Some foods contain goitrogenic substances that reduce the utilization of iodine. These foods include canola oil, vegetables from the Brassica family (eg, cabbage,154 brussels sprouts,155 cassava,156 and millet157). The actual content of goitrogens in these foods is relatively low, however, and cooking significantly reduces the impact of these goitrogens on thyroid function.158
Studies show conflicting information concerning the impact of soy on the thyroid. Isoflavone molecules in soy do inhibit an enzyme involved in thyroid hormone synthesis,159,160 but that has not translated into poor thyroid function in otherwise healthy individuals with adequate iodine intake.161,162,163
For those with hypothyroidism, raw goitrogenic foods and soy foods that have not undergone fermentation and/ or food processing should be consumed in moderation and discontinued if symptoms should appear.