Soy Isoflavones Supplements: Benefits, Side Effects & Dosage

What are Soy Isoflavones?

Soy isoflavones (ISF) are nutritional supplements derived from soy. Many Asian cultures have been consuming soy foods for centuries. Research suggests that soy isoflavones help lower the risk for heart disease, diabetes and atherosclerosis. In addition, soy helps minimize menopause symptoms (x).

Research indicates that soy isoflavones may help minimize or eliminate the risk factors associated with cardiac disorders, including high liver and blood triglycerides and low HDL cholesterol and an imbalanced HDL/LDL ratio. In addition, soy proteins play essential roles in regulating lipid metabolism (x).

Benefits of Soy Isoflavones

Substitute for Meat Protein

Soy isoflavones contain all the essential amino acids the body requires for healthy growth (x). The high-quality isoflavones derived from soy are comparable to animal-sourced proteins, but they have significantly less fat and cholesterol. Soy foods contain about 4 mg of ISF per gram. On the other hand, soy ISF supplements contain about 500 mg of ISF per gram (x).

Soy ISF may be an excellent substitute for meat protein because they offer complete protein profiles. Animal meats usually have complete protein profiles, but they often contain high quantities of saturated fats (x).

Energy Booster

Like tofu and soy milk, soy ISF is rich in amino acids that the body usually converts into energy (x). In addition, soy ISF has plenty of other nutrients, including vitamin D, which plays a vital role in healthy bone and tissue development (x).

Improves Cognitive Function

The natural aging process affects mood and cognitive function (x). For example, as women reach menopause, estrogen levels drop and research associates low estrogen levels in women with diminishing cognitive functions, including memory and learning. Soy ISF may help minimize the decline in cognitive functions and disease processes that affect cognition and behavior (x).

Lowers Blood Cholesterol

Studies indicate that soy ISF may improve cholesterol levels, specifically LDL cholesterol, which people often label as “bad” or unhealthy (x). Patients with more LDL cholesterol in the blood usually face more significant improvements. Fiber is an essential component in soy ISF that contributes to reducing cholesterol. Soy supplements that contain fiber reduce LDL cholesterol more than twice as much as soy proteins without fiber. Soy ISF helps to lower bad cholesterol levels without affecting healthy HDL cholesterol levels (x).

May Improve Fertility

Soy ISF may improve fertility, especially in female patients. Studies indicate that soy ISF may increase ovulation rates and regulate the menstrual cycle. In addition, women who take soy supplements may have a higher chance of implantation and pregnancy than women who do not take the supplements. It may also help protect cells from BPA and its harmful effects. BPA is a chemical in plastic and it may affect fertility in female patients (x).

Manages Menopause Symptoms

Soy ISF is rich in phytoestrogens that have effects on the body similar to estrogen. During menopause, estrogen levels decrease. Since soy is rich in phytoestrogens, consuming soy foods or supplements may help minimize menopause symptoms (x).

Improves Bone Health

Soy ISF helps minimize bone loss, especially in patients with osteoarthritis. Specifically, it reduces inflammation, which is one of the critical effects of osteoarthritis. Studies that used animal subjects concluded that soy protein significantly reduced swelling and that the subjects tolerated more pain, compared to the subjects that received milk protein. In another study on human subjects, soy protein helped to relieve pain and increase range of motion (x). 

However, the studies also noted that there were different results for male and female patients. The male subjects experienced more beneficial effects than the female subjects, but researchers do not know why these differences may exist (x). 

Similarly, soy ISF may also prevent the onset of osteoporosis, another condition that affects the skeletal system (x). Isoflavones are a type of phytoestrogen, which is a plant compound that has similar activity to the hormone estrogen. A decline in estrogen levels may increase the risk of osteoporosis and osteopenia. Phytoestrogens are also related to calcium, which works with vitamin D to protect and strengthen the bones. Studies suggest that soy isoflavones may help address the risk of these conditions, but the results are inconclusive (x).

Antioxidant Properties

Soy ISF may increase antioxidants in the body, which help manage oxidative stress and eliminate excess free radicals in the body that can cause detrimental health effects (x). Every activity exposes the human body to oxidative stress, which is necessary to bodily functions but in high amounts, it can cause damage to the body’s cells (x).

Too much oxidative stress can trigger various health conditions, which is why it is crucial to include dietary antioxidants to try to minimize its effects. Isoflavones in soy products act as antioxidants that can help prevent oxidative damage in the body.

May Reduce Cancer Risks

Healthy cells usually develop, mature and die off eventually. However, some healthy cells mutate and grow uncontrollably, which is what causes cancer. Soy ISF may help prevent cell mutation and cancer development.

Studies indicate that consuming moderate amounts of soy ISF may lower the risk of cancer, specifically breast and prostate cancer (x). In addition, soy ISF increases PSA levels in men with prostate cancer (x). PSA is a prostate-specific antigen, which is to screening and tracking prostate cancer. Studies show that people in North America, Europe and Australia have higher incidences of prostate cancer than Japan, China and other Asian countries, where soy forms a dominant part of the diet (x).

Research suggests a link between soy protein and uterine or endometrial cancer and unopposed estrogen—a state in which estrogen and progesterone are not balanced properly in the body. A prolonged state of unopposed estrogen may thicken the uterus, which may increase the risk for endometrial cancer. Studies suggest that soy ISF may reduce the risk of endometrial cancer (x).

Benefits of Soy Isoflavone

Side Effects of Soy Isoflavones

Although consuming soy ISF supplements in moderate proportions is generally safe in proper doses, it may cause detrimental effects to overall health. Physicians recommend short-term use—no more than six months.

Soy can cause a wide range of side effects that may affect the digestive system. It can cause bloating, constipation or nausea (x). Patients may also have an allergic reaction with itching or a rash.

It may also be a good idea to avoid soy ISF supplements with hay fever or asthma. Patients with hay fever are more likely to experience a food allergy to soy (x).

Soy ISF may also significantly lower blood sugar levels and affect patients with diabetes. Patients with diabetes or patients that take medication to control blood sugar should avoid this supplement or speak to a physician (x).

Consuming excessive amounts of soy ISF may also increase the risk of kidney stones because the supplement is rich in chemicals called oxalates—the main component of kidney stones. In addition, people with severe kidney disease may be unable to process the chemicals in soy ISF supplements properly, which could increase these chemicals in the body and cause dangerous complications (x).

Similarly, soy ISF has a chemical called phytoestrogens that may be toxic in large amounts. Patients with kidney failure are at a higher risk for dangerously high phytoestrogens if they use soy products. It may also increase the risk of bladder cancer. If a patient has hypothyroidism—an underactive thyroid—soy products may worsen the condition and negatively affect thyroid hormone production (x).

Pregnancy & Breastfeeding

Soy protein is most likely safe for pregnancy and breastfeeding from normal dietary sources. However, medicinal soy products may be harmful and cause complications with fetal development. Large doses may not be safe. Patients who are pregnant or breastfeeding should speak to a doctor before using this supplement (x).


Soy is most likely safe for children in normal amounts from dietary sources. Many infant formula products in the U.S. may also contain soy isoflavones. These formulas are most likely safe as well. They usually do not cause any later health or reproductive complications. However, soy may not be safe as an alternative to cow’s milk if a child has a cow milk allergy. Children with this allergy may also be allergic to soy (x).

Dosage for Soy Isoflavone Powder

Soy products and legume seeds are the most concentrated source of isoflavones. However, it is also present in other sources—cereals, vegetables, fruit, milk, meat and beer (x). While food is an effective source, supplements may also help provide more nutrients and ensure a consistent dosage.

The recommended healthy dosage for soy isoflavone powder is 150 mg per day, with approval from a physician. Always consult with a doctor before starting a supplement regimen. Supplements are not a substitute for medical treatment or medical advice. Instead, they aim to improve a patient’s general health.

The Bottom Line

Soy isoflavones are groups of chemical compounds derived from soy (x). These nutrients play essential roles in maintaining overall health and possibly preventing various diseases. Research associates soy ISF with minimizing menopause symptoms, cardiac disorders, diabetes, osteoarthritis, osteoporosis and even cancer (x). Isoflavones are also antioxidants that help reduce oxidative damage in the body from free radicals.

However, there is also some concern about long-term use, which is why physicians advise short-term use soy ISF for up to six months. It is likely safe, but it may cause some mild side effects, including nausea, bloating or constipation. Patients with asthma or hay fever may be allergic to soy products. Soy is likely safe for pregnancy or lactation in normal dietary sources, but medicinal sources may cause problems with fetal development. It may also pose a risk for patients with diabetes or kidney diseases. Always consult a doctor before taking any supplements, including soy isoflavones. They are not a proper medical treatment, but they may have positive effects on overall health.

Author: James D