Soy and thyroidCan soy cause hypothyroidism? Some foods contain compounds called goitrogens that interfere with thyroid function. In extreme cases these goitrogens can cause goiter (an enlarged thyroid gland). Increasing iodine intake prevents this goitrogenic effect of soy. Some research also indicates that heating soy eliminates part of this goitrogenic effects. Around 1950 there were several cases of goiter in infants fed with soy flour based formulas, which were not fortified with iodine. These formulas do no longer exist and infant formulas are now based on soy protein isolates (not soy flour) and are also fortified with iodine. No cases of goiter have been reported in babies fed with these formulas.
Recent studies indicate that there is little risk to thyroid function in healthy people who consume soy. However, people who have too low intake of iodine could be at risk. Increasing iodine intake is easy: this can be done by using of iodized salt or by taking iodine supplements. According to the American Thyroid Association "soy does not cause hypothyroidism, but it does interfere with the body's ability to absorb thyroid replacement therapy".