Soy & Thyroid Levels

Soy foods serve as the only common plant-derived food source of complete proteins, meaning the protein contains all of the essential amino acids. This makes soy a common food choice for vegetarians. Soy also contains carbohydrates, unsaturated fats and fiber as well as vitamin and nutrients. Despite the nutritional benefits of soy, research such as that published by Diamanti-Kandarakis in the 2009 "Endocrine Reviews" suggests that compounds found in soy foods can adversely affect the level of thyroid hormones.

Thyroid

The thyroid is a gland in the neck responsible for the production of two hormones; thyroxine and triiodothyronine. Once secreted, these hormones travel through the bloodstream to affect nearly every type of cell in the body. Thyroid hormones help regulate metabolism, the amount of oxygen used and therefore the amount of calories burned over a specific time.

Hormone Production

Thyroid cells absorb iodine from food sources, such as iodized salt. The iodine then combines with the amino acid tyrosine. The enzyme thyroid peroxidase facilitates this chemical reaction necessary for the production of the hormones. A hormone produced by the pituitary gland known as thyroid stimulating hormone regulates this process, helping to ensure adequate levels of thyroid hormone.

Soy Compounds

Foods derived from soybeans contain a compound known as isoflavones. Isoflavones are classified as phytoestrogens for their ability to induce effects similar to the hormone estrogen. Once consumed the natural form of the isoflavones breaks down into the active forms, including genistein, daidzein and glycitein.

Effect on Thyroid

The isoflavones found in soy inhibits the activity of the enzyme thyroid peroxidase. Inhibiting this enzyme reduces the ability of the thyroid cells to absorb iodine and combine it with tyrosine to form thyroid hormones. Eating large amounts of soy foods can inhibit the production of thyroid hormones enough to cause hypothyroidism -- a condition characterized by low levels of thyroid hormone. Soy foods most likely affect those who also suffer from an iodine deficiency, according to the Oregon State University Linus Pauling Institute.

Soy And SyntheticThyroid Hormones

If you currently take synthetic thyroid hormone medication to treat hypothyroidism, doctors at the Mayo Clinic warn that eating soy may interfere with the absorption of your medication. This interference may decrease the effectiveness of the medication allowing your symptoms, such as fatigue, cold intolerance and depression, to continue. They suggest taking the medication on an empty stomach and waiting at least four hours before consuming any soy products.