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The Iodine Group | |
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Goitrogenic Foods
There are two primary categories of food that are commonly seen as goitrogenic: (1) soy products and (2) vegetables of the Brassica family (e.g., broccoli, cauliflower, kale, cabbage, collard greens, kohlrabi, radish, turnips, mustard greens, Brussels sprouts, and rutabagas).
Soy. Isoflavones -- especially genistein -- in soy block TPO (Thyroid Peroxidase), an enzyme critical to the transformation process that results in the creation of thyroid hormones from iodide.
Brassica. Isothiocyanates in the Brassica vegetables also block TPO. The cyanogenic glucosides, glucosinolates, and thiocyanates all seem to be important. Thiocyanates block the NIS symporter, interfering with iodide uptake to the thyroid and breast (keeping the iodide from the breast milk).
Other foods. A variety of other foods are also generally seen as goitrogens: e.g., millet, rape seed (Canola Oil), pine nuts, peanuts, cassava, bamboo shoots.
Goitrogens are also found in clover and alfalfa (biochanin A -- a TPO inhibitor), grasses, and water. Goitrogens eaten by animals can affect the iodine in animal products such as milk, butter, cheese, eggs, meat, etc.
Factors mediating the effects of goitrogens. Unfortunately, research has not yet firmly established exactly what compounds are goitrogenic, how they operate, and how best to deactivate them.
Cooking seems to reduce the chemicals in the Brassica family, but does not eliminate them. Fermentation is also thought to affect these chemicals, but it is not clear exactly what is happening nor how effective it is.
The effects of these chemicals is significantly worse if iodine is deficient. However, adequate iodine does not seem to completely protect against them.
Moreover, the effects on TPO do not seem to fully explain what is happening, since blocked TPO does not always result in reduced thyroid function.
Other effects of goitrogens. In addition to their effects on goiter, hypothyroidism, and hyperthyroidism, goitrogenic foods also appear to be related to thyroid cancer and autoimmune thyroid diseases (Fort).
Goitrogen Research
Chandra, et al have researched plants containing cyanogenic goitrogens (glucosinolates, glucosides, and thiocyanates). When studying radishes (a cruciferous plant containing cyanogenic goitrogens), they found (1) increased weight of the thyroid gland, (2) decreased thyroid peroxidase activity, (3) reduced thyroid hormone profiles and (4) elevated level of thyrotropin -- even after supplementation of adequate iodine.
Daniel has written a highly recognized book on soy that includes useful information on the goitrogens found in soy: isoflavones and saponins.
Doerge has established that soy isoflavones and many dietary flavonoids inhibit TPO.
Gaitan, et al, have researched a variety of antithyroid compounds and environmental goitrogens. They have presented strong evidence that C-glycosylflavones in millet inhibits TPO. They have investigated antithyroid effects of babassu and mandioca and the goitrogenic effects of coal-water extracts. They have also looked at the antigoitrogenic effect of casein.
Mary Shomon has written on the glucosinolates in vegetables that act as goitrogens.
Masterjohn discusses goitrogenic foods, including soy, millet, cruciferous vegetables, cassava, lima beans, flax seeds, almonds, and fruits and fruit seeds of the Rosacea family. Especially interesting is his discussion of the effects of cooking and fermenting.
Elnour discusses millet as a goitrogen.
Kaplan discusses the goitrogens that create problems for green iguanas.
See lots more goitrogen research on the left.
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