The strongest foods in this group [goitrogens] are soy, millet, flax, and cruciferous vegetables. Some nuts and fruits are listed as well, but they generally have a milder effect.
The Strongest Goitrogens are Soy products & Millet:
soy
soy milk
soybean oil
soy lecithin
soy anything
tempeh
tofu
millet (the most goitrogenic food)
Moderate Thyroid Inhibitors – Cruciferous vegetables:
bok choy
broccoli
brussels sprouts
cabbage
cauliflower
garden kress
kale
kohlrabi
mustard
mustard greens
radishes
rutabagas
turnips
Mild Thyroid Inhibitors include:
bamboo shoots
peaches
peanuts
casava
flax
pears
pine nuts
radishes
spinach
strawberries
sweet potatoes
After seeing this long list, don’t panic… supporting the thyroid is about avoiding “excess” consumption of these foods rather than avoiding them altogether. As you are probably aware, many of the foods listed above are very healthy and many are high in nutrients.
In addition to eating moderate amounts of these foods, cooking does help minimize or inactivate the goitrogenic compounds found in these foods (since they are heat sensitive). Cooking cruciferous vegetables does not remove all goitrogens, but it does help. Here’s the breakdown:
If you steam vegetables, it decreases goitrogen yield by about 30%.
If you boil them for 1/2 hr and you keep the water, 65% of the goitrogens are removed.
And if you discard the boiled water, about 90% are removed.
* As a note, fermenting cabbage into sauerkraut actually increases the goitrogens that it contains, but it reduces the amount of nitriles, which is another type of chemical that’s present in some foods like cabbage that has a toxic effect on the thyroid. In fact, nitriles are even more harmful than goitrogens. And unlike goitrogens, the effects of nitriles can’t be offset by iodine intake or iodine supplementation. So with fermentation, you do have an increase in goitrogens, but you have the nitriles, which are even more harmful and not offset by iodine, cut in half. So we might say that the net effect of the fermentation of cabbage and probably other goitrogenic foods is either neutral or even positive because of the reduction of nitriles.
For most people, a small amount of goitrogenic foods are not a problem if you have enough iodine-rich food, or if you’re supplementing with iodine at around 800 mcg (or more) per day [which is a meager .8 mg]. But at high concentrations, goitrogens actually interfere with the incorporation of iodine into thyroid hormone itself, and this means that even if there’s enough iodine in the diet or through supplements going into the gland, it can’t be properly utilized, and therefore, no amount of supplemental iodine would balance the thyroid. Note that people with auto-immune thyroid disease should not supplement iodine as it may make the condition worse.