Soy Isoflavones & Thyroid



Soy foods, those derived from the soybean, contain compounds known as isoflavones. In the plant the soy isoflavones are bound to a sugar molecule creating a compound known as glycosides. Once ingested, the process of digestion releases the sugar portion creating an isoflavone aglycone that can trigger responses within the body. In addition to inducing mild hormone-like activity, isoflavones can affect thyroid function.


Thyroid Gland

Stimulated by thyroid stimulating hormone, TSH, produced by the pituitary gland, the thyroid gland absorbs iodine and combines it with the amino acid tyrosine to produce the two thyroid hormones — thyroxine also referred to as T4 and triiodothyronine, known as T3. The thyroid hormones then travel throughout the body to regulate each cell’s metabolism, the process by which oxygen converts into energy. Because thyroid hormones affect all cells, and therefore all bodily systems, problems with the thyroid can cause a variety of symptoms.

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Thyroid Problems

Thyroid problems are common, especially problems that cause hypothyroidism — too little thyroid hormone, or hyperthyroidism — too much thyroid hormone. Hyperthyroidism causes the body’s metabolism to increase resulting in weight loss, irregular heartbeat, sweating, nervousness and irritability. Hypothyroidism causes the metabolism of the body to slow down leading to obesity, joint pain, infertility and heart disease.


Effects of Soy

Soy isoflavones can inhibit the activity of the enzyme known as thyroid peroxidase, or TPO. Cells in the thyroid gland need TPO to extract the iodine from foods and produce thyroid hormones. Eating large amounts of soy products can therefore inhibit the production of thyroid hormones leading to hypothyroidism. In addition, the presence of isoflavones can cause the thyroid to become inflamed, a condition known as goiter, to allow for additional blood to flow through in an attempt to extract more iodine. However, the Linus Pauling Institute indicates that eating soy products fails to produce a negative effect on the thyroid gland as long as iodine intake remains sufficient.


Iodine Intake

In order to prevent soy foods from negatively affecting your thyroid be sure to consume enough iodine in your diet. The main source of dietary iodine is iodized table salt. Since the addition of iodine to table salt the incidence of iodine deficiency became rare in the United States and other developed countries, according to the University of Maryland Medical Center. The National Institutes of Health Food and Nutrition Board recommend that adults consume 95 mcg of iodine per day.


Soy and Thyroid Medications

If you suffer from hypothyroidism your doctor will likely prescribe synthetic thyroid hormones to boost the missing hormone levels and reduce symptoms. The soy isoflavones in soy food products may interfere with the absorption of the medication. To prevent this interaction, suggests taking the thyroid hormone on an empty stomach and waiting at least four hours before consuming soy products.


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About this Author

Stephanie Chandler is a freelance writer whose master’s degree in biomedical science and over 15 years’ experience in the scientific and pharmaceutical professions provide her with the knowledge to contribute to health topics. Chandler has been writing for corporations and small businesses since 1991. In addition to writing scientific papers and procedures, her articles are published on, and other websites.

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Soy Isoflavones & Hot Flashes

Soy Isoflavones & Hot Flashes



Hot flashes are one the most common symptoms of menopause, with three out of four menopausal women experiencing them. Traditionally, hot flashes have been treated with synthetic estrogen in the form of hormone replacement therapy, or HRT. More women are looking for natural alternatives to HRT because of the downsides of synthetic hormones. Research published in the October 2010 issue of the Journal of the American Medical Association found an increase in breast cancer in postmenopausal women who take the synthetic estrogen and progesterone contained in HRT. Soy isoflavones, found in the soy foods we eat, are believed to provide the same benefits as the estrogen that is naturally produced in the body.

Hot Flashes

The cause of hot flashes is still unknown, according to the North American Menopause Society. The sharp decrease in estrogen concurrent with menopause is believed to initiate a chain of reactions that begins in your hypothalamus, the part of the brain that controls body temperature. The hypothalamus reacts as if your body is too warm and triggers dilation of blood vessels near the surface of the skin. This dilation shows up as a flushed feeling or a hot flash.



Soy Isoflavones

Soy Isoflavones are chemical compounds called flavonoids that are found in soybeans. They are also called phytoestrogens, meaning plant-derived compounds with estrogen effects. When ingested, they function as weak-estrogens by binding to estrogen receptors. Your body has cells with estrogen receptors located in the reproductive organs, brain, liver and fat cells.

The three most common types of isoflavones in soybeans are called genistein, daidzein and glycitein. The chemical structure of these compounds is similar to estrogen, but they are not estrogen molecules. However, they are close enough that they will bind with estrogen-sensitive cells. This will give you the benefits of estrogen at a much lower potency and without the drawbacks of the synthetic hormones found in HRT.



Isoflavones are found in varying amounts in soybeans and soybean products. According to the U.S. Department of Agriculture-Iowa State University Database, soy flour is rich in isoflavones, with 177.89 mg per 100 g. Soy protein isolate is extracted from soybeans and contains 97.43 mg isoflavones per 100 g. Raw soybeans vary in the amount of isoflavones based on the type of soybean. Taiwan soybeans have 59.75 mg isoflavones per 100 g; Korean soybeans have 144.99 mg per 100 g and Japanese soybeans have 118 mg per 100 g.

Other soy products containing isoflavones are tofu, tempeh, miso, soy cheeses and soy yogurt.



Some women experience an improvement in the number and intensity of hot flashes after adding soy isoflavones to their diets. According to the February 2006 issue of the American Family Physician, soy isoflavones reduced hot flashes by 9 percent to 40 percent in some trials. However, not all women receive the same results. In Japan, a study of 1,106 women ages 35 to 54 with menopausal hot flashes found that soy isoflavones in the diet had a protective effect against hot flashes. The study was published in the American Journal of Epidemiology.



Always seek advice from a medical doctor before proceeding with soy isoflavone supplements and foods. Although menopause is a natural transition in life, talk with your health care professional about your specific conditions. Some women may have allergies to soy and should be evaluated by a medical professional.

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About this Author

Deila Taylor received a bachelor’s degree in biochemistry from Occidental College with graduate work at USC in pharmacology and nutrition as well as coursework at The East West School of Herbology. She is a small business owner in the alternative energy field.

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