IngredientsA phytoestrogen is a plant-derived xenoestrogen — a type of estrogen produced by organisms other than humans — not generated within the endocrine system but consumed through eating plants or manufactured foods. Also called a "dietary estrogen," it is a diverse group of naturally occurring nonsteroidal plant compounds that, because of their structural similarity to estradiol (17-β-estradiol), have the ability to cause both estrogenic and antiestrogenic effects. Phytoestrogens represent polyphenolic and non-steroidal compounds that have a similar structure and biological activity to human estrogens, and are plant secondary metabolites widespread in over 300 various plant species.
Phytoestrogens are naturally occurring nonsteroidal phenolic plant compounds and can be divided into two main groups: flavonoids and non-flavonoids. Flavonoids include isoflavones, coumestans, and prenylflavonoids, and non-flavonoids include lignans. Additional subclasses recognized in the literature include stilbenes, chalcones, and flavones. The most abundant, most studied, and most potent phytoestrogens are isoflavones.
Phytoestrogens are natural chemical compounds contained in fruits, vegetables, legumes, whole grains, and especially flaxseed, clover, and soy products. They are generally found in soybeans (Glycine max L.), red clover (Trifolium pratense), and white clover (Trifolium repens L.). Other dietary sources include hops, beer, apples, onions, parsley, capsicum pepper, and tofu. Common foods containing phytoestrogens are soybeans and soy protein concentrate, miso, tempeh, and tofu. Some soy-based infant formulas manufactured with soy protein contain isoflavones.
Phytoestrogens are plant-produced bioactive secondary metabolites known to play an integral role in plant defense that frequently accumulate in times of stress and/or microbial infection.
Phytoestrogens are plant-derived compounds primarily found in soy products, and at lower levels in legumes, fruits, vegetables, nuts, and coffee. They are also consumed as over-the-counter supplements. Supplement forms available commercially include standardized soy isoflavone extracts (aglycone or glycoside form), red clover isoflavone extracts (standardized to formononetin, biochanin A, genistein, and daidzein), flaxseed lignans (secoisolariciresinol diglucoside, SDG), and whole soy protein isolates. Glycoside O and C forms of isoflavonoids are poorly absorbed in the intestine; they are converted by bacterial esterases and/or β-glycosidase enzymes to aglycones, which are absorbed more efficiently.
In some countries, phytoestrogenic plants have been used historically in the belief they can treat menstrual, menopausal, and fertility effects. Medicinal herbs containing phytoestrogens have a long history of use in traditional medicine and were officially discovered in the late 1800s.
In Traditional Chinese Medicine, several herbs rich in phytoestrogens are used to prevent and cure various diseases, such as osteoporosis, cardiovascular diseases, and diabetes mellitus. In China, Korea, and Japan, herbs have been used for thousands of years to relieve perimenopausal symptoms. Angelicae sinensis, Panax ginseng, Flemingia macrophylla, Pueraria lobata, Trifolium pratense preparations, Vigna unguiculata, and Glycine max have special importance in TCM. Radix Angelicae sinensis (Dong Quai) is a commonly used Chinese herb that has traditionally been used to treat dysmenorrhoea and irregular menstruation and as a supportive herb for menopausal complaints; it has an estrogen-like effect on the vaginal mucosa.
Dong Quai (Angelica sinensis) has been used in traditional Chinese medicine as a "female ginseng" or tonifier, restoring many of the body's functions. It has been commonly used in combination with other herbal preparations for menopausal complaints.
Black cohosh (Cimicifuga racemosa), another plant with selective estrogen receptor modulator (SERM) properties, is an indigenous North American plant historically used by Native Americans for its analgesic effects to treat dysmenorrhea, labor pain, and arthralgias. In the 19th century, herbal physicians used the alcohol extract of the root to treat menstrual and menopausal complaints. Black cohosh is now widely used in Europe for menopausal complaints.
Phytoestrogen-rich plants have been used across various traditional medicine systems, such as Ayurveda, Traditional Chinese Medicine, and indigenous herbal practices, to address menopausal symptoms including metabolic imbalances and weight gain. Scientific interest in phytoestrogens grew after observing that women in some traditional cultures, such as Japan, experience fewer menopausal symptoms and lower incidences of breast cancer, heart disease, and osteoporosis compared to Western women. The average daily intake of isoflavones is around 45 mg in the East compared to just 2 mg in the West.
In documented ethnobotanical studies of traditional plant-based reproductive remedies, more than 60% of cases used fresh plant material to prepare remedies; over 70% of the remedies were applied orally, while the remaining ones were applied topically, and many remedies were prepared as mixtures of multiple ingredients.
Of the isoflavone class, the two most extensively studied are daidzein and genistein. These phytoestrogens are also the most biologically active and estrogenic phytochemicals. A great number of isoflavones have been identified in plants in the form of non-active glycosides (daidzin and genistin) and in the form of 4′-methylated derivatives (formononetin and biochanin A).
Bacterial daidzein conversion in the intestine yields S-equol, which has been shown to exhibit greater stability, absorbance, and a lower rate of clearance compared to its parent compound. This enantiomeric form has been linked with promising activity on sex-hormone receptors and modulatory effects related to the amelioration of various metabolic disorders including cancer, cardiovascular disease, and neurodegenerative conditions. Of all known isoflavones in nature and their metabolites, equol has been observed to have the highest affinity for estrogen receptors.
The three main groups of phytoestrogens — isoflavones, ellagitannins, and lignans — are transformed into equol, urolithins, and enterolignans, respectively, by bacteria. These metabolites have more estrogenic/antiestrogenic and antioxidant activities than their precursors, and they are more bioavailable.
The soy-derived genistein, coumestrol, and equol displayed a preference for transactivation of ERβ compared to ERα and were 10- to 100-fold less potent than diethylstilbestrol.
Phytoestrogens have a complicated mechanism of action involving an interaction with the nuclear estrogen receptor isoforms ERα and ERβ, with both estrogen agonist and estrogen antagonist effects. Depending on their concentration and bioavailability in various plant sources, phytoestrogens can act as estrogen agonists or antagonists. Phytoestrogens bind to nuclear ERs with a much lower affinity than endogenous estradiol and therefore are less potent in mediating genomic responses.
Many plants have been identified as containing phytoestrogens, some of which have also been classified as selective ER modulators (SERMs) because they have been shown to inhibit or stimulate estrogen-like actions in a cell-type, tissue-specific, and dose-dependent manner. The relative ratio of ERα and ERβ in a cell, as well as background estrogen levels, strongly influences the estrogenic potential of a phytoestrogen.
Phytoestrogens exert pleiotropic effects on cellular signaling. Due to activation or inhibition of the estrogen receptors ERα or ERβ, these compounds may induce or inhibit estrogen action and therefore have the potential to disrupt estrogen signaling. Most well-studied phytoestrogens — including genistein and daidzein — preferentially bind ERβ over ERα. In contrast, zearalenone (a mycoestrogen) was the most potent phytoestrogen-like compound tested and activated preferentially ERα.
Phytoestrogens potentially modulate signaling molecules via: (1) blocking the nuclear and membrane estrogen receptors (ER), (2) interfering with the growth factor receptor, (3) inhibiting the G protein-coupled receptor in ER-deficient cells, and (4) activating apoptosis and nullifying anti-apoptotic signals. They have multiple targets within cells, including the epigenome.
Knowledge of the relative ligand binding affinities of phytoestrogens, tissue distribution, and developmental pattern of expression of estrogen receptors may help to explain the tissue-specific actions of phytoestrogens. Tissue-specific expression of ERs, but also local regulation of estradiol levels, is crucial for the correct functioning of estrogen-responsive tissues.
Phytoestrogens, existing in plants as glycosidic conjugates, are partly absorbed through the gut barrier; however, most of the compounds are unabsorbed and undergo colonic metabolism. The colonic metabolites are shown to exhibit better bioavailability, more estrogenic/anti-estrogenic, and higher antioxidant activity than the parent compounds. These effects are observed with inter-individual variations, which have been attributed to the uniqueness of gut microbiota composition of each individual.
In vitro fermentation experiments have demonstrated that only the microbiota of a subset of subjects produced equol, while most showed production of O-desmethylangolensin (O-DMA) from daidzein. This equol-producer/non-producer dichotomy is a major source of inter-individual variability in clinical trial outcomes.
This is the most extensively studied clinical application for phytoestrogens, and the evidence base — though positive overall — remains heterogeneous.
A meta-analysis searched Medline, Cochrane, EMBASE, and Google Scholar databases until September 30, 2013, using the keywords vasomotor symptoms, menopausal symptoms, phytoestrogens, isoflavones, coumestrol, soy, and red clover. Inclusion criteria required randomized controlled trials (RCTs) in perimenopausal or postmenopausal women experiencing menopausal symptoms with oral phytoestrogen interventions. Outcome measures included Kupperman index changes, daily hot flush frequency, and likelihood of side-effects. Of 543 potentially relevant studies identified, 15 RCTs meeting inclusion criteria were included. The conclusion of this meta-analysis was that phytoestrogens appear to reduce the frequency of hot flushes in menopausal women, without serious side-effects.
An earlier systematic review reached a more skeptical conclusion: the available evidence suggests that phytoestrogens do not improve hot flushes or other menopausal symptoms, although they are well tolerated.
Clinical trials show that daidzein and genistein, especially in equol-producing individuals, can reduce vasomotor symptoms such as hot flashes and night sweats. While results across studies vary, consistent findings support their safety and modest efficacy, particularly for women unable or unwilling to use HRT.
Despite supplemental phytoestrogens being available and promoted to treat menopausal symptoms, there have been few randomized controlled trials of sufficient power and duration to reach conclusions regarding the impact on hot flashes and other menopausal symptoms as well as their long-term effects on the breast, uterus, brain, cardiovascular system, and thyroid function.
Overall evidence strength: Moderate and heterogeneous. Some positive RCT evidence exists, particularly for soy isoflavones and red clover extracts, but effect sizes are modest compared to hormone replacement therapy and are confounded by equol producer status, formulation type, and study duration.
A systematic review with meta-analysis of 18 RCTs found that daily intake of 106 mg (range 40–300 mg) of isoflavones for 6–24 months moderately but statistically significantly positively affected bone mineral density (BMD) compared with controls: lumbar spine weighted mean difference = 1.63 (95% CI: 0.51 to 2.75)%.
A multicenter, randomized, double-blind, placebo-controlled 24-month trial assessed the effects of daily supplementation with 80 or 120 mg of soy hypocotyl aglycone isoflavones plus calcium and vitamin D on bone changes in 403 postmenopausal women. The conclusion was that daily supplementation with 120 mg soy hypocotyl isoflavones reduces whole-body bone loss but does not slow bone loss at common fracture sites in healthy postmenopausal women.
A systematic review of 23 eligible studies included 3,494 participants enrolled in selected trials; most used a double-blind, placebo-controlled design. Different types of soy isoflavone extracts, including genistein extracts (alone or in combination with daidzein), dietary products containing different amounts of phytoestrogens, and red clover extracts were used. The duration of the interventions ranged from 7 weeks to 3 years. The conclusion was that isoflavones probably have beneficial effects on bone health in menopausal women; nevertheless, there were controversial reports about changes in BMD.
Phytoestrogens have been associated with improvements in bone health by promoting osteoblast activity and inhibiting osteoclast function, offering a potential preventive measure against post-menopausal osteoporosis.
For osteoporosis, tentative evidence suggests phytoestrogens may have similar effects in maintaining bone density to those of the related pharmaceutical compound ipriflavone.
Overall evidence strength: Moderate. Meta-analyses of RCTs show statistically significant but modest improvements in spinal BMD. Evidence for fracture risk reduction is lacking in human clinical trials. Results vary considerably by formulation, dose, and duration.
Epidemiologic data indicate that women ingesting high amounts of phytoestrogens, particularly as isoflavones in soy products, have less cardiovascular disease, breast and uterine cancer, and menopausal symptoms than those eating Western diets. Preclinical and clinical studies have found that isoflavones have lipid-lowering effects as well as the ability to inhibit low-density lipoprotein oxidation. They have also been shown to normalize vascular reactivity in estrogen-deprived primates.
Soya appears to have beneficial effects on blood lipids which may help to reduce the risk of cardiovascular disease and atherosclerosis. However, while RCTs document beneficial effects of phytoestrogens on surrogate parameters such as bone mineral density, vasodilation, platelet aggregation, insulin resistance, and serum concentrations of triglycerides, high-density lipoprotein, and low-density lipoprotein, none of the available RCTs documents a protective effect of phytoestrogens for the clinical end points of breast cancer, bone fracture, or cardiovascular events.
The therapeutic use of phytoestrogens for the treatment of cardiovascular diseases, which appears to be extremely promising, should be handled cautiously, considering the individual variances, dosage, and the specific components of phytoestrogens.
Overall evidence strength: Epidemiological associations are positive; effects on surrogate biomarkers (lipids, vascular reactivity) observed in RCTs. No definitive clinical endpoint evidence (myocardial infarction, stroke reduction) from RCTs. Requires further large-scale trials.
Determining whether phytoestrogens increase or reduce the risk of developing breast cancer has proven to be one of the most challenging human health impacts to address.
A total of 13 studies have assessed the direct relation between individual dietary intake of soy products and the risk of breast cancer. Overall, results do not show protective effects, with the exception perhaps for women who consume phytoestrogens at adolescence or at very high doses. Only four of these 13 studies are prospective, and none of them found statistically significant breast cancer reductions.
Twenty-two case-control and cohort studies examined the incidence of breast cancer among women with and without a diet high in phytoestrogens. A meta-analysis of 21 studies found a significantly reduced incidence of breast cancer among past phytoestrogen users. Importantly, prospective studies — which are more methodologically reliable — have not consistently confirmed this finding.
In conclusion, few prospective studies (n = 5) were done to assess the effects of phytoestrogens on breast cancer risk. None of them found protective effects. However, these prospective studies did not focus on "age at consumption," which seems to be important based on results from dietary case-control studies.
At dietary levels, phytoestrogen compounds are generally safe, although high-dose supplementation is discouraged in individuals with hormone-sensitive cancers. Emerging evidence suggests lifelong consumption of soy-based foods may reduce cancer risk.
Overall evidence strength: Weak and inconsistent. Epidemiological data are mixed; prospective human trials are few and do not demonstrate protective effects for breast cancer. Timing of exposure (especially adolescent consumption) may be an important but incompletely studied variable.
Certain plant compounds such as isoflavonoids, flavonoids, and lignans have been proposed as cancer-protective compounds in populations with low incidences of prostate diseases. In particular, soy contains the isoflavone genistein, a compound with many properties that could influence both endocrine and growth factor signaling pathways.
A meta-analysis included 11 studies (2 cohort and 9 case-control studies) on phytoestrogen intake and 8 studies on serum concentration. The pooled odds ratio showed a significant influence of the highest phytoestrogen consumption (OR 0.80, 95% CI 0.70–0.91) and serum concentration (OR 0.83, 95% CI 0.70–0.99) on the risk of prostate cancer. In stratified analysis, high genistein and daidzein intake and increased serum concentration of enterolactone were associated with a significant reduced risk of prostate cancer. However, no significant associations were observed for isoflavone intake overall, lignan intake, or serum concentrations of genistein, daidzein, or equol separately.
Phytoestrogens can cause growth arrest and in some cases apoptosis in prostate cancer cells in vivo and in vitro. This may be due to the estrogenic properties of the compounds or alternative mechanisms of action. A number of phytoestrogens have been shown to have anti-androgenic effects and antioxidant activities. Other mechanisms include inhibition of 5-alpha-reductase, 17-beta-hydroxysteroid dehydrogenase, aromatase, tyrosine-specific protein kinases, and DNA topoisomerase II.
Phytoestrogens (including isoflavones and flavonoids) have been examined in randomized controlled trials in humans on the primary, secondary, and tertiary prostate cancer prevention level. Despite the plethora of trials and the variety of examined interventions, the evidence supporting the efficacy of most dietary factors appears inadequate to recommend their use.
Overall evidence strength: Preliminary. Observational data suggest an association between genistein/daidzein intake and reduced prostate cancer risk. RCT evidence is insufficient to support clinical recommendations.
The therapeutic efficacy of phytoestrogens in the brain remains controversial. When administered singly, phytoestrogens appeared to be moderately neuroprotective. On the other hand, a clinical trial revealed that a soy protein supplement containing a mixture of phytoestrogens did not show improved cognitive function in postmenopausal women when treatment was initiated at age 60 years or older.
In vitro, in silico, and in vivo studies demonstrate the ability of daidzein and genistein to modulate estrogenic pathways, inhibit oxidative stress, and influence reproductive and neurological function.
Overall evidence strength: Weak. Preclinical data show promise; the one notable large clinical trial in older postmenopausal women was negative for cognitive outcomes. Age at initiation of supplementation may be a critical variable. Insufficient RCT evidence to support clinical use for cognitive protection.
Accumulating evidence from molecular and cellular biology experiments, animal studies, and, to a limited extent, human clinical trials suggests that phytoestrogens may potentially confer health benefits related to cardiovascular diseases, cancer, osteoporosis, and menopausal symptoms.
RCTs document beneficial effects of phytoestrogens on surrogate parameters including insulin resistance and platelet aggregation, suggesting potential areas for investigation in metabolic syndrome and diabetes, though definitive clinical evidence remains lacking.
Humans have estrogen receptors throughout the body that play a significant role in physiology; they are involved in reproduction, metabolism, digestion, mood, cognition, bone formation, cardiovascular health, and more. Consequently, phytoestrogen activity spans multiple organ systems:
Phytoestrogens are not accompanied by a universally standardized therapeutic dose. The following dosages reflect those used in published clinical research:
Phytoestrogens are administered commercially in multiple formats including: standardized tablet or capsule extracts; whole soy protein powders; functional food fortification; topical creams; and fermented soy food products (miso, tempeh, natto). Aglycone (unconjugated) forms are generally considered to offer greater bioavailability than glycoside (conjugated) forms.
A litany of health benefits — including a lowered risk of osteoporosis, heart disease, breast cancer, and menopausal symptoms — are frequently attributed to phytoestrogens, but many are also considered endocrine disruptors, indicating that they have the potential to cause adverse health effects as well. Whether phytoestrogens are beneficial or harmful to human health remains unresolved, and the answer is likely complex, depending on age, health status, and even the presence or absence of specific gut microflora.
Pharmacokinetic studies reveal moderate bioavailability and inter-individual variability due to gut microbiota metabolism. At dietary levels, phytoestrogen compounds are generally safe, although high-dose supplementation is discouraged in individuals with hormone-sensitive cancers.
As weak estrogen agonists/antagonists with molecular and cellular properties similar to synthetic endocrine disruptors such as Bisphenol A (BPA), phytoestrogens provide a useful model to investigate the biological impact of endocrine disruptors in general. Phytoestrogens belong to a class of compounds known as endocrine-disrupting compounds (EDCs), which are natural or synthetic compounds that interfere with the normal function of the endocrine system.
As a side effect of phytoestrogens as EDCs on postmenopausal women, an increased risk of endometrial hyperplasia and possible goitrogenic activity of the thyroid gland have been reported. The available literature suggests that phytoestrogens may contribute to toxicological effects on the female reproductive system. Naturally occurring EDCs have displayed significant toxicological effects on the uterus and endometrium, including morphological changes, cell proliferation, fibroids, and carcinogenesis.
Possible goitrogenic activity of the thyroid gland has been reported in association with phytoestrogen use in postmenopausal women. The concern relates primarily to soy isoflavones and their inhibitory effect on thyroid peroxidase. This effect may be particularly significant in individuals with pre-existing hypothyroidism or iodine deficiency. However, this area requires further investigation in adequately powered clinical trials.
Phytoestrogens, while generally thought to have relatively low binding affinity to ERs, are widely consumed and are components of infant formula. A recent study reported that urinary concentrations of the phytoestrogens genistein and daidzein were about 500-fold higher in infants fed soy formula compared with those fed cow's milk formula. Therefore, the potential for endocrine disruption by phytoestrogens in this population needs to be considered. Fetal exposure to phytoestrogens such as genistein or coumestrol in rodents disrupted specific hypothalamic-pituitary-gonadal axis functions and affected the expression of steroid hormone and other receptors.
Based on available evidence, phytoestrogens should only be used in selected populations, such as those presenting with mild to moderate vasomotor symptoms in early natural postmenopause. None of the compounds investigated have been proven to protect against breast cancer, bone fracture, or cardiovascular disease.
Health conditions that Phytoestrogens may help support.
Phytoestrogens are structurally diverse plant compounds (isoflavones, lignans, coumestans, stilbenes) that bind human estrogen receptors and modulate estrogenic activity. They are used as alternatives to hormone replacement therapy and have documented effects on menopausal symptoms, estrogen metabolism, and hormone-dependent tissue health in multiple clinical trials.
Phytoestrogens are a broad class of plant-derived compounds (isoflavones, lignans, coumestans) binding estrogen receptors, and are among the most studied non-hormonal approaches to menopausal hot flashes. Cochrane reviews and multiple systematic analyses confirm modest but statistically significant reductions in hot flash frequency versus placebo across multiple subclasses.
Phytoestrogens are plant-derived compounds (including isoflavones, lignans, and coumestans) that bind estrogen receptors and mimic weak estrogenic activity. Diets enriched with phytoestrogen-containing foods are repeatedly linked to reduced vasomotor symptom severity and bone integrity preservation in menopause. Multiple classes have been studied in RCTs.
Phytoestrogens are plant-derived compounds (isoflavones, lignans, coumestans) that bind estrogen receptors in bone tissue and exert bone-protective effects by reducing osteoclast activity and promoting osteoblast function. Multiple RCTs and meta-analyses support their role in attenuating postmenopausal bone loss, with the strongest evidence for isoflavones (genistein, daidzein) and lignans.
Phytoestrogens as a class—including isoflavones, lignans, and coumestans—modulate sex hormone signaling and SHBG levels relevant to PCOS. Multiple systematic reviews include phytoestrogenic compounds among evidence-based interventions for PCOS-related androgen excess and metabolic dysfunction.
Phytoestrogens are plant-derived compounds (isoflavones, lignans, coumestans, prenylated flavonoids) that bind ERβ as weak SERMs. They are the most extensively studied class of natural compounds for perimenopausal vasomotor symptoms, bone health, and mood. Major dietary sources include soy, red clover, flaxseed, and hops.
Phytoestrogens as a class—including soy isoflavones and red clover isoflavones—bind estrogen receptors and modulate the hormonal environment of PMS. They are listed among natural interventions studied for PMS management in systematic reviews and used in traditional and complementary medicine.
Body systems that Phytoestrogens may help support.
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