FACT CHECK: Did a recent study prove that kale is making people “seriously sick” and everyone should stop eating it?

Claim:  A recent study proved that kale is making people “seriously sick” and everyone should stop eating it.


Examples:   [Collected via e-mail and Twitter, June 2015]

I would like to know if eating too much kale will harm you. Someone posted on Yahoo it can be unhealthy. But how much and is this something to be concerned about as I have a friend who drinks it, eats it incessantly.

Origins:  If ever there was a food people might embrace an excuse to hate with both arms, it’s kale. Depending upon your personal approach, kale might be a bitter cruciferous nightmare foisted upon us by the green gestapo, a food item that arrogantly substitutes itself where “chips” are meant to be, the superfood of choice for tofu-munching and Prius-driving elites, or just hipster lettuce. Kale is perceived as culinary marker of numerous smug stereotypes, and many among us are secretly tempted to ask whether kale is still a nutritional powerhouse when shoved up one’s Crossfit-toned posterior.

In short, for all kale’s selling points (it’s cheap, it’s versatile, it’s high in nutrients and low in things the health conscious tend to avoid on diets), people really want a reason to eschew it for other, less pretentious foods. That opportunity presented itself (not newly) in July 2015, when several articles appeared arguing for the end of kale’s reign.

For example, Inhabitat posited that:

Kale: It’s what’s good for you. Or is it? Kale may be all the rage right now, and you can find it in everything from hipster smoothie bars to crunchy mama play groups. But apparently eating so much kale might not be such great a thing after all.

MotherJones (whose URL described kale as a “silent killer”) similarly chided:

How hipster is kale? For $28, Urban Outfitters will sell you a kale t-shirt. To prep for a big blizzard in early 2015, residents of a trendy Brooklyn section cleaned out the kale bins of their neighborhood Whole Foods. And what would the juicing craze be without it?

Kale is really good at taking up thallium—a toxic heavy metal—from the soil. But today’s kale-fixated juice-heads may doing themselves a disservice.

Perhaps the most accusatory (and most visible) kale hit-piece article was a 16 July 2015 item from the web site Delish titled “People Are Getting Seriously Sick from Eating Kale” subtitled (“Find out why this superfood is actually super-poisoning) that urged readers to “lay off the kale,” bleating:

Kale is heralded for its ample supplies of calcium, magnesium, potassium, Vitamin K, and various healthful phytochemicals and anti-oxidants. But the superfood is hiding a nasty secret: dangerous levels of heavy metals.

In a recent study, molecular biologist Ernie Hubbard found that kale—along with cabbage, broccoli, cauliflower, and collard greens—is a hyper-accumulator of heavy metals like thallium and cesium. What’s more, traces of nickel, lead, cadmium, aluminum, and arsenic are also common in greens, and this contamination affected both organic and standard produce samples.

All of the above-quoted articles cited a single source: a 7 July 2015 article published by Craftmanship magazine (which describes itself as a publication “created to explore the ethos of craftsmanship in its widest sense”). That article, written by Todd Oppenheimer, was certainly well-written and proposed a novel (if entirely anecdotal) idea: What if kale’s benefits were overhyped and it was really a detriment to overall health?

Oppenheimer profiled the work of microbiologist Ernie Hubbard, whom, he explained, has a “background in biochemistry and genetics and “[worked to] explore a range of tests and treatments not often found in traditional doctor’s offices” such as “bio-impedence’ analyzers that measure cellular energy and ‘chelating’ formulas like ZNatural, which aim to stimulate the body to release toxins.'” (Generally, the notion that the body is teeming with “toxins” requiring special cleansing is rejected by medical science.)

The article explained how Hubbard settled upon kale as a possible agent of dietary destruction:

To test this link [to residual thallium levels in kale as a toxin], Hubbard started playing a little game. Whenever the clinic would send him someone with the kind of chronic problems associated with thallium, or any other complaints that were hard to pin down, Hubbard would scribble kale on a little note-card and turn it face-down on his desk. After a short work-up, he’d ask the patient to list his or her favorite vegetables. Over and over, people would mention the crucifers, especially kale. Hubbard would nod, say he expected as much, then show them the note-card on his desk to prove it.

Hubbard specifically described pre-selecting kale alone as the perceived cause of vague and difficult to diagnose symptoms or conditions in the individuals he polled. The portion excerpted above seemed to suggest a suspicion of (and exclusive focus) on kale as the culprit for what Hubbard claims is a self-observed spike in thallium levels in people he tested [PDF]. If any effort was made to examine other foods as thallium sources, it wasn’t mentioned. Fellow cruciferous vegetables are briefly listed, but the article then leapt to the excerpt reproduced above with no further discussion of why “cabbage, broccoli, cauliflower, mustard and collard greens” were eliminated from the list of potentially dangerous salad ingredients.

Moreover, there didn’t seem to be any definitive proof (other than the observations of one molecular biologist) that high thallium levels were a sudden threat, or that the symptoms described by those surveyed were definitively attributed to high thallium (or kale). The article used the word “study,” but it didn’t appear to mean a peer-reviewed or accepted-as-credible-scientific-evidence-finding type of study:

As coincidence would have it, two others in Hubbard’s study were twins, offering two people with the same genetic palate. “So I had a genetics control and an environmental control,” Hubbard says. “I had the kale haters and the kale lovers all getting their urine analyzed, and I think it’s hilarious.”

Another portion of the article pertained to the crops of Tom Willey, an organic farmer in California with whom Hubbard worked in his kale quest. That part of the article highlighted another weakness of the kale theory, explaining that Willey “has never seen thallium in soil tests — then again, he’s never looked for it.” No part of the article pinned down any hard science that evidenced a causal link between kale and adverse health effects, or a spike in thallium levels and a measurable effect on any population. A “2006 study out of the Czech Republic showing how the ‘cruciferous’ family of vegetables behave as ‘hyperaccumulators’ of thallium” is the singular mention of any scientifically indicated link between one idea and the other, but that study involved “cruciferous vegetables” (of which kale is one of many) and their potential to accumulate heavy metals. Even if cruciferous veggies were proved to be heavy metal “hyperaccumulators,” that wouldn’t serve as an indictment of kale alone as an exceptional risk among them.

In 2014, Denver television station KDVR published an article that addressed the putative health risks of kale, but it focused upon a woman with a thyroid condition. A medical expert (Dr. Joshua Klopper of the University Of Colorado Hospital) consulted for that article said kale was not a health risk overall:

Eating raw cruciferous vegetables presents virtually no risk for anyone with a normal thyroid gland. The contribution of kale to exacerbate hypothyroidism is likely minimal in our country where we do not have problems with iodine deficiency. In general, people should be encouraged to eat more fresh fruits and vegetables given the epidemic of obesity and diabetes in our country.

Headlines claiming kale is dangerous are not a new phenomenon. Articles circulating in July 2015 generally stemmed from a single profile in a magazine about craftsmanship, not a medical journal or a new, specific scientific finding. And while research in 2006 identified a possible tendency for all cruciferous vegetables to accumulate heavy metals, that research in no way suggested kale specifically was making people sick. It’s possible further study of kale could reveal such a link, but the suppositions referenced above were based on the untested observations of a single molecular biologist described in an article in a non-medical, non-science-based publication.

Last updated:    17 July 2015

Originally published:     17 July 2015