In the last 10 years, soy foods have dramatically increased in popularity. From soy milk in coffee shops to the array of soy meat products available at grocery stores, consumers are buying more soy. "Soya" is a term often used to describe the whole soybean, while the term "soy" is used to describe products that contain soybeans. They are often used interchangeably, however. Recently, concerns have arisen over the consumption of soy and the effects of it on the thyroid gland and on hypothyroidism medications.
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What is Soy?
Soy foods are produced from soybeans, also known as edamame. Soybeans grow on plants in a green pod. Common soy products include soy milk, tofu, tempeh, miso, soy cheese and soy meats. The U.S. Food and Drug Administration states that foods containing soy protein may help reduce coronary heart disease. The FDA determined that individuals who consume 25 g of soy protein a day as part of a low saturated fat and cholesterol diet, may reduce their risk of heart disease by improving blood cholesterol levels.
Functions of the Thyroid Gland
The thyroid gland sits below your larynx. It is a small gland weighing less than an ounce that has a butterfly shape. The wings of the thyroid gland wrap around the front of your trachea. This small gland carries an important function. The thyroid produces and releases hormones that control the speed and efficiency by which cells convert nutrients from ingested food into energy. The cells require this energy to function. Therefore, the thyroid impacts every cell, tissue and organ in the human body. This efficiency rate is also referred to as your body's metabolism.
An Underactive Thyroid
When you have a healthy thyroid, it produces enough hormones to keep the cells in your body running efficiently. When something interferes with the function of the thyroid gland, however, it may cause it to produce too much or not enough hormones. According to Harvard Health Publications, outside influences such as some medications or disease can interfere with the communication between the thyroid gland and the rest of the body. When this happens, it can cause the thyroid to not produce enough hormones, a condition known as hypothyroidism, or underactive thyroid. The disconnect would also cause the thyroid to produce too much hormone and cause hyperthyroidism, or an overactive thyroid.
Soy's Effect on the Thyroid
According to the Physician's Committee for Responsible Medicine, clinical studies conclude that soy products do not cause hypothyroidism. Soy is a phytoestrogen, however; therefore, it can act in the body in similar ways as a hormone. The isoflavones found in soy can absorb some of the iodine that would normally go to the thyroid gland to make thyroid hormones. Iodine effect also occurs with fiber supplements and some medications. The highest amount of soy isoflavones are found in soy nuts and tempeh. Most individuals in industrialized countries get plenty of iodine in their diet. If you consume a lot of soy products, you may need to consume slightly more iodine than the recommended daily values.
Soy's Effect on Hypothyroid Medications
Another concern with soy is that it will have adverse effects on hypothyroid medication. Hypothyroidism is usually treated with synthetic thyroid hormones. Soy as well as high-fiber foods, iron supplements, certain antacids and calcium supplements can interfere with the body's ability to absorb the medication. This does not mean, however, that individuals on the medication should avoid soy completely. The University of Maryland Medical Center recommends people with thyroid problems talk to their doctor about consuming soy.