Kale might be bad for you in some cases — here's when you should be careful about eating it

Woods Wheatcroft / GettyIt’s probably a good idea to wash your kale.
  • Kale is packed full of things that are good for you like protein, vitamin A, and vitamin K.
  • But if you have an underactive thyroid, it might be a good idea not to eat too much of it.
  • Certain compounds in the vegetable can interfere with thyroid hormone synthesis and essentially block the iodine your thyroid needs to function.
  • You probably would have to eat an excessive amount for this to happen, though.
  • Kale also lists highly in the US for being contaminated with pesticides, so you should wash it thoroughly before eating it raw.

There’s no doubt that kale is an excellent health food. Just one cup can give you more than 200% of your vitamin A for the day, and nearly 700% of your vitamin K. It also contains certain plant compounds that can help protect against certain cancers.

But in some cases, eating kale might not be as healthy as you think. For example, it can interact with thyroid function if it’s eaten in very high amounts. It contains something called progoitrin, which can interfere with thyroid hormone synthesis and essentially block the iodine your thyroid needs to function. This can result in fluctuating blood sugar levels and weight.

However, it’s probably not something to worry about as you would have to eat an excessive amount of raw kale to experience these negative effects – a lot more then you’re likely to have in one sitting. If you’re unsure, or you have an underactive thyroid (hypothyroidism) already, ask your doctor or a dietitian.

Read more: Bubble tea is a whole lot worse for you than regular tea. Here’s why.

If you regularly eat kale, it might also be a good idea to make sure you wash it thoroughly. The Environmental Working Group just released its “Dirty Dozen” list for the year, which is a guide to the products that are covered in the most pesticides.

It found that kale had the highest pesticide residues compared to nearly all other produce found on supermarket shelves in the US.

About 60% of the kale samples tested positive for Dacthal, which is listed as a Group C human carcinogen according to the National Library of Medicine – meaning there is suggestive evidence of carcinogenic potential but more research is needed.

“We were surprised kale had so many pesticides on it, but the test results were unequivocal,” said EWG toxicologist Alexis Temkin. “Fruits and vegetables are an important part of everyone’s diet, and when it comes to some conventionally grown produce items, such as kale, choosing organic may be a better option.”

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