What Foods Inhibit Thyroid Function?

Hypothyroidism is a common condition characterized by dysfunction of the thyroid gland, located in the region of the throat. This condition affects over 1 percent of the population and compromises almost all body functions. Symptoms include weakness, fatigue, cold intolerance, weight gain and anemia. Although most instances are due to intrinsic disease of the thyroid or to drugs or iodine deficiencies, foods high in goitrogens can also inhibit thyroid function.

Soy Products

Soybeans, soy extracts and other soy products such as tofu and tempeh contain isoflavones that are associated with decreased thyroid hormone output. Isoflavones reduce thyroid hormone output by blocking activity of the enzyme, thyroid peroxidase, which adds iodine to thyroid hormones. Without this critical step, thyroid hormones cannot be formed. Because thyroid hormones govern the metabolism, symptoms of thyroid insufficiency, including weight gain and lethargy, are those commonly associated with a slow metabolism.

Cruciferous Vegetables

Foods belonging to the cruciferous family include broccoli, cauliflower, Brussels sprouts, cabbage, mustard, rutabagas, kohlrabi and turnips. These foods are also associated with decreased thyroid function. Specifically it is their isothiocyanates, a family of molecules, which like isoflavones, also inhibits the function of thyroid peroxidase and therefore decreases synthesis of thyroid hormones essential to efficient metabolism.

Peanuts

Peanuts are a third food associated with diminished thyroid function. Peanuts are legumes, yet they appear to be the only legume associated with hypothyroidism. As with soy and the cruciferous vegetables, cooking inactivates the goitrogenic compounds in peanuts, but it does not completely eliminate their effects. Many prepared foods are made on machinery that processes peanuts, and many ethnic dishes use peanut oil in their sauces. Ingredients such as hydrolized plant protein may also indicate the presence of peanuts.