Myth: Soyfoods can lead to hypothyroidism.
Soy does not adversely affect thyroid function in healthy people and does not need to be avoided for those taking medication for hypothyroidism.
More than 20 clinical studies show that isoflavones do not adversely affect thyroid function in healthy people. This research includes multi-year studies in which participants consumed large amounts of soy.
Messina M, Redmond G. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid 2006;16:249-58.
Bitto A, Polito F, Atteritano M, et al. Genistein aglycone does not affect thyroid function: results from a three-year, randomized, double-blind, placebo-controlled trial. J Clin Endocrinol Metab