Thyroid Inhibiting (Goitrogenic) Foods

Goitrogens are plant chemicals (thiocyanate) that can decrease the production or activation of thyroid hormone, meaning they slow thyroid function.  These foods are commonly known as “Goitrogenic”, which means they contain substances which slow the thyroid’s ability to uptake iodine.  If eaten in excess, these (otherwise healthy) foods interfere with the efficient function of your thyroid gland.  For some people, eating too much of these foods alone will produce a hypothyroid state.  At its extreme, the Goitrogenic effects makes you susceptible to having a goiter, or enlargement of the thyroid.

The strongest foods in this group 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:

  1. If you steam vegetables, it decreases goitrogen yield by about 30%.
  2. If you boil them for 1/2 hr and you keep the water, 65% of the goitrogens are removed.
  3. And if you discard the boiling water, about 90% are removed.

* As a note, fermenting or culturing these foods, as done with sauerkraut or kimchi, actually increases the goitrogenic effects.  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.  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.

There are also certain chemicals which can have a goitrogenic effect on your thyroid function.  They include:

Mercury, fluoride, chlorine, bromides, Amiodarone, carbamazepine, iopanoic acid, Lithium, phenobarbitone, phenytoin, potassium perchlorate,propylthiouracil, rifampin, sulfadimethoxine, and SSRI’s like Celexa and others

Based on the list above, below are some additional recommendations:

  1. Consider getting tested for mercury levels.  This is especially important if you have mercury amalgams or if you have some known exposure, including high mercury fish consumption.
  2. Use a double filtration water system in your home to remove chlorine and fluorine from your drinking water.  Some experts say that you can absorb a large amount of chlorine and fluorine gas during a shower, so it may be wise to get a water filter on your shower as well.
  3. High Estrogen levels may also inhibit thyroid function.  Consider measuring your estrogen levels if you suspect you have an estrogen excess.




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