Does Kale Affect Thyroid Function? What You Should Know...

The latest in Kale Trends

For the past 5 or so years, I’ve seen the garnish I avoided like the plague on the plates of chicken tenders I ordered at restaurants as a child gaining immense popularity. It seems like nowadays you can’t browse a menu or get out of Whole Foods without encountering at least some form of kale. In the health food industry, kale is everywhere! You’ll find it in green smoothies, juices, salads, and any number of recipes in a modern cookbook. It’s arguably currently the nation’s most popular vegetable and has definitely won me over since the days I was ignoring it on my plate at Red Lobster. But recently, I’ve seen a darker trend growing in kale—and I’m not talking about leaf color.

In the past month a few friends have shared articles with me describing the relationship between kale and hypothyroidism, even implicating kale and other foods commonly considered healthy as the cause of hypothyroidism. As the thyroid disorder is a concern for women over age 40 in the U.S., and many of our patients complain of symptoms of the condition, or seek treatment with us if diagnosed, and as I wasn’t ready to give up one of the staples of my favorite green juice—I decided the relationship between kale and thyroid function was something to look into.

Kale is a cruciferous vegetable, a group of foods unique in that they are rich sources of chemical compounds known as glucosinolates. The list of glucosinate-producing foods includes many that are commonly considered healthy: spinach, peanuts, soy, bok choy, cabbage, chard, broccoli and cauliflower, to name a few. Glucosinolates are able to form a substance called goitrin that can suppress the function of the thyroid gland by interfering with iodine uptake, which can, as a result, cause an enlargement of the thyroid. One thing to keep in mind if this sounds like a red flag, is that iodine-deficiency is extremely uncommon for anyone consuming an American diet, since the introduction of iodized salt in 1920. It’s virtually unavoidable in processed food (Gans, 2014).

Conversely, the glucosinolates in cruciferous vegetables are also considered valuable antioxidants, meaning that they are able to help prevent cancer. Kale, specifically, is known to help combat at least 5 types of cancer: including cancer of the bladder, breast, colon, ovary, and prostate. Isothiocyanates (ITCs), which are actually made from the glucosinolates in kale—the very components under scrutiny—play a primary role in achieving these risk-lowering benefits. Kale is also known to assist in the body’s natural detoxification processes at a genetic level (The George Mateljan Foundation). Unless consumed in ostensibly large quantities (perhaps more than 3 lbs a day), cruciferous vegetables should not cause thyroid issues in individuals with thyroid function of normal range. In Traditional Chinese Medicine (TCM), kale is also considered a warming food, and recommended for people who have too much “cold”; it’s a winter vegetable.

So what does the fact that kale is potentially goitrin-producing tell us? Is it never to eat kale and other nutrient-dense vegetables like bok choy, cabbage, and broccoli and again? Certainly not.

Rather, re-evaluate high levels of kale and cruciferous veggie consumption if you already have a diagnosis of hypothyroidism or other thyroid condition that can be negatively impacted by goitrogens.

One important practice to consider when choosing foods in general is to keep a varied diet. If you’re a veggie juicer like me, make sure to rotate your greens each week to best juice the maximum health benefits out of each! Kale is a potassium powerhouse, chard is iron-dense and spinach is rich in manganese and folate. If you’re used to mostly eating raw, look into cooking your cruciferous vegetables. Cooking makes them easier on the body by allowing you to expend as little energy as possible on warming and digesting your food, and may also inactivate some of the potentially goitrogenic substances. Steaming in particular helps kale to better bind to the bile acids of the digestive tract, resulting in a lowering of one’s overall cholesterol levels (The George Mateljan Foundation). In TCM, cooking is recommended for preparing most vegetables.

As always, check in with your practitioner if you have concerns, and refer to our fertility foodie diet before heading to the grocery store or planning a menu. We’ll always strive to keep you up to date on what’s #trending with kale.

Article Resources:

Gans, Keri. “Could Kale Cause Hypothyroidism.” Shape. 13 January 2014. Accessed February 2014. Web. 3 February 2014.

Kale. The George Mateljan Foundation. ND. Web. 3 February 2014.

Additional Resources:

Bruno, Jerry. "What Are All the Benefits of Kale? And Can You Eat Too Much?" Thrive Cuisine. 21 March 2017.