America’s obsession with raw kale is at an all-time high – raw kale juices, smoothies, kale chips, kale salads – the options are endless. The green, leafy vegetable is packed with nutrients: just one cup provides 9% of the daily value of calcium, 206% of vitamin A, 134% of vitamin C, and a staggering 684% of vitamin K. A one cup serving also provides nearly 3g of dietary fiber, and is packed with carotenoid and flavonoids which are thought to help prevent cancer. Plus, around 80% of kale is comprised of water, thus the calorie count comes in at only 33 kcal per cup.
With all of these great health benefits, it was pretty disheartening to see the New York Times headline last January, “Kale? Juicing? Trouble Ahead.” Is there really a negative side to this beloved veggie? Here is an excerpt from Jennifer Berman’s opinion article in the NYT:
Imagine my shock, then, at my last physical, when my doctor told me I had hypothyroidism, common in women over 40. When I got home I looked up the condition on the Internet and found a list of foods to avoid: Kale, which I juiced every morning, tops the list, followed by broccoli, cauliflower, cabbage, Brussels sprouts and collard greens – the cruciferous vegetables I consumed in large quantities because they are thought to prevent cancer”
Could consuming large doses of kale and other cruciferous vegetables really lead to hypothyroidism? The answer: Maybe.
The connection with the thyroid is that in addition to their healthy compounds, cruciferous vegetables, like kale, also contain isothyocynates and goitrogens. These substances suppress the function of the thyroid gland by interfering with iodine uptake – decreasing the amount of thyroid hormone produced and resulting in under-active thyroid or hypothyroidism. Symptoms of hypothyroidism include fatigue and weight gain, as a result of a slowly decreasing metabolism.
However, unless you are predisposed to low thyroid, have low iodine intake, or are consuming huge amounts of raw, cruciferous veggies every single day, these results are not likely. And certainly, if you already have hypothyroidism or are taking thyroid medication, you should check with your doctor about what is safe to consume. Reasonable amounts should not be a problem.
Still worried? Here are a few tips to safely enjoy kale:
1. Cook your kale. The goitrogenic properties of kale and other cruciferous vegetables are greatly reduced when cooked. Cruciferous vegetables include the following among others:
- Bok choy
- Brussels sprouts
- Collard greens
2. Make sure you are getting enough iodine. In America, table salt is fortified with this nutrient, so deficiencies are rare.
3. Mix it up. Every other day, swap kale or other cruciferous veggies for a non-cruciferous variety. Bell peppers, zucchini, carrots, and asparagus are just a few that are also nutrient dense but don’t have the same goitrogenic properties.
Bridgette Kidd, MPH, RD
Healthy People Program Specialist, Family and Consumer Sciences
Ohio State University Extension
Lisa Barlage, MS
Extension Educator, Family and Consumer Sciences
Ohio State University Extension
Berman, J. Kale? Juicing? Trouble Ahead. New York Times. 2014 Jan.
Higdon, J. Cruciferous vegetables. Oregon State University Linus Pauling Institute. 2008 Dec. Available at: http://lpi.oregonstate.edu/infocenter/foods/cruciferous/
National Cancer Institute. Cruciferous vegetables and cancer prevention. 2012. Available at: http://www.cancer.gov/cancertopics/factsheet/diet/cruciferous-vegetables
United States Department of Agriculture. National Nutrient Database for Standard References. Available at: http://ndb.nal.usda.gov/ndb/foods/show/3030
Sede Wes says
Hello, I believe that thiocyanate ions are the issue with thyroid function, not isothiocyanates. My understanding is that isothiocyanates are bery beneficial to our health. Source:
Regards, Sede Wes