I have an unimpassioned relationship with kale. I'll eat it. Sometimes, I'll even enjoy it (I'm looking at you, kale salad at Chef Jonathan Waxman's Barbuto in Manhattan's West Village). But unlike many of my fellow foodies, I don't fawn over the leaves of green.
In the last day or so, I've seen apoplectic friends on social media sharing a story that warns your kale may be killing you. The original source of this hysteria stems from Todd Oppenheimer's narrative, "The Vegetable Detective." Oppenheimer details the journey of a California biologist and alternative-medicine practitioner who began noticing a relationship between vague, but persistent, symptoms (including chronic fatigue, hair loss, and neurological problems) in his patients and one of their favorite foods: kale.
The biologist in Oppenheimer's story, Ernie Hubbard, ran chemical analyses on urine samples from people experiencing these vague symptoms. He found that several of them had higher than normal levels of thallium, a heavy metal that is particularly poisonous at high doses (higher than folks can get from their food, we might add). When he quizzed these patients on what they were eating, they all pointed back to the crucifer.
Kale, and most leafy greens, naturally absorb minerals and chemicals from the soil in which they are grown. Among those chemicals can be--and often are--heavy metals and pollutants we obviously would prefer stayed as far away from our plates as possible. But the levels of thallium Hubbard found were just too high and present in too many people to be a coincidence.
Thinking he would find a relationship between fertilizers or farming chemicals and the high levels of the heavy metal, Hubbard tested both organic and conventionally grown kale. Surprisingly, it turns out there was more thallium in the organic varieties he tested. How is that? Well, Hubbard and Oppenheimer don't really have a conclusion. Maybe it's the water. Maybe it's the fertilizer. Maybe, as the original story suggest, it's a perfect storm of a lot of issues compounding a problem that leaves our kale with levels of thallium that are just higher than we'd like.
So now what? Do you have to give up kale? Well, no. Here's our takeaway from this story: Don't panic. Can you have too much of a good thing? Absolutely. Nutrient toxicity is a real, but exceptionally rare, thing. Is your daily kale smoothie going to leave you suffering mysterious symptoms? Probably not. Plus, Hubbard's research lacks a little to be desired. He conducted most of these studies from his home. An accredited, peer-reviewed scientific analysis his research was not.
But if you lean heavily on kale or any other single vegetable or fruit for the majority of your nutrients, you might want to rethink your food plan. You may be getting a lot of the same nutrient over and over again every day. You need a balance so your chances of building up toxic levels of micronutrients and chemicals remains low. And, with the popularity of juicing, it might actually be easier for you to get concentrated amounts of certain minerals and vitamins at levels that are not necessarily healthy or useful. So vary your plate. Eat a variety of fruits and vegetables, and you probably can keep eating your kale. If that's your thing. But spinach is great too, you know.