The Health Benefits of Isoflavones (2024)

Isoflavones are plant-based compounds primarily found in soybeans that mimic the action of the hormone estrogen. Foods rich in isoflavones possess anti-inflammatory and antioxidant properties, which can help prevent cell damage. Some studies suggest that isoflavone supplements may alleviate menopause symptoms and prevent osteoporosis in postmenopausal people.

Additionally, there is some evidence that isoflavone supplements could aid in preventing heart disease and certain cancers. However, more research is needed to confirm their effectiveness.

Hormone Effects of Isoflavones

Isoflavones are also known as phytoestrogens. That's because they are plant-based ("phyto" means "from plants") and they have a similar structure to estrogen. This allowsisoflavonesto bind with estrogen receptors.

Depending on the hormone status of a person,isoflavonesmay affect a person in the same way that estrogen doesbyproducing either estrogenic or antiestrogenic effects.

Instudiesinvolvingisoflavonesupplements for menopausal symptoms, some benefits have been shown, such as:

• Improving fatigue
• Improving irritability
• Decreasing hot flashes

Researchers reviewed 68 publications related to isoflavone consumption and menopausal symptoms and health conditions. They concluded consuming isoflavones reduces hot flashes even accounting for the placebo effect. However, more research is needed using standardized protocols (such as the same type and dosage of isoflavones and study duration) to confirm health effects.

Another review of 60 studies found that some plant-based therapies—such asisoflavones—worked to provide a modest reduction in hot flashes and vaginal dryness, but weren't effective for reducing night sweats.

Some case reports indicate that isoflavones in red cloverhelpreduce hot flashes and anxiety during menopause.Although the herb is marketed as a dietary supplement called Promensil, studies on the effects of red clover on menopause symptoms such as hot flashes have had inconsistent results.

Potential Uses for Isoflavones

In Asia, where soy is a staple in the diet, the rate of heart disease, breast cancer, and prostate cancer is lower than in the U.S.

Although the research is limited, there are several conditions in addition to menopause that may improve with the use ofisoflavones.

Breast Cancer

In two separate reviews of numerous studies, researchers concluded that consuming soy isoflavones can reduce the risk of breast cancer in pre-menopausal and post-menopausal women.

In the past, there have been concerns that soy foods, because they contain isoflavones, may increase the likelihood of breast cancer in high-risk women and worsen the prognosis of breast cancer patients.

However, according to researchers, clinical trials consistently show that consuming isoflavones does not adversely affect markers of breast cancer risk. And studies involving over 11,000 women from the U.S. and China show that soy intake after a breast cancer diagnosis significantly reduces recurrence and improves survival.

Current evidence indicates that it’s safe for women who have had breast cancer or who are at risk for breast cancer to eat soy foods. What is still uncertain is whether soy isoflavone supplements are safe for these women.

Diabetes

Researchers who reviewed eight studies concluded soy products, soy protein, and soy isoflavones might be associated with a lower risk of type 2 diabetes and that future studies should focus on what dose of isoflavones and soy protein is needed to lower diabetes risk.

Evidence also suggests that fermented soy products may be better for preventing or delaying the progression of type 2 diabetes compared with nonfermented soybeans, but more human studies are needed to make definitive conclusions.

High Cholesterol

Studies, of both animals and humans, strongly suggest that isoflavones from soy reduce both total cholesterol and LDL cholesterol. It appears from these studies that only protein-based food sources ofisoflavonessuch as tofu or tempeh were found to lower cholesterol; isoflavonesupplements were not effective.

Red clover has also been found to have a cardiovascular benefit, lowering total cholesterol in peri- and post-menopausal women.

High Blood Pressure

Researchers who reviewed 68 publications concluded that soy isoflavones have a beneficial effect on systolic blood pressure (the pressure when the heart pumps) during early menopause.

Another study including 99 women found that consuming isoflavones reduced diastolic blood pressure (the pressure when the heart is at rest). The study authors noted that more research is needed to assess the effects of isoflavones on maintaining blood pressure and heart health.

Irritable Bowel Syndrome (IBS)

One study suggested that a combination of soy isoflavones and vitamin D supplementation in women with irritable bowel syndrome (IBS) improved inflammation and intestinal permeability. However, more research is needed to confirm these findings.

Osteoporosis

Almost 20% of women over 50 in the U.S. have osteoporosis (brittle, fragile bones).

A systematic review of the effects of isoflavones on bone mass concluded that isoflavone treatments offer a moderately beneficial effect against bone loss in menopausal women. Another review also concluded that soy isoflavones reduce lumbar spine bone mineral loss in menopausal women.

Other Conditions

There is NOT enough evidence to back the claims of usingisoflavonesto treat many medical conditions, including:

• Alzheimer's disease
• Asthma
• Heartdisease (such as stroke or heart attack)
• Colic(in infants)
• Crohn's disease
• Endometrialcancer (cancer of the lining of the uterus)
• Stomachcancer
• HepatitisC
• Premenstrualsyndrome (PMS)
• Enlargedprostate
• Prostatecancer
• Rheumatoidarthritis
• Thyroidcancer
• Kidneydisease

Possible Side Effects of Isoflavones

Most of the side effects of isoflavones are associated with long-term use of supplements and not from dietary sources such as soy products.

• A 2016 review published in theBritish Journal of Pharmacology, reports that it has not been well-established whether plant-derived compounds, like isoflavones, provide potential benefits that outweigh the risk factors.
• A study published in the journal Nutrients reports that, "...isoflavones exhibit impressive anti-inflammatory properties in various animal models, and even in humans, through increased antioxidative activities." The study authors also explain that safety hasn't been established and there may be harmful side effects of isoflavones, like potentially lowering the immune response and causing cancer.
• Some data shows that there is a link between long-term soy consumption and Kawasaki disease (KD). Soy isoflavones play a role in this.
• Anotherstudydiscovered that exposure to soy-based infant formula resulted in negative effects on the long-term development of infants.
• Animalstudieshave shown that the isoflavone genistein may have adverse effects on the developing reproductive system of assigned females.

Short-Term Use

When ingested on a short-term basis (up to six months in duration), soy is considered possibly safe. Common side effects may include:

• GI upset
• Constipation
• Diarrhea
  
• Allergicreactions
  

Precautions and Contraindications

There are precautions associated with soy products and isoflavones:

• There is not enough clinical research data to support the safe use of soy products when pregnant or breastfeeding, particularly at higher doses.
• Those with breast cancer should discuss the use of isoflavone supplements with their oncologist orhealthcareprovider since it is still uncertain whether they are safe in this situration.
• Soy may alter thyroid function in people with iodine deficiency.

Drug Interactions

Isoflavonesmay adversely interact with numerous medications, including:

• Celecoxib
• Theophylline
• Paclitaxel
• Midazolam
• Imatinib
• Carbamazepine
• Valproic acid
• Repaglinide
• Omeprazole
• Monoamine oxidase inhibitors (MAOIs)
• Warfarin

Anyone taking prescription or over-the-counter medications should talk with their healthcare provider before takingisoflavonesor any other herbal or nutritional supplement.

Foods High in Isoflavones

The richest food sources of isoflavones include:

• Soybeans, both mature seeds and green (edamame)
• Some products made from soybeans, including tofu, soymilk, miso, natto, and soy protein powder
• Lentils
• Split peas
• Pinto beans
• Lima beans
  

Isoflavones are also found in small amounts in the following foods:

• Chickpeas
• Fava beans
• Pistachios
• Peanuts

Sources and Composition

While soybeans have the highest level of isoflavones, herbal sources like red clover (Trifolium pratense) and alfalfa (Medicago sativa) are also rich in isoflavones. Like soy, red clover is considered a legume that containsphytoestrogens.

In their most common form, soy isoflavones include:

• Genistein
• Daidzein
• Glycetein

Isoflavonesfound in red clover include:

• Formononetin
• Biochanin A
• Daidzein
• Genistein

Supplement Dosages

Although isoflavones are mostly consumed by eating foods that contain them, there are isoflavone supplements in capsule form that are taken by mouth.

The following doses of isoflavones are backed by clinical research studies:

• For postmenopausal individuals: A supplement with at least 54 mg of genistein (a soy isoflavone) per day is suggested for hot flashes.
• For IBS: Take a supplement of 40 mg of isoflavones per day for six weeks.
• For protection against osteoporosis: A supplement of 80 mg per day of soy isoflavones was associated with a dosage that reduced bone loss in postmenopausal individuals (protecting against osteoporosis).
• For general supplementation: There is no recommended dose established for general use.

The safety of the use ofisoflavones supplements cannot be guaranteed when taken for a duration of longer than six months.

What to LookFor

Since supplements are not regulated by the FDA, there are several things to look for to ensure quality and effectiveness inisoflavonesand other natural supplements.

• Look for a product that is made into an extract and avoid powder supplements which may be much weaker in strength (but cheaper to make).
• Ensure that the strength and dosage of theisoflavonesupplement align with recommendations from clinical research data.Those who are unsure should consult with their healthcare professional or pharmacist.
• Check the label to make sure that the product has active ingredients, such as naturalphytoestrogenscontained inisoflavones(in the extract form).
• Check to ensure that the product is quality-tested for safety and strength by a third party and made in the USA.
• Choose non-genetically modified isoflavones products.
• Choose a company that backs its products with a 60-day guarantee to allow enough time to evaluate the effectiveness of the product.

Summary

Although much of the clinical research data onisoflavonessupports its health benefits, such as promoting cardiac health, reducing menopausal symptoms and more, there is quite a bit of contradictory information.

Because of the number of mixed study data reports onisoflavones, it's strongly suggested you consult with your healthcare provider before using this nutritional supplement in any form. This includes eating large amounts of soy products, ingesting herbal sources of isoflavones from red clover, or taking any supplements with any other form ofisoflavones.