The headline in The New York Times made my heart sink: “Kale? Juicing? Trouble Ahead.”
Confession: I’m one of those Vitamix-loving, green-smoothie worshipping, kale bandwagoners. I brim with holier-than-thou pride when my kids eat raw kale (no dressing, even!) and thick kale-laden shakes while other children snack on sugary GoGURT squeezes and suck on juice boxes.
I am not alone. Presidents and stars are kale-lovers too.
Kale, in case you haven’t noticed, is health-conscious America’s “it” vegetable. Raw, blended, sauteed or in chip or “crunch” form, it appears to be the manna of celebrities: Gwyneth and Jennifer devour it while Kevin Bacon recently declared [it's] “the age of kale.” In an astutely reported feature called “Stars Who Love Kale,” US Weekly quotes Bette Midler saying: “Kale is burning up the veggisphere.”
Even the Obamas dined on kale salad at their Thanksgiving feast, notes The Washington Post.
But apparently there’s trouble in cruciferous paradise.
Writing for The Times, Jennifer Berman reports on the dark side of kale, and how the health-infused, veggie Eden she’d carefully built over years began to crumble:
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, which runs in my family. And flax — as in the seeds — high in omega 3’s, that I sprinkled on cereal and blended in strawberry almond milk smoothies. Also forbidden: almonds and strawberries, not to mention soy, peaches, peanuts, corn, radishes, rutabaga and spinach.
My first reaction: Berman must be misguided, mistaken. Can kale possibly be bad?
Well, yes, possibly. Here’s the science-y lowdown on the kale-thyroid connection from the Oregon State University Micronutrient Information site:
Very high intakes of cruciferous vegetables…have been found to cause hypothyroidism (insufficient thyroid hormone) in animals (68). There has been one case report of an 88-year-old woman developing severe hypothyroidism and coma following consumption of an estimated 1.0 to 1.5 kg/day of raw bok choy for several months. Two mechanisms have been identified to explain this effect. The hydrolysis of some glucosinolates found in cruciferous vegetables (e.g., progoitrin) may yield a compound known as goitrin, which has been found to interfere with thyroid hormone synthesis. The hydrolysis of another class of glucosinolates, known as indole glucosinolates, results in the release of thiocyanate ions, which can compete with iodine for uptake by the thyroid gland. Increased exposure to thiocyanate ions from cruciferous vegetable consumption or, more commonly, from cigarette smoking, does not appear to increase the risk of hypothyroidism unless accompanied by iodine deficiency. One study in humans found that the consumption of 150 g/day (5 oz/day) of cooked Brussels sprouts for four weeks had no adverse effects on thyroid function.
(For an updated reality check on kale consumption and the thyroid, see our Q and A with endocrinologist and thyroid expert Dr. Jeffrey Garber here. Bottom line: in the U.S, where we don’t have a big problem with iodine deficiency, it’s probably OK.)
Teresa Fung, Sc.D., M.S.. an adjunct professor of nutrition at the Harvard School of Public Health and a professor at Simmons College in Boston, confirms the kale-thyroid link. But, she says, “normal, reasonable amounts of eating should not be a problem. A regular person [with no thyroid issues] who eats several servings of cruciferous vegetables a week should not have problems.”
Fung adds: “It’s the dose that makes a poison. If people have hypothyroidism or they’re taking thyroid medication, then they should check with their doctor. But even in this case, reasonable amounts shouldn’t be a problem. Now, if people have a tall glass of kale juice every single day, then it gets into the unknown territory.”
So, what are still-anxious kale-lovers to do? I asked Somerville, Mass. health coach and psychology of eating coach Nina Manolson to offer some guidance. (She’s not a doctor, but she knows a lot about food, so keep that in mind and always check with a professional if you make major changes in your diet.)
Nina reiterated that kale is a goitrogenic food, meaning that it can contribute to an enlarged thyroid — a goiter. A goiter indicates that the thyroid gland is not functioning optimally. But, she says, there are ways to have our kale and eat it too. Here, lightly edited, are her suggestions:
1. Cook Your Kale
The goitrogenic properties of kale become dramatically lessened when kale — or any other cruciferous vegetable — is cooked. (Other veggies in this category include: broccoli, brussel sprouts, cabbage, cauliflower, collard greens, kohlrabi, mustard, rutabaga, turnips, bok choy and Chinese cabbage. Arugula, horseradish, radish, wasabi and watercress are also cruciferous vegetables.) Continue reading