“I have been reading that certain raw green leafies are bad for your thyroid. I am really concerned about that. I have been eating green smoothies since the latter part of December 2008. Although I have not had problems with my thyroid, I was a bit alarmed with what I read. Please shed some light on that.” – Shawna
Cruciferous vegetables such as kale, bok choy, collards, turnip and broccoli do contain goitrogenic glucosinolates which produce thiocyanates that compete with iodine for absorption by the thyroid gland. Sounds alarming, right?
However, the research also shows that consuming foods that contain glucosinolates does not increase the risk of hypothyroidism unless accompanied by iodine deficiency.
I have consumed three to four cups of raw kale, bok choy or other cruciferous vegetable in my green smoothies since 2008. I recently had routine blood work done, and I checked my thyroid just to see. The lab results indicated that my thyroid function is 100% normal and the numbers are right in the middle of the healthy range.
Basically, if you have a healthy thyroid and adequate dietary iodine intake, you do not need to worry about eating leafy greens from the cruciferous (brassica) faimilies like kale or bok choy.
Sea vegetables are an especially rich source of iodine. Every day, I add a teaspoon or two of dried dulse flakes to my green smoothies. One teaspoon contains 110% RDA of iodine. Kelp is also an excellent source of iodine and you can add kelp powder to green smoothies as well. Neither of these sea vegetables will make your smoothie salty or “fishy”.
Research also suggests that deficiencies of selenium, iron, and vitamin A exacerbate the effects of iodine deficiency. It’s a good thing that cruciferous greens like kale are also rich in iron and beta-carotene (which your body converts to vitamin A). As for selenium, keep some Brazil nuts on hand. Just one nut per day will provide adequate selenium in your diet.
There are nutrients and anti-nutrients (toxins) in all foods that you eat, including fruits and vegetables. As long as you eat whole foods and keep an eye on your nutrient intake, you don’t have much to worry about.
As a precaution, I also recommend rotating your greens. I wouldn’t stuff 3 or 4 bunches of kale each day into green smoothies. Over time, that could cause a problem. You wouldn’t want to overload your body with one particular anti-nutrient that may contribute to a nutrient imbalance. (Read more on How and Why You Should Rotate Your Greens.)
If you do suspect that you have impaired thyroid function, be sure to get tested and work with a nutritionally trained medical practitioner who can help you establish a diet that will help support and improve thyroid function.
If your thyroid is healthy, there’s no need to eliminate (or cook) kale or other raw cruciferous vegetables.
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Tracy Russell is the creator of the Green Smoothie Health & Weight Loss Program and founder of Incredible Smoothies. She is passionate about helping people improve their health with green smoothies and a whole foods lifestyle.