The Health Benefits of Phytoestrogens

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Phytoestrogens are plant-based compounds that have similar effects to estrogen produced in the body. Often referred to as "dietary estrogen," these compounds are believed to prevent or treat conditions associated with estrogen deficiency, such as osteoporosis or menopausal hot flashes.

Phytoestrogens are found in high concentrations in certain plant-based foods, including whole grains, seeds, beans, root vegetables, and soy. They belong to a group of substances known phenolic compounds that are derived from the breakdown of these plants during digestion. Isoflavones, coumestans, and prenylflavonoids are three phenolic compounds with the strongest estrogenic effects.

By binding to estrogen receptors in the body, phytoestrogens can either stimulate or suppress certain enzymes and hormones in a way that benefits health. Practitioners of alternative medicine believe that doing can help prevent heart disease and hormone-dependent cancers (including some forms of breast cancer).

Despite such claims, there is evidence that interfering with normal hormonal functions can have serious consequences. In fact, phytoestrogens are among the most controversial topics in the realm of nutrition and women's health today.

Health Benefits

Much of the evidence supporting the health benefits of phytoestrogen is anecdotal. Although preliminary research does exist, their conclusions are often limited by the small size or poor design of the study. This is not to suggest that phytoestrogens are without benefits. For the most part, however, there is simply too little evidence to endorse phytoestrogens as a treatment for any health condition.

Based on the current body of research, it is unclear whether the benefits of phytoestrogens outweigh the risks.

High Cholesterol

Several studies have suggested that phytoestrogens may prevent heart disease by reducing cholesterol levels and the risk of atherosclerosis ("hardening of the arteries").

A 2012 study in the German medical journal Geburtshilfe und Frauenheilkunde reported that postmenopausal women given a daily isoflavone extract (derived from either soybeans or red clover) experienced significant decreases in total cholesterol, triglycerides, and "bad" LDL cholesterol as well as increases in "good" HDL cholesterol compared to women given a placebo.

By contrast, a 2016 review of studies in the British Journal of Pharmacology concluded that isoflavones do not significantly alter lipid levels or reduce cardiovascular risk in anyone other than heavy smokers.

Bone Loss

Some postmenopausal women use phytoestrogens supplements as an alternative to hormone replacement therapy (HRT). It is believed that doing so can mitigate the symptoms of menopause and decrease the rate of osteopenia (bone loss) that occurs as a consequence of menopause. The findings to date have been mixed.

A 2012 review of studies in the Asian Pacific Journal of Tropical Medicine concluded that soy isoflavone supplements taken in doses greater than 75 milligrams per day increased bone mineral density in women by 54% while decreasing bone resorption (the breakdown of bone tissue) by 23%.

By contrast, a 2015 study published in the journal Menopause reported that higher intakes of isoflavones were associated with higher rates of bone mineral loss in the lumbar spine and neck in premenopausal women.

Cancer

The use of phytoestrogens in the prevention of cancer remains highly controversial. Some studies have suggested a protective benefit, while others warn of potential harms.

Among the positive findings, a 2016 review of studies in Science Reports found that increased soy isoflavone consumption corresponded to a 23% reduction in the risk of colorectal cancer. (Despite the positive findings, the researchers conceded that other factors could account for the effect given the variations and inconsistencies in the reviewed studies.)

Other reviews have suggested that soy isoflavones offer protection against endometrial cancer and gastrointestinal cancers.  However, the reviews mostly focused on soy intake rather than the use of controlled soy isoflavone supplements.

As for breast cancer, phytoestrogens may have positive or detrimental effects depending on which study you refer to. A comprehensive review published in Medicine in 2017 examined both sides of the issue and found that soy isoflavones, while able to induce apoptosis (cell death) in test-tube studies, were just as likely to stimulate breast cancer growth in animal studies.

Despite the contradictory findings, the investigators highlighted several trials in which the high consumption of soy (mainly among Asian women) corresponded to decreases in cancer mortality and breast cancer recurrence. Further research is needed.

Possible Side Effects

Generally speaking, phytoestrogens in plant-based foods are safe to consume if used as part of a balanced diet. By contrast, little is known about the long-term safety of phytoestrogen supplements.

Soy isoflavones, the type most commonly used in phytoestrogen supplements, may cause stomach upset, bloating, gas, and nausea. Allergic reactions are rare but may incur in people with a known soy allergy.

Due to their estrogen-like effect, phytoestrogen supplements should be avoided in women with estrogen-receptor-positive breast cancer or people with other hormone-sensitive cancers, including endometrial, ovarian, and prostate cancer.

Phytoestrogen supplements should not be used with tamoxifen. By binding to the same estrogen receptors used by tamoxifen, phytoestrogens can "compete" with the drug and reduce its efficacy. Doing so may increase the risk of breast cancer recurrence.

The safety of phytoestrogen supplements in pregnancy is unknown. To be safe, avoid taking any supplemental form of phytoestrogen if you are pregnant or breastfeeding.

Selection, Preparation, and Storage

Phytoestrogen can be obtained from dietary supplements and certain plant-based foods. Despite their potential benefits, they are not considered essential nutrients because their absence from a diet does not confer to disease.

Dietary Supplements

Phytoestrogen supplements are typically sold in capsule or tablet form and can be purchased online or at stores specializing in dietary supplements. While a great many of these products contain soy isoflavones as their central ingredient, others are made with phytoestrogen-rich flaxseed oil or red clover isoflavones.

Always read the product label to determine which type of phytoestrogen is used (e.g., soy isoflavone, flaxseed oil) as well as the quantity measured in milligrams (mg). While there are no guidelines for the appropriate use of phytoestrogen supplements, studies have used soy isoflavones in doses of up to 100 mg for 12 months with no notable side effects. There is no evidence that higher doses confer to better results.

To ensure quality and safety, only buy supplements that have been tested by an independent certifying body like the U.S. Pharmacopeia (USP), ConsumerLab, or NSF International.

Supplements certified organic by the U.S. Department of Agriculture (USDA) can further ensure that you are not exposed to pesticides or other unwanted chemicals.

Phytoestrogen supplements, including soy isoflavones, can be stored safely in a cool, dry room. Never use a supplement past its expiration date.

Food Sources

If wanting to boost your phytoestrogen intake, you may be better served to do so with food rather than supplements. Among the plants especially rich in phytoestrogen are:

  • Alfalfa
  • Anise
  • Apples
  • Barley
  • Beans
  • Beer
  • Bourbon whiskey
  • Carrots
  • Coffee
  • Fennel
  • Ginseng
  • Hops
  • Lentils
  • Licorice
  • Linseed (flaxseed)
  • Mint
  • Mung beans
  • Oats
  • Pomegranate
  • Red clover
  • Rice
  • Rice bran
  • Sesame seeds
  • Soybeans
  • Tempeh
  • Tofu
  • Wheat berries
  • Wheat germ
  • Yams
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Article Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Zhang GQ, Chen JL, Liu Q, et al. Soy Intake Is Associated With Lower Endometrial Cancer Risk: A Systematic Review and Meta-Analysis of Observational StudiesMedicine (Baltimore). 2015 Dec;94(50):e2281. doi:10.1097/MD.0000000000002281.


  2. Tse G, Eslick D. Soy and isoflavone consumption and risk of gastrointestinal cancer: a systematic review and meta-analysisEur J Nutr. 2016 Feb;55(1):63-73. doi: 10.1007/s00394-014-0824-7


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