A goitrogen is a substance that suppresses thyroid function by inhibiting iodine uptake. Goitrogens get their name because of their tendency to cause goiter, swelling of the thyroid gland.
Some foods can be goitrogenic when they’re eaten in excess, or if the individual has a background of low iodine uptake. Goitrogenic foods include: cassava, which is otherwise known as yucca; soy products; millet; sweet potatoes; cruciferous vegetables like cabbage, broccoli, Brussels sprouts, cauliflower, bok choy; and most dark leafy greens like kale and mustard greens.
Goitrogens can actually decrease the uptake of iodine in the thyroid gland from other foods that we eat that contain iodine. When eaten regularly (a few times a week), or eaten raw, these foods can impact your thyroid function. Goitrogens interfere with the manufacturing of the thyroid hormone. Even if there’s enough iodine going into the thyroid gland, it can’t be properly utilized and no amount of supplemental iodine — either through food or supplements — will be able to overcome a large intake of goitrogens.
In the case of someone with hypothyroidism, over time, consuming high rates of goitrogenic foods, such as raw kale in green smoothies, can inhibit iodine uptake, actually making their thyroid condition worse.
For the individual with hypothyroidism, kale and collard greens are the biggest offenders. Other green leafy vegetables aren’t as high in goitrogens, and may not have such a severe effect on thyroid function.
Cooking method can also reduce the goitrogen content of foods. For example, steaming foods like kale, broccoli and other cruciferous vegetables can reduce goitrogen content by as much as 33 percent, which can make a big difference, especially if these foods are eaten regularly.
Top Goitrogenic Foods
- Bok Choy
- Brussel sprouts
- Mustard and Mustard greens
Goitrogenic activity can be identified through lab testing, watching specifically for conversion of T4 to T3, which would indicate possible goitrogenic activity. Test TSH, T4, and T3 and again after a month to look for any changes in those markers.
Although green smoothies can be very healthy, for the individual with thyroid problems, consuming raw green smoothies every day is not a good idea. Rotating greens and increasing variety in your foods is best. If you do eat green smoothies, watch for a return of thyroid symptoms as a possible sign of excess goitrogens.
Betty Murray, CN, IFMCP, CHC is a Certified Nutritionist & Certified Functional Medicine Practitioner with the Institute for Functional Medicine, founder of the Dallas-based functional medicine clinic Living Well Dallas and Executive Director of the the Functional Medicine Association of North Texas. A master of the biochemistry of the body, Betty teaches her clients how to utilize nutrition for autoimmune diseases, digestive disorders, MTHFR and weight loss. You can find her book “Cleanse: Detox Your Body, Mind & Spirit” on Amazon here.
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