Goitrogens are substances that suppress the function of the thyroid gland by interfering with iodine uptake. Those with autoimmune thyroid disorders (Hashimoto’s thyroiditis or Grave’s disease) and those with low thyroid function (which can often accompany other autoimmune diseases) are often advised to avoid consumption of cruciferous vegetables, spinach, radishes, peaches and strawberries due to their goitrogenic properties.
The thyroid produces hormones that have essential roles in metabolism and even in regulation of the immune system, so supporting optimal thyroid function in everyone is important for healing and for general health. Avoidance of these “goitrogenic” foods is not justified in all instances. The focus is on the need to create a right fit between each person's diet and the nutrients needed by his or her thyroid for optimal function.
Truly, the most important aspect of supporting thyroid function is providing the necessary minerals for thyroid hormone production, the most important of which are iodine, iron, selenium and zinc. Deficiencies in any one of the minerals may impair thyroid function, but the effect of deficiencies is greatly magnified when more than one of these minerals are not available in adequate quantities.
The cruciferous family of vegetables (a.k.a. brassicas) comprises many of the most antioxidant-, vitamin- and mineral-rich vegetables available, including:
Cassava and Cabbage, soybeans (and soybean products such as tofu, soybean oil, soy flour, soy lecithin), pine nuts, peanuts, flax seed, millet, strawberries, pears, peaches, spinach, bamboo shoots, sweet Potatoes
Vegetables in the genus Brassica; Bok choy, broccoli, Brussels sprouts, cabbage, canola, cauliflower, Chinese cabbage, collard greens, horseradish, kale, kohlrabi, mizuna, mustard greens, radishes, rapini, rutabagas, turnips
Despite being generally a stimulant, caffeine acts on thyroid function as a suppressant. Some studies on rats suggest that excess caffeine in conjunction with a lack of iodine may promote the formation of thyroid cancers.
And some foods and drinks have an opposite effect on the thyroid gland; that is, they stimulate thyroid function rather than suppressing it, examples being avocado and saturated fat.