Who Shouldn’t Eat Kale?

Kale is lauded as the holiest of greens—it’s hard to find a restaurant that doesn‘t have a kale salad nowadays. And it deserves it. Full of antioxidants, fiber, vitamins, minerals, and even omega 3 fatty acids, it’s one of the more nutritionally dense greens you can toss on your plate.

But kale isn’t necessarily the green savior it’s cracked up to be—or, at least, it’s not for everyone.

WHY KALE ISN’T FOR EVERYONE

There is a growing movement of kale haters out there. Famously, Dave Asprey—the guy behind the Bulletproof Diet (and bulletproof coffee)—thinks most of us should be wary of kale. And he makes some great points. But who really suffers from eating kale? Let’s look into the downsides of this leafy supergreen.

It’s high in oxalates.

Oxalates are a common ‘antinutrient’ that actually binds to vital minerals in the gut, essentially stealing them from your body. It especially loves binding to the calcium in your blood, which can cause crystals of oxalic acid to form.

These crystals are theorized to travel throughout the body and cause inflammation and muscle pain. They may even be behind the development of painful kidney stones. 

But back to its mineral hijacking properties. If you consume a lot of raw kale, the high oxalate content means that you may not be absorbing all the nutrients you should be. In fact, one study suggests consuming rich mineral water when consuming a high oxalate diet. So it might be useful to limit or be aware of your intake of oxalate-dense foods, if you are concerned about mineral deficiencies.

It’s also goitrogenic.

Cruciferous vegetables, like kale, can actually impede the function of the thyroid when over-consumed. This is because they contain goitrogens—yes, as in the compounds that can build up and cause goiters.

Goitrogens actually inhibit the uptake of iodine in the thyroid gland. Without iodine, the thyroid suffers and drastically slows down hormonal production. When your thyroid slows down, crucial bodily functions like your metabolism take a massive hit.

If you already suffer from thyroid dysfunction or have a family history of thyroid issues, it might be best to exert caution around goitrogen-dense foods, like raw kale.

SO, WHO SHOULDN’T EAT KALE?

For some of us, kale isn’t the superfood it’s made out to be. Here’s the lowdown on who shouldn’t eat kale.

If you suspect you have thyroid issues or some form of hormonal imbalance, be conscious of how much raw kale you are eating on a regular basis, due to its oxalate and goitrogen content. (But cooked kale may be okay—more on that below.)

There are other reasons to avoid kale, especially for those with weak digestion. If you have inflammatory digestive issues like colitis and IBS, you may find that kale is too fiber-rich to handle. Kale also contains a hard-to-digest sugar, called raffinose, which can be challenging for humans to digest—we lack the proper enzymes—so it’s up to our gut bacteria to break it down. If you experience lots of bloating and flatulence after eating kale, maybe limit your consumption or switch to a new probiotic.

Of course, if you absolutely love kale, there are options. Steaming and draining your kale before eating drastically reduces the oxalate and goitrogen content, according to research. So, if you love tossing kale in your smoothies, steam a bunch on the weekend, keep it in the fridge, and toss little bits in your smoothies all week long. Easy.

And it may be useful to note that flat-leafed lacinato kale (dinosaur kale) is lower in oxalates than that ubiquitous curly kale.

Kale can be a healthy part of your diet, but it shouldn’t be the only good thing in your diet. Diversity is key when eating produce. Don’t just eat kale all the time, just because it is considered a superfood. For you, it might not be.