Isoflavones were first discovered due to their ability to disrupt the action of estrogen in animals. As a result, they are classified as a type of phytoestrogen, which, as the name suggests, is a naturally occurring plant ("phyto") chemical with estrogen-like properties.
In the diet, isoflavones may be found in soybeans; soy-based foods, including soy milk, flour, nuts, tempeh, and tofu; and legumes, such as peas, peanuts, chick peas, and navy beans. Although in the traditional Asian soybean, Glycine soja, isoflavone levels are typically very low, levels are much higher in the Glycine max bean variety due to its mass production over the past 60 years and its increased need for protection from pests. Apart from food sources, isoflavones may also be purchased in purified form, often isolated and extracted from soy or red clover. In supplements, soy isoflavones are normally found as isoflavone glycosides (genistin, daidzin, glycitin).
Unlike in Western cultures, where the intake of soy-based foods is typically low, dietary intake of isoflavones is generally higher in certain Asian populations, where soy-based foods are more commonly eaten. Over the past decade, however, Western soy consumption has increased due to the growing popularity of soy-based foods and the increased attention to their proposed health benefits. Currently, infant soy formulas account for more than 25% of all infant formulas sold. As of 1999, the U.S. Food and Drug Administration (FDA) permits soy protein products (a source of isoflavones) to display a health claim for a reduced risk of heart disease.
Therapeutically, isoflavones are commonly used in the West to reduce menopausal symptoms such as hot flashes, to lower cardiovascular disease risk factors, and to prevent osteoporosis. Isoflavones have also been implicated for the treatment of high cholesterol, diabetes, vaginal dryness, various types of cancer, and postmenopausal mood and cognition. However, results generally differ between studies, and firm conclusions are difficult to make. Additional research in these areas is needed.

Related Terms

Acetyldaidzin, acetylgenistin, acetylglycitin, Actaea racemosa, aglycones, alfalfa, biochanin, biochanin A, biochanin-enriched isoflavone, black cohosh, chick pea, Cimicifuga racemosa extract BNO 1055, daidzein, daidzein glycosides, daidzin, daizuga-cha, dehydroequol, edamame, equol, Fabaceae (family), fava bean, fermented soy foods, flavanol, flavonoids, formononetin, frijol de soya, fujiflavone P10, genestein, genistein, genistein glycosides, genistin, glabridin, glabrin, glabrol, glabrone, Glycine max, Glycine soja, glycitein, glycitein glycosides, glycitin, glycyrol, glyzarin, haba soya, hydrolyzed soy protein, ipriflavone, isoflavone aglycones, ISP56, ISP90, kinako, kudzu, kumatakenin, Kuromame-cha, Kuromame-cha Gold, Kuromame-soymilk drink, legume, Leguminosae (family), licoflavonol, licoisoflavanone, licoisoflavone A, licoisoflavone B, licoricone, liquiritin, lupine, Lupinus spp., malonyldaidzin, malonylgenistin, malonylglycitin, miso, natto, osja, peanut, phaseollinisoflavan, phyto soy, phytoestrogens, plant estrogen, polyphenols, Promensil™, psoralea, Psoralea corylifolia, PTI G-2535, PTI G-4660, Pueraria lobata, red clover, red clover extract (MF11RCE), Rimosti®, shoyu, sojabohne, soy desserts, soy drinks, soy fiber, soy food, soy germ, soy isoflavones, soy milk, soy protein, soy protein extract, soya, soya bean, soya isoflavones, SoyaVital, soybean, soybean curd, soybean phytoestrogens, soyfood, soymilk, soy-protein, tempe, tempeh, texturized vegetable protein, tofu, Trifolium pratense, Trifolium pratense isoflavones, Vicia faba.
Select combination products: Abaco (isoflavones, soy fiber, soy phospholipids); Abalon® (soy protein, cotyledon fiber, isoflavones); Daizuga-cha (drink containing isoflavones); Isosoy® (soy germ containing 60mg of isoflavones, 56mg of lipids, 202mg of protein, 141mg of carbohydrates, and 19mg of fiber); Soyselect® (soy extract containing isoflavones and saponins).
Note: This summary refers only to isolated isoflavones. As such, ipriflavones, soy protein, and sources of isoflavones, such as kudzu, licorice, and red clover, are not included unless the isoflavones were specifically isolated for investigation. However, in order to provide a more complete safety assessment, relevant safety information from studies involving the effects of isoflavones as part of soy protein is included.

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.
Bone density (Grade: B)
Preliminary evidence suggests that isoflavones may contribute to bone health by preventing bone loss, promoting bone formation, and increasing bone density. Due to conflicting study results, additional research in this area is needed.
Mood and cognition in post-menopausal women (Grade: B)
Limited evidence suggests that isoflavones may improve both mood and memory in postmenopausal women. However, due to a lack of available research and varying study results, firm conclusions in this area cannot be made. Additional high-quality research is needed.
Breast cancer (Grade: C)
Preliminary findings on the effects of soy isoflavones on breast cancer risk and breast tissue density are inconsistent and inconclusive. Research on the long-term, preventive, and isolated effects of isoflavones on breast cancer is currently lacking and warrants further investigation. Until such research becomes available, purified isoflavones should be avoided in individuals diagnosed with breast cancer, or in those with a high risk of developing breast cancer.
Cardiovascular disease risk (Grade: C)
Preliminary evidence suggests that isoflavones, as a component part of soy protein isolate, reduces LDL cholesterol. In contrast, purified soy isoflavones are suggested as having little effect on LDL cholesterol levels. Additional research in this area is needed to clarify the existing controversy in study results.
Colorectal cancer (Grade: C)
Preliminary findings on the effects of isoflavones on colorectal cancer risk are inconsistent and inconclusive. Results vary between studies and suggest a need for additional research in this area.
Diabetes (Grade: C)
Very few high-quality studies have investigated the effects of isoflavones on blood sugar levels. Due to the current lack of available research in this area, conclusions are limited. Further investigation is needed.
Menopause (Grade: C)
Preliminary research suggests that isoflavones may reduce hot flashes in postmenopausal women. However, results are inconsistent as to whether this effect is limited to the activity of isoflavones alone, or as a component of soy protein. Additional research in this area is needed.
Muscle soreness (Grade: C)
Preliminary research suggests that isoflavones do not prevent delayed-onset muscle soreness. However, the quality of available research in this area is limited. Further research is needed before conclusions may be made.
Prostate cancer (Grade: C)
Preliminary research suggests that isoflavones may be associated with lower prostate-specific antigen (PSA) levels in prostate cancer patients, and a reduced risk of prostate disease. Though results appear favorable, they are limited by a lack of statistical significance and strict study design. Additional well-designed clinical studies are required before any conclusions may be drawn.
Reducing body fat mass (Grade: C)
Preliminary research on the effect of purified isoflavones on body fat and body weight is currently unclear. While some studies suggest that isoflavones decrease body fat mass, others suggest that they have no effect on fat mass or body weight. Further research in this area is needed.
Vaginal dryness (postmenopausal women) (Grade: D)
There is a lack of available research investigating the effect of isoflavones on vaginal dryness. Although one well-designed study suggests that soy isoflavones do not improve symptoms of dryness, further research in this area is needed before any conclusions may be made.