Recent studies suggest that soy can have a negative effect on thyroid function. Soy can impair your thyroid’s ability to absorb iodine. So the risk of developing hypothyroidism significantly increases if you have an iodine deficiency.
However, there are also other researchers who say that if you limit your soy intake and don’t have a pre-existing iodine deficiency, then your risk of developing an underactive thyroid is quite low. Men especially should eat soy in moderation because soy is known to mimic estrogen in the body.