Oh, how Superfood Kale seems to have fallen. Once mightier than Popeye’s spinach, now it’s accused of acting more like Superman’s kryptonite. Peruse the Web and social media these days, and you may bump into kale bashers, kale haters, kale doomsayers, even kale paranoiacs and see headlines like these collected recently by the media watchdog group Health News Review…

“People Are Getting Seriously Sick From Eating Kale: Find Out Why This Superfood Is Actually Super-Poisoning”

“Could Kale be Poisoning You?”

“Is Kale Making People Sick?: The Dark Side of Everyone’s Favorite Superfood”

“The Shocking (and Scary) Truth About Kale”

You know that kale is packed with a stunning amount of nutrients. But could you be poisoned by America’s favorite superfood? We investigated.


Headlines like those above have their origins in an article in Craftsmanship magazine, later amplified in a Mother Jones magazine article entitled “Sorry, Foodies: We’re About to Ruin Kale.” The story: A molecular biologist who works at an integrative health clinic in California theorized that high levels of the heavy metal thallium from soil were seeping into kale—and may be causing a variety of ailments including chronic fatigue, hair and skin problems, cardiac arrhythmias, neurological problems and “foggy thinking.”

The “kale-is-making-us-sick” hypothesis, however, is based on shaky information—anecdotal statements from people with various symptoms who said they liked to eat kale, and the results from a single lab that said it found high levels of thallium in kale samples. (That lab has been the subject of controversy and lawsuits over faulty testing, so at a minimum one would want to see its results replicated at other labs.) Nor has there been any evidence published in a peer-reviewed scientific journal that links kale intake with any disease or symptoms.

Here’s what’s known: Thallium is poisonous, and kale can accumulate thallium from soil. So can many other cruciferous vegetables such as broccoli, Brussels sprouts, cauliflower and cabbage…as well as canola, the plant used to make cooking oil. But most thallium is found very deep in the earth’s crust, far below the soil level, so it’s not likely to get anywhere near the kale plant’s roots. As one molecular biologist interviewed by a reporter for VOX magazine put it, “It is close to impossible for humans to be poisoned by eating kale from normal soil.” The exception is soil that is very near coal-burning power plants, since coal ash can contain high levels of thallium, or soil that is contaminated with industrial wastes. (Thallium is used in manufacturing electronic devices and semiconductors.)

So…unless your kale is grown on property that has been contaminated by nearby industrial activity, you’re probably just fine. The real issue is contaminated soil, and that affects all of agriculture, not just one food. If any real evidence about kale or cabbage or any other food does show up to the contrary, we’ll be sure to let you know.

In the meantime, though, there actually are some evidence-based reasons that some people may want to steer clear of kale—and why all of us should be wary of eating excessive amounts of this increasingly popular green.


As the kale scare blows over, we do want you to know about a few ways to enjoy this nutritious vegetable in the safest, healthiest way. A few tips…

• Rinse it. Good advice for all fruits and vegetables, but particularly important for leafy greens with lots of crevices, like kale. The concern is dust. For instance, lead from automobile emissions and old paint chips is found in dirt. Although it’s not easily absorbed by plants, lead-containing dust formed by the soil lands on the leafy greens and settles in the crevices. The solution—a good rinse under running water. Don’t use soap or detergent.

• If you have a thyroid condition, such as hypothyroidism (low thyroid hormone levels), don’t overdo raw kale (or other cruciferous vegetables)…as in juicing. It contains compounds that may affect the thyroid in people with this condition. That’s not a concern for people with normal thyroid function, and even if you have hypothyroidism, cooked kale a few times a week is fine. Cooking destroys most of these compounds.

• If you’re on a blood thinner, talk to your doctor about foods such as kale that are rich in vitamin K, which helps blood clot. For the medications to work right, you need a consistent amount of vitamin K in your diet, so you may be told to limit or avoid foods such as kale.

• Try a little variety—and moderation. These are hoary nutrition principles, but they’re wise. Go on any food jag too long, and you may create imbalances in your diet. Eat a variety of foods, including a variety of green vegetables, and you’ll get a wider array of nutrients…and if there are contaminants in a particular food, you won’t be exposed to large amounts.


Remember kale is a good source of calcium as well as vitamin K…both good for bones. Plus, kale, unlike, say, spinach or beet greens, is low in oxalates, which can interfere with calcium absorption and may contribute to kidney stones. Kale is also a good source of iron, potassium and fiber, and it has very few calories. Like other cruciferous vegetables, it contains compounds that help the body clear toxins from the liver—and it has anticancer properties.

Finally, remember that the only green that matters is the green that you actually eat. We’re still enthralled with the crunchy pleasures of a well-composed kale salad with toasted nuts, an olive-oil/lemon vinaigrette and a few shavings of Parmigiano-Reggiano. But we also like broccoli, spinach, bok choy, collard greens, Swiss chard, watercress, mustard greens, red cabbage, napa cabbage…