Isoflavones are plant compounds found primarily in soybeans that mimic the action of the hormone estrogen. Foods rich in isoflavones have anti-inflammatory and antioxidant properties, which can help prevent cell damage.
Hormonal effects of isoflavones
Isoflavones are also known as phytoestrogens because they are plant-based (the word “phyto” means “from plants”) and have a similar structure to estrogen, which allows isoflavones to bind to estrogen receptors. Depending on a person’s hormonal status, isoflavones may affect a person in the same way that estrogen does by producing estrogenic or antiestrogenic effects. Studies involving isoflavone supplements for the treatment of menopausal symptoms have shown some benefits, such as:
Improved fatigue.
Improved irritability.
Reduced hot flashes.
Potential benefits of isoflavone consumption
Although research is limited, there are several conditions besides menopause that may be improved by isoflavones.
Breast cancer
In two separate reviews of several studies, researchers concluded that soy isoflavones may reduce the risk of breast cancer in premenopausal and postmenopausal women. In the past, there have been concerns that soy foods, due to their isoflavones, may increase the risk of breast cancer in women at risk and worsen the prognosis of breast cancer patients.
However, according to the researchers, clinical trials have consistently shown that isoflavone consumption does not negatively affect breast cancer risk markers. Studies involving more than 11,000 women from the United States and China suggest that eating soy after a breast cancer diagnosis significantly reduces the risk of recurrence and improves survival.
Current evidence suggests that soy foods are safe for women who have had breast cancer or are at risk of breast cancer. But it's still unclear whether soy isoflavone supplements are safe for these women.
Diabetes
Researchers who reviewed eight studies concluded that soy products, soy proteins, and soy isoflavones may be associated with a lower risk of type 2 diabetes, and that future studies should focus on the dose of soy isoflavones and soy proteins needed to reduce the risk of diabetes.
High cholesterol
Animal studies suggest that soy isoflavones lower total cholesterol and LDL cholesterol.
High blood pressure
Researchers who reviewed 68 published studies concluded that soy isoflavones have a beneficial effect on systolic blood pressure (the pressure when the heart pumps) during early menopause, but more research is needed to evaluate the effects of isoflavones on maintaining blood pressure and heart health.
Irritable bowel syndrome
One study suggested that combining isoflavones with vitamin D supplements in women with irritable bowel syndrome improved inflammation. Further studies are required to validate these findings.
Osteoporosis
A systematic review of the effects of isoflavones on bone mass concluded that isoflavone treatments provide a moderately beneficial effect against bone loss in postmenopausal women. Another study also concluded that soy isoflavones reduce bone mineral loss in the lumbar spine in postmenopausal women.
Other conditions
There is not enough evidence to support claims for its use in treating many medical conditions, including:
Alzheimer's disease.
Asthma.
Heart disease (such as stroke or heart attack).
Colic (in infants).
Crohn's disease.
Uterine cancer.
Stomach cancer.
Hepatitis C.
Premenstrual syndrome.
Enlarged prostate.
Prostate cancer.
Rheumatoid arthritis.
Thyroid cancer.
Kidney disease.
Potential side effects
Most side effects are associated with long-term use of supplements rather than food sources such as soy products.
It has not been proven whether plant-derived compounds, such as isoflavones, provide potential benefits that outweigh the risk factors.
Isoflavones have shown anti-inflammatory properties in animal studies, and the study authors also explain that safety has not been established, and there may be harmful side effects of isoflavones, such as reduced immune response and cancer-causing effects.
Some data suggest a link between long-term soy consumption and Kawasaki disease.
Another study found that exposure to soy-containing infant formula had negative effects on long-term growth in children.
There is not enough clinical research data to support the safe use of soy products during pregnancy or breastfeeding, especially at higher doses.
People with breast cancer should discuss the use of isoflavone supplements with their oncologist or healthcare provider because it is still uncertain whether they are safe in this situation.
Soy may affect thyroid function in people with iodine deficiency.
When taken for a short period of time (up to six months), soy is likely safe. Common side effects may include:
Gastrointestinal upset.
Constipation.
Diarrhea.
Allergic reactions.
Do isoflavones cause weight gain?
Research suggests that isoflavones found in soybeans do not generally cause weight gain. However, they may cause slight weight gain in young individuals, as well as people who are obese.
Drug interactions
Isoflavones may interact negatively with several medications, including:
Celecoxib.
Theophylline.
Paclitaxel.
Midazolam.
Imatinib.
Carbamazepine.
Valproic acid.
Repaglinide.
Omeprazole.
Monoamine oxidase inhibitors (MAOIs).
Warfarin.
Foods rich in isoflavones
The richest food sources of isoflavones include:
Soybeans, mature seeds, and green seeds (green soybeans).
Some products made from soybeans, including tofu, soy milk, miso, natto, and soy protein powder.
Lentils.
Dried peas.
Pinto beans.
Lima beans.
Additionally, small amounts can be found in the following foods:
Chickpeas.
Peanuts.
Pistachios.
Supplement Doses
Although isoflavones are most often consumed by eating foods that contain them, there are dietary supplements that contain them in capsule form that are taken orally. The following dosages of isoflavones are supported by clinical research studies:
For postmenopausal individuals: A supplement containing at least 54 mg of genistein (soy isoflavone) daily is suggested for the treatment of hot flashes.
For irritable bowel syndrome: A supplement containing 40 mg of isoflavones daily for 6 weeks.
For protection against osteoporosis: A dietary supplement with a dose of 80 mg of soy isoflavones daily has been associated with a reduced bone loss in postmenopausal individuals (protection against osteoporosis).
For general dietary supplements: There is no specific recommended dose for general use.
The safety of using dietary supplements cannot be guaranteed when taken for longer than six months.
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