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 milk
- soybean oil
- soy lecithin
- soy anything
- millet (the strongest thyroid-suppressing food)
Moderate Thyroid Inhibitors – Cruciferous vegetables:
- bok choy
- brussels sprouts
- garden kress
- mustard greens
Mild Thyroid Inhibitors include:
- bamboo shoots
- pine nuts
- sweet potatoes
After seeing this long list, don’t worry! Supporting the thyroid usually means 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, these foods theoretically only reduce thyroid function if there is an iodine deficiency (more on iodine below).
Start by eating only moderate amounts of these foods, then consider that 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 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 – as long if you have enough iodine in the diet. But at high intake levels, goitrogens actually interfere with the incorporation of iodine into thyroid hormone itself. When this happens, iodine can’t be properly utilized, and therefore, no amount of supplemental iodine will balance the thyroid. (Note that people with auto-immune thyroid disease should not supplement iodine as it may make the auto-immune condition worse)
There are also chemical substances which can have a goitrogenic effect on the 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
- Eat a high protein breakfast to support thyroid function. Try to get around 30 grams of protein from a high quality animal or vegetarian source.
- Establish regular cycles for sleep, work and meals. This will support the adrenals, which in-turn support the thyroid.
- 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.
- 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.
- High Estrogen levels may also inhibit thyroid function. Consider measuring your estrogen levels if you suspect you have an estrogen excess