in 1926, but it was unknown if they could have any effect in human or animal metabolism. In the 1940s it was noticed for the first time that red clover
Red clover
Trifolium pratense is a species of clover, native to Europe, Western Asia and northwest Africa, but planted and naturalised in many other regions....
(a phytoestrogens-rich plant) pastures had effects on the fertility of grazing sheep. Researchers are exploring the nutrition
Nutrition
Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....
al role of these substances in the regulation of cholesterol
Cholesterol
Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
, and the maintenance of proper bone density post-menopause
Menopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...
. Evidence is accruing that phytoestrogens may have protective action against diverse health disorders, such as prostate
Prostate
The prostate is a compound tubuloalveolar exocrine gland of the male reproductive system in most mammals....
, breast
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
, bowel, and other cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
s, cardiovascular disease, brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
function disorders and osteoporosis
Osteoporosis
Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...
, though there is no evidence to support their use in alleviating the symptoms of menopause.
Phytoestrogens cannot be considered as nutrients, given that the lack of these in diet does not produce any characteristic deficiency syndrome, nor do they participate in any essential biological function.
Analytical methods are available to determine phytoestrogen content in plants and food.
Structure
Phytoestrogens mainly belong to a large group of substituted natural phenolNatural phenol
Natural phenols, bioavailable phenols, plant phenolics, low molecular weight phenols or phenoloids are a class of natural products. They are small molecules containing one or more phenolic group. These molecules are smaller in size than polyphenols, containing less than 12 phenolic groups...
ic compounds : the coumestan
Coumestan
Coumestan is an organic compound that is a derivative of coumarin. Coumestan forms the central core of a variety of natural compounds known collectively as coumestans. Coumestans, including coumestrol, a phytoestrogen, are found in a variety of plants...
s, prenylated flavonoid
Prenylated flavonoid
Prenylated favonoids are a sub-class of flavonoids. They are widely distributed throughout the plant kingdom. Some are known to have phytoestrogenic or antioxidant properties. They are given in the list of adaptogens in herbalism....
s and isoflavone
Isoflavone
Isoflavones comprise a class of organic compounds, often naturally occurring, related to the isoflavonoids. Many act as phytoestrogens in mammals...
s are three of the most active in estrogenic effects in this class. The best-researched are isoflavones, which are commonly found in soy and red clover
Red clover
Trifolium pratense is a species of clover, native to Europe, Western Asia and northwest Africa, but planted and naturalised in many other regions....
. Lignan
Lignan
The lignans are a group of chemical compounds found in plants. Lignans are one of the major classes of phytoestrogens, which are estrogen-like chemicals and also act as antioxidants. The other classes of phytoestrogens are the isoflavones and coumestans...
s have also been identified as phytoestrogens, although they are not flavonoids. Mycoestrogens
Mycoestrogens
Mycoestrogens are estrogens produced by fungi. The most important mycoestrogen is zearalenone, produced by Fusarium species of fungi. Zearalenone is the main phyto-oestrogen consumed in the USA. It may be one dietary factor that can reduce the prevalence of breast cancer.-In Food:Mycoestrogens...
have similar structures and effects, but are not components of plants; these are mold metabolites of Fusarium
Fusarium
Fusarium is a large genus of filamentous fungi widely distributed in soil and in association with plants. Most species are harmless saprobes, and are relatively abundant members of the soil microbial community. Some species produce mycotoxins in cereal crops that can affect human and animal health...
, a fungus that is frequently found in pastures as well as in alfalfa
Alfalfa
Alfalfa is a flowering plant in the pea family Fabaceae cultivated as an important forage crop in the US, Canada, Argentina, France, Australia, the Middle East, South Africa, and many other countries. It is known as lucerne in the UK, France, Australia, South Africa and New Zealand, and known as...
and clover. Although mycoestrogens are rarely taken into account in discussions about phytoestrogens, these are the compounds that initially generated the interest on the topic.
Mechanism of action
Phytoestrogens exert their effects primarily through binding to estrogen receptorEstrogen receptor
Estrogen receptor refers to a group of receptors that are activated by the hormone 17β-estradiol . Two types of estrogen receptor exist: ER, which is a member of the nuclear hormone family of intracellular receptors, and the estrogen G protein-coupled receptor GPR30 , which is a G protein-coupled...
s (ER). There are two variants of the estrogen receptor, alpha (ER-α
Estrogen receptor alpha
Estrogen receptor alpha , also known as NR3A1 , is a nuclear receptor that is activated by the sex hormone estrogen...
) and beta (ER-β
Estrogen receptor beta
Estrogen receptor beta , also known as NR3A2 , is a nuclear receptor which is activated by the sex hormone estrogen. In humans, ER-β is encoded by the ESR2 gene.- Function :...
) and many phytoestrogens display somewhat higher affinity for ER-β compared to ER-α.
The key structural elements that enable phytoestrogens to bind with high affinity to estrogen receptors and display estradiol-like effects are:
- The phenolic ring that is indispensable for binding to estrogen receptor
- The ring of isoflavones mimicking a ring of estrogens at the receptors binding site
- Low molecular weight similar to estrogens (MW=272)
- Distance between two hydroxyl groups at the isoflavones nucleus similar to that occurring in estradiol
- Optimal hydroxylation pattern
In addition to interaction with ERs, phytoestrogens may also modulate the concentration of endogenous estrogens by binding or inactivating some enzymes, and may affect the bioavailability of sex hormones by binding or stimulating the synthesis of sex hormone binding globuline (SHBG).
Emerging evidence shows that some phytoestrogens bind to and transactivate peroxisome proliferator-activated receptor
Peroxisome proliferator-activated receptor
In the field of molecular biology, the peroxisome proliferator-activated receptors are a group of nuclear receptor proteins that function as transcription factors regulating the expression of genes...
s (PPARs). In vitro studies show an activation of PPARs at concentrations above 1 μM, which is higher than the activation level of ERs. At the concentration below 1 μM, activation of ERs may play a dominate role. At higher concentrations (>1 μM), both ERs and PPARs are activated. Studies have shown that both ERs and PPARs influence each other and therefore induce differential effects in a dose-dependent way. The final biological effects of genistein are determined by the balance among these pleiotrophic actions.
Ecology
These compounds in plants are an important part of their defense system, mainly against fungi.Phytoestrogens are ancient naturally occurring substances, and as dietary phytochemicals they are considered as co-evolutive with mammals. In the human diet, phytoestrogens are not the only source of exogenous estrogens. Xenoestrogens (novel, man-made), are found as food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...
s and ingredients, and also in cosmetics, plastics, and insecticides. Environmentally, they have similar effects as phytoestrogens, making it difficult to clearly separate the action of these two kind of agents in studies done on populations.
Avian studies
The consumption of plants with unusual content of phytoestrogens under drought conditions, has been shown to decrease fertility in quail. Parrot food as available in nature has shown only weak estrogenic activity. Studies have been conducted on screening methods for environmental estrogens present in manufactured supplementary food, with the purpose to enable reproduction of endangered species.Food sources
According to a study by Canadian researchers about the content of nine common phytoestrogens in a Western diet, foods with the highest relative phytoestrogen content were nuts and oilseeds, followed by soy products, cereals and breads, legumes, meat products, and other processed foods that may contain soy, vegetables, fruits, alcoholic, and nonalcoholic beverages. FlaxFlax
Flax is a member of the genus Linum in the family Linaceae. It is native to the region extending from the eastern Mediterranean to India and was probably first domesticated in the Fertile Crescent...
seed and other oilseeds contained the highest total phytoestrogen content, followed by soybeans and tofu
Tofu
is a food made by coagulating soy milk and then pressing the resulting curds into soft white blocks. It is part of East Asian and Southeast Asian cuisine such as Chinese, Japanese, Korean, Indonesian, Vietnamese, and others. There are many different varieties of tofu, including fresh tofu and tofu...
. The highest concentrations of isoflavones are found in soybeans and soybean products followed by legumes, whereas lignans are the primary source of phytoestrogens found in nuts and oilseeds (e.g. flax) and also found in cereals, legumes, fruits and vegetables.
Phytoestrogen content varies in different foods, and may vary significantly within the same group of foods (e.g. soy beverages, tofu) depending on processing mechanisms and type of soybean used. Legumes (in particular soybeans), whole grain cereals, and some seeds are high in phytoestrogens.
A more comprehensive list of foods known to contain phytoestrogens includes:
soybeans,
tofu,
tempeh
Tempeh
Tempeh , or tempe , is a traditional soy product originally from Indonesia. It is made by a natural culturing and controlled fermentation process that binds soybeans into a cake form, similar to a very firm vegetarian burger patty...
,
soy beverages,
linseed (flax),
sesame
Sesame
Sesame is a flowering plant in the genus Sesamum. Numerous wild relatives occur in Africa and a smaller number in India. It is widely naturalized in tropical regions around the world and is cultivated for its edible seeds, which grow in pods....
seeds,
wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
berries,
fenugreek
Fenugreek
Fenugreek is a plant in the family Fabaceae. Fenugreek is used both as a herb and as a spice . The leaves and sprouts are also eaten as vegetables...
,
oat
Oat
The common oat is a species of cereal grain grown for its seed, which is known by the same name . While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed...
s,
barley
Barley
Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...
,
dried bean
Bean
Bean is a common name for large plant seeds of several genera of the family Fabaceae used for human food or animal feed....
s,
lentil
Lentil
The lentil is an edible pulse. It is a bushy annual plant of the legume family, grown for its lens-shaped seeds...
s,
yams
Yam (vegetable)
Yam is the common name for some species in the genus Dioscorea . These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania...
,
rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
,
alfalfa
Alfalfa
Alfalfa is a flowering plant in the pea family Fabaceae cultivated as an important forage crop in the US, Canada, Argentina, France, Australia, the Middle East, South Africa, and many other countries. It is known as lucerne in the UK, France, Australia, South Africa and New Zealand, and known as...
,
mung bean
Mung bean
The mung bean is the seed of Vigna radiata. It is native to the Indian subcontinent.-Description:They are small, ovoid in shape, and green in color...
s,
apple
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
s,
carrot
Carrot
The carrot is a root vegetable, usually orange in colour, though purple, red, white, and yellow varieties exist. It has a crisp texture when fresh...
s,
pomegranate
Pomegranate
The pomegranate , Punica granatum, is a fruit-bearing deciduous shrub or small tree growing between five and eight meters tall.Native to the area of modern day Iran, the pomegranate has been cultivated in the Caucasus since ancient times. From there it spread to Asian areas such as the Caucasus as...
s,
wheat germ,
rice bran,
soy linseed bread,
ginseng
Ginseng
Ginseng is any one of eleven species of slow-growing perennial plants with fleshy roots, belonging to the genus Panax of the family Araliaceae....
, hops
Hops
Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...
,
bourbon
Bourbon whiskey
Bourbon is a type of American whiskey – a barrel-aged distilled spirit made primarily from corn. The name of the spirit derives from its historical association with an area known as Old Bourbon, around what is now Bourbon County, Kentucky . It has been produced since the 18th century...
, beer
Beer
Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...
,
fennel
Fennel
Fennel is a plant species in the genus Foeniculum . It is a member of the family Apiaceae . It is a hardy, perennial, umbelliferous herb, with yellow flowers and feathery leaves...
and anise
Anise
Anise , Pimpinella anisum, also called aniseed, is a flowering plant in the family Apiaceae native to the eastern Mediterranean region and Southwest Asia. Its flavor resembles that of liquorice, fennel, and tarragon.- Biology :...
.
An epidemiological study of women in the United States found that the dietary intake of phytoestrogens in healthy post-menopausal Caucasian women is less than one milligram daily.
Health risks and benefits
In human beings, phytoestrogens are readily absorbed, circulate in plasma and are excreted in the urine. Metabolic influence is different from that of grazing animals due to the differences between ruminant versus monogastric digestive systems.In the last few years, there has been a great deal of research into the possible beneficial effects of phytoestrogens in both diabetes and coronary heart disease.
Males
A 2010 meta-analysis of fifteen placebo-controlled studies said that "neither soy foods nor isoflavone supplements alter measures of bioavailable testosteroneTestosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
concentrations in men." Furthermore, Isoflavones supplementation has no effect on sperm concentration, count or motility, and show no changes in testicular or ejaculate volume.
Females
There are conflicting studies, and it is unclear if phytoestrogens have any effect on the cause or prevention of cancer in females. Epidemiological studies showed a protective effect against breast cancer. In vitro studies concluded that females with current or past breast cancer should be aware of the risks of potential tumor growth when taking soy products, as they can stimulate the growth of estrogen receptor-positive cells in vitro. The potential for tumor growth was found related only with small concentration of genisteinGenistein
Genistein is one of several known isoflavones. Isoflavones, such as genistein and daidzein, are found in a number of plants including lupin, fava beans, soybeans, kudzu, and psoralea being the primary food source, also in the medicinal plant, Flemingia vestita and coffee Besides functioning as...
, and protective effects were found with larger concentrations of the same phytoestrogen. A 2006 review article stated the opinion that not enough information is available, and that even if isoflavones have mechanisms to inhibit tumor growth, in vitro results justify the need to evaluate, at cellular level, the impact of isoflavones on breast tissue in females at high risk for breast cancer. Recent epidemiologic studies suggest that consumption of soy estrogens is safe for patients with breast cancer, and may decrease mortality and recurrence rates. A Cochrane Review
Cochrane Library
The Cochrane Library is a collection of databases in medicine and other healthcare specialties provided by the Cochrane Collaboration and other organisations. At its core is the collection of Cochrane Reviews, a database of systematic reviews and meta-analyses which summarize and interpret the...
of the use of phytoestrogens to relieve the vasomotor symptoms of menopause (hot flashes) demonstrated that there was no evidence to suggest any benefit to their use. It has been reported that phytoestrogens such as genistein
Genistein
Genistein is one of several known isoflavones. Isoflavones, such as genistein and daidzein, are found in a number of plants including lupin, fava beans, soybeans, kudzu, and psoralea being the primary food source, also in the medicinal plant, Flemingia vestita and coffee Besides functioning as...
may help prevent photoaging in human skin, and also promote formation of hyaluronic acid.
HRT may also be effective at reversing the effects of aging on muscle. A future aim is to target therapy to molecular mechanisms that work specifically in selected tissues.
Infant formula
Some studies have found that some concentrations of isoflavones may have effects on intestinal cells. At low doses, genistein acted as a weak estrogen and stimulated cell growth; at high doses, it inhibited proliferation and altered cell cycle dynamics. This biphasic response correlates with how genistein is thought to exert its effects.Some reviews express the opinion that more research is needed to answer the question of what effect phytoestrogens may have on infants, but their authors did not find any adverse effects. Multiple studies conclude there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy-based infant formula compared to conventional cow-milk formula. While it should be noted that all infant formulas are inferior to human milk, soy formula presents no more risk than cow-milk formula. One of these studies, published at the Journal of Nutrition, concludes that:
"Comprehensive literature reviews and clinical studies of infants fed SBIFs [soy-based infant formulas] have resolved questions or raise 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"
Clinical guidelines from the American Academy of Pediatrics
American Academy of Pediatrics
The American Academy of Pediatrics is the major professional association of pediatricians in the United States. The AAP was founded in 1930 by 35 pediatricians to address pediatric healthcare standards. It currently has 60,000 members in primary care and sub-specialist areas...
state: "although isolated soy protein-based
formulas may be used to provide nutrition for normal
growth and development, there are few indications
for their use in place of cow milk-based formula.
These indications include (a) for infants with galactosemia
and hereditary lactase deficiency (rare) and
(b) in situations in which a vegetarian diet is preferred."
Ethnopharmacology
In some countries, phytoestrogenic plants have been used for centuries in the treatment of menstrual and menopausal problems, as well as for fertility problems. Plants used that have been shown to contain phytoestrogens include PuerariaPueraria
Pueraria is a genus of 15–20 species of plants native to Asia.The genus is polyphyletic, with different species being related to species in Glycine , Amphicarpaea, Nogra, Teyleria, Neonotonia, Pseudovigna, Pseudeminia, Pachyrhizus , and other genera of the tribe Phaseoleae.- Species :The...
mirifica, and its close relative, kudzu
Kudzu
Kudzu is a plant in the genus Pueraria in the pea family Fabaceae, subfamily Faboideae. It is a climbing, coiling, and trailing vine native to southern Japan and southeast China. Its name comes from the Japanese name for the plant, . It is a weed that climbs over trees or shrubs and grows so...
, Angelica
Angelica
Angelica is a genus of about 60 species of tall biennial and perennial herbs in the family Apiaceae, native to temperate and subarctic regions of the Northern Hemisphere, reaching as far North as Iceland and Lapland...
, fennel
Fennel
Fennel is a plant species in the genus Foeniculum . It is a member of the family Apiaceae . It is a hardy, perennial, umbelliferous herb, with yellow flowers and feathery leaves...
and anise
Anise
Anise , Pimpinella anisum, also called aniseed, is a flowering plant in the family Apiaceae native to the eastern Mediterranean region and Southwest Asia. Its flavor resembles that of liquorice, fennel, and tarragon.- Biology :...
.
In a rigorous study, the use of one such source of phytoestrogen, red clover, has been shown to be safe, but ineffective in relieving menopausal symptoms (black cohosh is also used for menopausal symptoms, but does not contain phytoestrogens.)
External links
- Phytoestrogen food sources
- Phytoestrogen content in food
- Phytoestrogens at e.hormone, a website of the Tulane/Xavier Center for Bioenvironmental Research