The word "phytoestrogen" is derived from phyto, meaning "plant" and estrogen, because of the ability of these compounds to affect estrogenic activity in the body. Phytoestrogens are a diverse group of polyphenolic, nonsteroidal plant compounds that may cause both estrogenic and antiestrogenic effects. The estrogenic effects of phytoestrogens are similar, although less intense, than those of estrogens made by the human body. There are reportedly approximately 300 plant species containing phytoestrogen compounds that have some degree of estrogen activity.
The three major classes of phytoestrogens are isoflavones, lignans, and coumestans. Isoflavones are prominent in soy-based foods. Lignans are minor components of cell walls and fibers of seeds, fruits, berries, vegetables, grains, and nuts. Linseed (flaxseed) is a rich source of lignans. The primary coumestan is coumestrol. It is found in alfalfa and clovers, and in low levels in soybeans and peas.
Several population studies have indicated that phytoestrogens have health benefits. These include possible protection against menopausal symptoms and osteoporosis, as well as a potential reduction in breast cancer, prostate cancer, and cardiovascular disease risks. Both isoflavone and lignan phytoestrogens may have antioxidant activity.

Related Terms

8-Prenylnaringenin (8-PN), biochanin A, coumestans, coumestrol, daidzein, enterodiol, enterolactone, equol, flax phytoestrogens, flaxseed, formononetin, genistein, glycitein, hop extract, Humulus lupulus L., isoflavones, isoflavonoid phytoestrogen, lignans, matairesinol, O-desmethylangolensin (O-DMA), prenylflavonoids, Pueraria lobata (kudzu), red clover, secoisolariciresinol diglucoside (SDG), soy.
Combination product examples: MenoHop®, PHYTO SOYA®, Promensil®, Rimostil®, SoyaVital®.
Note: This review does not include mycoestrogens, which are estrogenic fungal products and not intrinsic components of plants. They are found in pasture grasses and legumes infected by the fungal genus Fusarium.

evidence table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Cardiovascular risk reduction (postmenopausal) (Grade: B)
Evidence suggests that certain populations that consume large amounts of soy protein have lower cardiovascular morbidity and mortality. Soy protein has been reported to reduce serum lipid levels by up to 10%. Preliminary evidence suggests that soy protein is superior to isoflavones isolated from red clover for reduction of serum lipid levels. Additional research is needed in this area.
Menopausal symptoms (Grade: B)
Foods rich in phytoestrogens may help alleviate symptoms of menopause, such as vaginal dryness, burning, itching, painful intercourse, and decreased interest in sex. Additional, well-designed studies are needed before firm conclusions may be made.
Osteoporosis prevention (Grade: B)
It has been theorized that phytoestrogens, such as isoflavonoids found in soy and red clover, may increase bone mineral density in postmenopausal women and reduce the risk of fractures. Further studies are required before a firm conclusion may be made.
Cognitive function (Grade: C)
Some evidence suggests that isoflavones may have a beneficial effect on cognitive function in postmenopausal women. Additional research is needed in this area.
Growth (bones) (Grade: C)
Multiple studies have shown that dietary intake of phytoestrogens derived from soy, lignans, or red clover reduces the risk of osteoporosis in postmenopausal women by inhibiting bone resorption, stimulating bone formation, preventing bone loss, and increasing bone mineral content. Additional studies are needed before a conclusion can be made.
Migraine (menstrual) (Grade: C)
Approximately 30% of women afflicted with migraine have headaches associated with menstruation. Preliminary research suggests that a combination product containing soy, dong quai, and black cohosh may be effective in preventing menstrual migraines. Further research with phytoestrogens alone is needed.
Prostate cancer (Grade: C)
In laboratory research, phytoestrogens had anticarcinogenic properties, such as growth arrest, and may have caused programmed cell death in prostate cancer cells. Additional research is needed in this area.