Phytoestrogens are natural substances that are present in some plants and when ingested mimic the action of estrogen (female sex hormones). They are sometimes called “dietary estrogens”, they are a diverse group of naturally occurring non-steroidal plant compounds that, due to their structural similarity to estradiol (17-β-estradiol), have the ability to cause estrogenic or antiestrogenic effects. Phytoestrogens are not nutrients, as their absence in the diet does not cause disease, and they are not known to be involved in any normal biological functions.
The name comes from the Greek phyto (“plant”), and estrogen – a hormone that ensures the fertility of female mammals. The word “estrus” means sexual desire, and “gene” – to generate.
It has been suggested that plants use phytoestrogens as part of their natural defenses by influencing the fertility of female herbivores and controlling their overpopulation.
Similarities at the molecular level allow phytoestrogens to gently mimic estrogens, and sometimes to act as their antagonists (weaken the effect on the receptor, and hence the body). Phytoestrogens were first discovered in 1926, but it was unclear whether they could have some effect on human and animal metabolism.
Chemical structure
Phytoestrogenic substances mainly belong to a large group of substituted natural phenolic compounds. Kumestan, prenylflavonoids and isoflavones are the three most active estrogenic compounds in this class. The most studied are isoflavones, which are commonly found in soybeans and red clover.
Lignans have also been identified as phytoestrogens, although they are not flavonoids.
Mycoestrogens have similar structures and effects, but are not components of plants, they are form metabolites of molds of the genus Fusarium, which are especially common in cereals, but also found in other places, such as various forage crops. However, mycoestrogens are rarely taken into account when discussing phytoestrogens.
Mechanism of action
Phytoestrogens primarily affect binding to estrogen receptors (ERs). There are two types of estrogen receptors: alpha (EP-α) and beta (EP-β) – and many phytoestrogens have a slightly higher affinity for EP-β compared to EP-α.
The key structural elements that allow phytoestrogens to bind with high affinity for estrogen receptors and demonstrate estradiol-like effects are:
- phenolic ring, which is necessary for binding to the estrogen receptor
- An isoflavone ring that mimics the estrogen ring at the receptor binding site
- Low molecular weight similar to estrogen (Mr = 272)
- The distance between two hydroxyl groups on the nucleus of isoflavones is like estradiol
- The optimal picture of hydroxylation
In addition to interacting with EPs, phytoestrogens can also modulate the concentration of endogenous estrogens by binding or inactivating certain enzymes, as well as affecting the bioavailability of sex hormones by suppressing or stimulating the synthesis of sex hormone binding globulin (SHBG).
New data show that some phytoestrogens bind to receptor transactivators that are activated by peroxisome proliferators (PPARs). In vitro studies show activation of PPARs at concentrations above 1 μm, which exceeds the level of EP activation. At concentrations below 1 μmol, EP activation may play a dominant role. At higher concentrations (> 1 μmol) both EP and PPARs are activated. Studies have shown that both EP and PPARs affect each other and thus contribute to different dose-dependent effects. The final biological effect is determined by the balance between these pleiotropic actions.
Role in ecology
These compounds in plants are an important part of their defense system, mainly against fungi.
Phytoestrogens are ancient natural substances, and it is believed that in terms of the content of dietary phytochemicals, they evolved with mammals. For humans, phytoestrogens are not the only external source of “estrogen-like” substances. Xenoestrogens (modern, synthetic compounds) are found as food additives and ingredients in cosmetics, plastics and insecticides. Ecologically, they have a similar effect to phytoestrogens, which makes it difficult to clearly separate the two types of agents in studies of populations.
Research with birds
It was found that the consumption of plants with unusual phytoestrogens in drought, reduces fertility in quail. Food for parrots, available in nature, showed only weak estrogenic activity. Studies have been conducted with the use of complementary foods containing phytoestrogens to reproduce endangered species.
Which foods have the most phytoestrogens?
According to one study of nine common phytoestrogens in the Western diet, foods with a relatively high content of phytoestrogens are nuts and oilseeds, followed by soybeans, cereals and bread, legumes, meat, soy products, vegetables, fruits, alcoholic and soft drinks. Flax and other oilseeds had the highest phytoestrogen content, followed by soybeans and tofu.
The highest concentrations of isoflavones are found in soy products and then in legumes, while lignans are the main source of phytoestrogens found in nuts and oilseeds (eg flax). They are also found in cereals, legumes, fruits and vegetables.
The content of phytoestrogens differs in different foods and can differ significantly within one of their groups (eg, soy drinks, tofu, depending on the processing mechanisms and type of soybeans). Legumes (especially soybeans), whole grains and some seeds are high in phytoestrogens.
A more complete list of products that are known to contain phytoestrogens includes:
- Soybeans and soy products
- Linen
- Sesame seeds
- Wheat
- Oat
- Barley
- Bean
- Lentil
- Rice
- Alfalfa
- Mash abo chapter mung
- Apples
- Carrot
- Garnet
- Wheat germ
- Rice bran
- Lupine
- Kudzu
- Coffee
- Licorice root
- Ginseng
- Hop
- Bourbon
- Beer
- Fennel
- Anise
- Red clover
An epidemiological study of women in the United States found that the recommended daily intake of phytoestrogens for healthy Caucasian women in the postmenopausal period is less than one milligram per day.
Impact on people
In the human body, phytoestrogens are easily absorbed, circulating in plasma and excreted in the urine. A wide range of beneficial effects of phytoestrogens on the cardiovascular, metabolic, central nervous system, as well as in terms of reducing the risk of cancer and symptoms in the postmenopausal period.
However, there are also concerns that phytoestrogens may act as substances that adversely affect the hormonal system and health (endocrine disruptors). Based on the available evidence, it is unclear whether the potential health benefits of phytoestrogens outweigh their risks.
Men
It is unclear whether phytoestrogens affect male sexuality, and there are conflicting results regarding the potential effects of isoflavones in soy products.
In 2010, a meta-analysis of fifteen placebo-controlled studies showed that “neither soy products nor isoflavone supplements alter the bioavailable testosterone levels in men.” Some studies have shown that adding isoflavones to the diet does not affect sperm concentration, quantity or motility, and has no effect on testicular or ejaculate volume.
Decreased sperm count and increased testicular cancer in the West may be due to the higher presence of isoflavone phytoestrogens in the diet, but this association has not been conclusively proven. In addition, there is some evidence that phytoestrogens may affect male fertility.
Women
It is not clear whether phytoestrogens affect the cause of cancer in women and have an effect in its prevention. Some epidemiological studies have shown a protective effect against breast cancer. Others have shown that consuming soy estrogen is safe for patients with breast cancer and can reduce mortality and recurrence rates.
It remains unclear whether phytoestrogens can minimize some of the negative effects of low estrogen levels (hypoestrogenism) resulting from orectomy, menopause and other causes.
The Cochrane Reviews on the use of phytoestrogens to relieve vasomotor symptoms of menopause (hot flashes) notes that there is no comprehensive evidence to support the possible benefits of using these compounds for this purpose, although the effects of genistein should be studied further.
Newborns
Some studies have shown that isoflavone concentrations can affect intestinal cells. At low doses, genistein acted as a weak estrogen and stimulated cell growth; at high doses, it suppressed proliferation (cell division) and changed the dynamics of cell cycles.
Some papers suggest that more research is needed to answer the question of what effects phytoestrogens can have on children. However, their authors did not find any adverse effects.
Studies show that there is no negative impact on human growth, development or reproduction due to the consumption of soy formula compared to regular cow’s milk. The American Academy of Pediatrics states:
“Although infant formulas based on purified soy protein (isolate) can be used to provide nutrition for normal growth and development, there is little evidence for their use instead of the formula based on cow’s milk. These indications include: for children with galactosemia and hereditary lactose deficiency (rare) in situations where a vegetarian diet is best.
In folk medicine
In some countries, phytoestrogens have been used for centuries to treat menstrual and menopausal disorders, as well as fertility problems. Plants used that have been found to contain phytoestrogens include Pueraria Mirifica and its close relative Pueraria lobica (kudzu), as well as bagpipe, fennel and anise.
A careful study of one such source of phytoestrogen, meadow clover, has shown that its use is safe but ineffective in relieving menopausal symptoms. For example, buckthorn is effective in menopause, PMS and other gynecological disorders, but does not contain phytoestrogens. Ginseng contains phytoestrogens and is also used to relieve menopausal symptoms.
