In an article for The New York Times, Jennifer Berman reports on the problems with kale:
“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.”
This is based on a study by Oregon State:
“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.”
Q:What should you do?
A: Avoid juicing with kale and most importantly cook kale.
“The goitergenics 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, horse radish, radish, wasabi and watercress are also cruciferous vegetables.)”
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