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Table of Contents > Herbs & Supplements > Isoflavones Print

Isoflavones

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Also listed as: Soy isoflavones, Red clover isoflavones
Related terms
Background
Evidencetable
Tradition
Dosing
Safety
Interactions
Attribution
Bibliography

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, PromensilT, 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.

Background
  • 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.

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. GRADE *


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.

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.

B


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.

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.

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.

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.

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.

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.

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.

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.

C


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.

D
* Key to grades

A: Strong scientific evidence for this use
B: Good scientific evidence for this use
C: Unclear scientific evidence for this use
D: Fair scientific evidence for this use (it may not work)
F: Strong scientific evidence against this use (it likley does not work)


Tradition / Theory

The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.

  • Alcohol withdrawal, Alzheimer's disease, antioxidant, asthma, atherosclerosis (hardening of the arteries), burns, breast pain (mastalgia), bronchitis (inflammation of the airways), cognitive function, constipation, cough, diarrhea, endometrial cancer (cancer of the uterine lining), erectile dysfunction, exercise performance enhancement, eye disorders, gastrointestinal disorders, headache, heart disease, high cholesterol, high or low blood pressure, immune system regulation, indigestion, inflammation, kidney disease, lung cancer, memory, menstrual migraine, neurodegeneration (progressive deterioration of nerves), obesity, osteoporosis, prostate health, reproduction disorders, sexually transmitted disease, skin disorders, skin sores, stroke, thyroid disease (cancer), whooping cough.

Dosing

Adults (18 years and older)

  • Various sources suggest limiting the consumption of isolated isoflavones to no more than 50 milligrams daily.
  • For bone density, various doses of isoflavones have been taken by mouth daily for up to 12 months, including 80 milligrams of soy isoflavones, 54 milligrams of the isoflavone genistein, and one tablet of Promensil® red clover isoflavones containing 26 milligrams of biochanin A, 16 milligrams of formononetin, one milligram of genistein, and 0.5 milligrams of daidzein.
  • For lowering cardiovascular disease risk, two tablets of red cover isoflavones, each containing 25 milligrams of formononetin, 2.5 milligrams of biochanin, and less than one milligram of genistein and daidzein, have been taken by mouth once daily for four weeks. One to two tablets of Promensil® red clover isoflavones, each containing four milligrams of genistein, 3.5 milligrams of daidzein, 24.5 milligrams of biochanin, and eight milligrams of formononetin, have been taken by mouth daily for up to 10 weeks. Additionally, 80 milligrams of primarily formononetin or biochanin isoflavones have been taken by mouth for six weeks, and 30 milligrams each of daidzein and genistein isoflavones as part of Estromineral® have been taken daily by mouth for six months.
  • For diabetes, two tablets of red clover isoflavones, each containing 25 milligrams of formononetin, 2.5 milligrams of biochanin, and less than one milligram of genistein and daidzein, have been taken by mouth for four weeks.
  • For menopause, two tablets of Promensil® red clover isoflavones, each containing 40 milligrams of formononetin, daidzein, biochanin, and genistein, have been taken by mouth for 12 weeks. Two 325-milligram capsules of soy extract, containing a total of 17.5 milligrams of genistein, daidzein, biochanin, and formononetin isoflavones, have been taken by mouth twice daily for 16 weeks. Three hundred milligrams of soy extract, containing 120 milligrams of isoflavones (20% daidzein, 75% genistein, and 5% glycitein), has also been taken by mouth in two divided doses for six months. One hundred fourteen milligrams of isoflavones (58% glycitein, 36% daidzein, and 6% genistein) has been taken by mouth daily for three months. Thirty-five milligrams of high genistein-containing isoflavones from the product SoyaVital has been taken by mouth daily for 12 weeks. Additional studies have investigated 100 milligrams of isoflavones taken daily by mouth for four months, 54 milligrams of genistein taken daily by mouth for 12 months, and 40 milligrams of soy isoflavones taken by mouth for an unspecified amount of time. Specific dosing information from other studies demonstrating a lack of benefit was unavailable.
  • For improving mood and cognition in postmenopausal women, 60 milligrams of isoflavones has been taken by mouth daily for six months. One capsule of Solgen 40, containing 30 milligrams of isoflavones, has been taken by mouth twice daily for 12 weeks. Two tablets of the product Health Woman: Soy Menopause Supplement®, each containing 55 milligrams of isoflavones, have been taken daily by mouth for six months. Specific dosing information from other studies demonstrating a lack of benefit was unavailable.
  • For reducing body fat mass, two capsules of Fujiflavone P40T, containing a total of 38.3 milligrams of daidzin, 0.2 milligrams of malonyldaidzin, 2.1 milligrams of acetyldaidzin, 0.6 milligrams of daidzein, 8.6 milligrams of genistin, 0.6 milligrams of acetylgenistin, 0.2 milligrams of genistein, 23.4 milligrams of glycitin, and one milligram of glycitein, have been taken by mouth daily for 24 weeks. Specific dosing information from other studies demonstrating a lack of benefit was unavailable.
  • For vaginal dryness, three tablets, each containing 11 milligrams of glycitein, seven milligrams of daidzein, and one milligram of genistein, have been taken by mouth twice daily for three months.

Children (under 18 years old)

  • There is no proven safe or effective dose for isoflavones in children.

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

  • Avoid with known allergy or hypersensitivity to soy or soy-based products, or any part of an isoflavone product. Episodes of allergic reactions to soy have been reported. More information related to soy allergies may be found in the Soy monograph.

Side Effects and Warnings

  • Various sources suggest limiting the consumption of isolated isoflavones to no more than 50 milligrams daily.
  • Some side effects related to soy may also apply if isoflavones were involved.
  • Isoflavones may cause skin complaints, such as rashes, psoriasis, redness, and itching; gastrointestinal complaints, such as bloating, constipation, diarrhea, gas, nausea, loose stools, stomach cramps, abdominal pain, and loss of appetite; breast complaints, including early breast development, breast tenderness, or other breast changes; menstrual complaints, such as vaginal spotting, increased menstrual discomfort, and longer menstrual periods; worsening of hormone-sensitive conditions, such as endometriosis; pancreas damage (due to regular consumption of raw soybeans, soy flour, or protein powder made from raw, unroasted, or unfermented beans); immune effects; or changes in cognitive performance. Isoflavones may also increase the level of calcium in the blood, the incidence of blood clots and hot flushes, and the risk of developing kidney stones. Cases of thrush (fungal skin infection), goiter (enlarged thyroid gland), hypospadias (congenital birth defect of the urethra), muscle pain, swelling of the feet and ankles, migraine headaches, insomnia, and changes in white blood cell count have also been reported.
  • Use isolated soy and red clover isoflavones cautiously, due to their structural similarity to estrogens.
  • Isoflavones and red clover, which is a source of coumarin, may increase the risk of bleeding. Caution is advised in patients with bleeding disorders or in those taking drugs, herbs, or supplements that may increase the risk of bleeding. Dosing adjustments may be necessary.
  • Isoflavones may lower blood sugar and insulin levels. Caution is advised in patients with diabetes or hypoglycemia and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
  • Use cautiously in those taking hormonal products, due to the risk of changes in hormone levels.
  • Isoflavones may affect blood pressure. Caution is advised in patients taking drugs, herbs, or supplements that also affect blood pressure.
  • Because isoflavones contain estrogen-like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.
  • Use cautiously in those taking cholesterol- or lipid-lowering agents, as consumption of soy or isoflavones may lower cholesterol or lipid levels.
  • Use cautiously in patients with thyroid disorders or in those taking thyroid hormones, as soy and isoflavones may alter thyroid hormone levels or increase the risk of developing an underactive thyroid.
  • Avoid in patients with breast and other estrogen-related cancers, due to possible estrogen-like effects and a lack of available safety information.
  • Avoid use of higher-than-normal dietary amounts in children and pregnant or breastfeeding women, due to a lack of available safety information.
  • Avoid with known allergy or hypersensitivity to soy or soy-based products, or any part of an isoflavone product. Episodes of allergic reactions to soy have been reported.

Pregnancy and Breastfeeding

  • Use of higher-than-normal dietary amounts of soy or isoflavones is not recommended in children and pregnant or breastfeeding women, due to a lack of available safety information.
  • Theoretically, soy isoflavones may exert estrogen-like effects on developing fetuses and promote the development of female sex characteristics.
  • The use of soy infant formula has reportedly been associated with increased menstrual discomfort, longer menstrual periods, abnormal development and reproduction, accelerated puberty, and an increased risk of thyroid disorders. As well, the use of soy products during pregnancy may be associated with an increased incidence of hypospadias (a congenital birth defect of the urethra) in male births.

Interactions

Interactions with Drugs

  • Isoflavones may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants (blood thinners) such as warfarin (Coumadin®) or heparin, antiplatelet drugs such as clopidogrel (Plavix®), and nonsteroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).
  • Isoflavones may lower blood sugar and insulin levels. Caution is advised when using medications that may also lower blood sugar. Patients taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
  • Isoflavones may interfere with the way the body processes certain drugs using the liver's cytochrome P450 enzyme system. As a result, the levels of these drugs may be altered in the blood and may cause altered effects. Patients using any medications should check the package insert and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.
  • Isoflavones may affect blood pressure. Caution is advised in patients taking blood pressure-altering agents, due to the potential of isoflavones to have either additive or antagonistic effects with blood pressure-lowering agents.
  • Because isoflavones contain estrogen-like chemicals, possible interactions may occur when combined with other estrogenic agents.
  • Isoflavones may also interact with agents used for the heart, agents that affect the immune system, agents that affect blood vessel width, alzheimer's agents, antibiotics, anticancer agents, aromatase inhibitors, calcitriol, cholesterol- and lipid-lowering agents, cystic fibrosis transmembrane conductance regulator (CFTR) agents, diuretics (such as furosemide), gastrointestinal agents, hormonal agents (such as progesterone, luteinizing hormone, testosterone, and follicle-stimulating hormone), indomethacin, methotrexate, neurologic agents, osteoporosis agents, p-glycoprotein-regulated agents, selective estrogen receptor modifiers (SERMs, such as tamoxifen), thyroid hormones, tyrosine kinase inhibitors, and weight loss agents.

Interactions with Herbs and Dietary Supplements

  • Isoflavones my increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Gingko biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.
  • Isoflavones may lower blood sugar and insulin levels. Caution is advised when using herbs or supplements that may also lower blood sugar. Blood glucose levels may require monitoring, and doses may need adjustment.
  • Isoflavones may interfere with the way the body processes certain herbs or supplements using the liver's cytochrome P450 enzyme system. As a result, the levels of other herbs or supplements may be altered in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.
  • Isoflavones may affect blood pressure. Caution is advised in patients taking blood pressure-altering herbs or supplements, due to isoflavones potentially having either additive or antagonistic effects with blood pressure-lowering agents.
  • Because isoflavones contain estrogen-like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.
  • Isoflavones may also interact with various Alzheimer's herbs, antibacterials, anticancer agents, antioxidants, black cohosh (Actaea racemosa), calcium, carbohydrates, cholesterol- and lipid-lowering agents, dietary fiber, diuretics, fermented soy products, flaxseed, fructooligosaccharides, gastrointestinal herbs and supplements, ginseng (Panax ginseng), herbs and supplements used for the heart, herbs and supplements that affect the immune system, herbs and supplements that affect blood vessel width, hormonal herbs and supplements, iodine, magnesium, magnolia bark extract, neurologic herbs and supplements, osteoporosis herbs and supplements, p-glycoprotein-regulated herbs and supplements, phosphate, probiotics, protein, resveratrol, soy flour, thyroid agents, vitamin D, weight loss herbs and supplements, and wheat.

Attribution
  • This information is based on a systematic review of scientific literature edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography
  1. Adams KF, Lampe PD, Newton KM, et al. Soy protein containing isoflavones does not decrease colorectal epithelial cell proliferation in a randomized controlled trial. Am J Clin Nutr 2005;82(3):620-626.
  2. Atkinson C, Compston JE, Day NE, et al. The effects of phytoestrogen isoflavones on bone density in women: a double-blind, randomized, placebo-controlled trial. Am J Clin Nutr 2004;79(2):326-333.
  3. Atkinson C, Warren RM, Sala E, et al. Red-clover-derived isoflavones and mammographic breast density: a double-blind, randomized, placebo-controlled trial [ISRCTN42940165]. Breast Cancer Res 2004;6(3):R170-R179.
  4. Coon JT, Pittler MH, Ernst E. Trifolium pratense isoflavones in the treatment of menopausal hot flushes: a systematic review and meta-analysis. Phytomedicine 2007;14(2-3):153-159.
  5. Crisafulli A, Marini H, Bitto A, et al. Effects of genistein on hot flushes in early postmenopausal women: a randomized, double-blind EPT- and placebo-controlled study. Menopause 2004;11(4):400-404.
  6. Hidalgo LA, Chedraui PA, Morocho N, et al. The effect of red clover isoflavones on menopausal symptoms, lipids and vaginal cytology in menopausal women: a randomized, double-blind, placebo-controlled study. Gynecol Endocrinol 2005;21(5):257-264.
  7. Howes JB, Tran D, Brillante D, et al. Effects of dietary supplementation with isoflavones from red clover on ambulatory blood pressure and endothelial function in postmenopausal type 2 diabetes. Diabetes Obes Metab 2003;5(5):325-332.
  8. Lee YB, Lee HJ, Sohn HS. Soy isoflavones and cognitive function. J Nutr Biochem 2005;16(11):641-649.
  9. Lenn J, Uhl T, Mattacola C, et al. The effects of fish oil and isoflavones on delayed onset muscle soreness. Med Sci Sports Exerc 2002;34(10):1605-1613.
  10. Maskarinec G, Morimoto Y, Hebshi S, et al. Serum prostate-specific antigen but not testosterone levels decrease in a randomized soy intervention among men. Eur J Clin Nutr 2006;60(12):1423-1429.
  11. Messina M, Bennink M. Soyfoods, isoflavones and risk of colonic cancer: a review of the in vitro and in vivo data. Baillieres Clin Endocrinol Metab 1998;12(4):707-728.
  12. Messina M, Ho S, Alekel DL. Skeletal benefits of soy isoflavones: a review of the clinical trial and epidemiologic data. Curr Opin Clin Nutr Metab Care 2004;7(6):649-658.
  13. Teede HJ, Giannopoulos D, Dalais FS, et al. Randomised, controlled, cross-over trial of soy protein with isoflavones on blood pressure and arterial function in hypertensive subjects. J Am Coll Nutr 2006;25(6):533-540.
  14. Wu J, Oka J, Tabata I, et al. Effects of isoflavone and exercise on BMD and fat mass in postmenopausal Japanese women: a 1-year randomized placebo-controlled trial. J Bone Miner Res 2006;21(5):780-789.
  15. Zhuo XG, Melby MK, Watanabe S. Soy isoflavone intake lowers serum LDL cholesterol: a meta-analysis of 8 randomized controlled trials in humans. J Nutr 2004;134(9):2395-2400.

Copyright © 2011 Natural Standard (www.naturalstandard.com)


The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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