What Are Phytoestrogens?

These plant compounds can affect your hormones, the pros of which are debated

Tofu, soybeans, pomegranate, apple, tempeh, rice, and sesame seeds

Verywell / Anastasia Tretiak

Phytoestrogens are plant-based compounds that have similar effects to estrogen produced in the body. By binding to estrogen receptors, phytoestrogens can stimulate or suppress certain enzymes and hormones. They are believed to prevent or treat conditions associated with estrogen deficiency or imbalance, such as osteoporosis or menopausal hot flashes.

Practitioners of alternative medicine believe that phytoestrogens can help prevent heart disease and hormone-dependent cancers, including some forms of breast cancer. However, there is evidence that interfering with normal hormonal functions can have serious consequences.

Phytoestrogens are among the most controversial topics in the realm of nutrition and women's health today.

Also Known As

Phytoestrogen belongs to a group of substances known as phenolic compounds and is sometimes referred to as dietary estrogen. This is because it is derived from the breakdown of certain plant-based foods during digestion, including whole grains, seeds, beans, root vegetables, and soy. Phytoestrogen supplements are also available.

What Are Phytoestrogens Used For?

Phytoestrogens are not considered essential nutrients because their absence from a diet does not confer disease. They may, indeed, offer some positive health benefits; isoflavones, coumestans, and prenylflavonoids are three phytoestrogens with the strongest estrogenic effects. However, based on the current body of research, it is unclear whether such benefits outweigh the risks.

Much of the evidence supporting the use of phytoestrogen consumption is anecdotal. Although preliminary research does exist, conclusions are often limited by the small sample size and poor study design. There is simply too little evidence to confidently endorse phytoestrogens as a treatment for any health condition.

A review of some of the conflicting research on phytoestrogens highlights the reason behind the debate about their use.

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 LDL ("bad") cholesterol, as well as increases in HDL ("good") cholesterol compared to women given a placebo.

By contrast, a 2017 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 phytoestrogen 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. However, the findings regarding phytoestrogen supplements 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 (mg) per day increased bone mineral density in women by 54% while decreasing bone resorption (the breakdown of bone tissue) by 23%.

On the other hand, a 2015 study published in the journal Menopause reported that higher intake of isoflavones is associated with higher rates of bone mineral loss in the lumbar spine and neck in premenopausal women and those in early menopause.

Of the 1,927 women included in the study, Asian women had the highest risk of this, likely due to the fact that 99.5% had a high consumption of dietary soy. By contrast, Black and White women generally had a low intake of dietary isoflavones.

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 Medicines 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 they are 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.

Those with hormone-sensitive cancers should speak with their doctors about whether or not they can consume phytoestrogen supplements. In particular, studies have shown conflicting data regarding the effects of soy isoflavones taken with tamoxifen for breast cancer.

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 and Storage

If you're seeking to boost your phytoestrogen intake, you may be best served by using food sources, rather than supplements for a variety of reasons including ease, cost savings, and purity.

If you are considering supplementation, speak with your doctor about what product may suit your needs best and what dose is appropriate for you.

Food Sources

Foods especially rich in phytoestrogen include:

  • Seeds: flax, pumpkin, sunflower, poppy, and sesame
  • Whole grains: rye, oats, and barley
  • Bran: wheat, oat, and rye
  • Beans and lentils
  • Fruits: especially apples and berries
  • Soybeans and soy products: tempeh, soybeans, and tofu
  • Vegetables: especially cruciferous vegetables such as broccoli, cabbage, and Brussels sprouts

Ideally, opt for whole foods rather than highly processed products.

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. 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 better results.

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

Supplements certified organic by the U.S. Department of Agriculture 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.

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