The Notion of ‘Toxic Kale’ Has Gone Viral. But Is it True?

“Toxic kale” is making news because of anecdotal evidence by one molecular scientist in one magazine article. Experts weigh in as to if we should listen. (Photo: Getty Images)

Over the past decade, kale has undoubtedly become one of America’s favorite superfoods. From salads to chips to juices, kale is frequently found in our favorite uber-healthy staples. It’s low in calories and high in vital nutrients like vitamin K, calcium, magnesium and potassium. Seriously, what’s not to love?

Well, according to emerging science highlighted in an article for Craftsmanship, the answer is heavy metals, notably thallium. Writer Todd Oppenheimer profiles a molecular biologist and alternative-medicine doctor who thinks he’s discovered something very problematic about consumption of kale and other cruciferous vegetables.

The doctor, Ernie Hubbard, mostly sees patients that would put plenty of us to shame. “Health fanatics.” They don’t drink to excess, don’t smoke or do drugs, they exercise frequently, and they eat far better than the average American consumer. And yet, they struggle with chronic issues like fatigue, arrhythmias, neurological disorders, brain fog, digestive issues and skin problems.

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Hubbard, a molecular biologist, was asked to research the underlying cause of his patients’ issues using a Cleveland company’s new detoxification regime called ZNatural. Lo and behold, his patients seemed to make dramatic turnarounds during their programs — but they were also testing high for a couple heavy metals, particularly thallium and cesium.

(Photo: Getty Images)

Huh, thought Hubbard at first. By the third or fourth set of high test results, he was convinced it wasn’t a fluke. With a little digging, he located research to back up what he was seeing in the lab: a peer-reviewed Czech study from 2006 revealing that cruciferous veggies, of which kale is the superstar, seem to be “hyperaccumulators” of thallium.

And that’s not the only research. As Mother Jones points out, a 2013 study from China indicates green cabbage also leaches thallium from its surrounding soil — it’s so stellar at this, in fact, that 2015 Chinese research shows green cabbage can actually be used to purify soil of toxic materials.

In small amounts, heavy metals are important to biological functioning. But in larger amounts, they can have a poisonous effect, causing a variety of symptoms in different severities. For thallium, these include some of the issues observed in Hubbard’s patients, including abdominal pain, vomiting, hair loss, confusion, optic issues, even coma.

Now, this story about a very hazardous health food is picking up steam. But should you be worried if kale is your go-to? Here are some things to remember.

Remember, It’s the Soil

Dietitian Keri Gans, RD, author of The Small Change Diet, says it’s important to remember that, in the research that exists, kale itself is not the culprit containing heavy metals. “You cannot assume because you’re eating kale or other dark, leafy greens that you’re taking in thallium,” she tells Yahoo Health. “It’s the soil that they’re finding the heavy metals in, it’s not existing in the kale itself.”

Exactly how those metals are getting into soil? It’s still anyone’s guess, and very likely differs significantly based on where the kale is being grown. According to Oppenheimer’s report, which centers around Marin County, California, it might be coming from “nearby cement plants, oil drilling, smelting, and, most of all, in the ash that results from coal burning.”

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And when you consume kale and other cruciferous, you have to remember what you’re getting in nutritional returns — and that’s “vitamins K, A and C, calcium, potassium and folate,” says Gans. Dark, leafy greens are also staples in popular healthy regimens like the Med and DASH, and are becoming a go-to for diets aiming at long-term brain health. So…

Let’s Not Vilify Kale

First off, there’s not a ton of existing research out there right now on cruciferous veggies and heavy metals, let alone kale and heavy metals. “Toxic kale” is making news because of anecdotal evidence by one molecular scientist in one magazine article — even if Hubbard’s insights may be worth noting for further research, says physician-nutrition specialist Jennifer Warren, MD, Medical Director at Physicians Healthy Weight Center

“[Hubbard’s] clinical ‘guesses’ and non-scientific observations do not qualify as a reason to panic,” Warren tells Yahoo Health. “Has he stumbled across a real, previously unidentified problem? Perhaps. But this has not been demonstrated in any clear, scientific way at this point, so I would not advise changing anyone’s diet based on a wild guess, or preliminary observation. Jumping to conclusions is never a good idea.”

Conclusions that kale, in particular, is the villain are particularly far-fetched. It may be that kale is just the news peg for this story, since we now live in a health-conscious culture serving up this buzzy superfood in so many forms — from kale chips for a snack, to kale in our morning green juice, to sautéed kale for dinner.

Kale is not the only potential veggie that may take in heavy metals like thallium, though. Preliminary research shows it might be leaching into other leafy greens, too. Think: bok choy, spinach, cabbage, mustard or collard greens — which, even still, doesn’t mean you’re getting it in your greens.

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Case-in-point: a 2001 study in the Journal of Plant Nutrition, thallium has been found in many members of the Brassica family, like peas, spinach and green beans, and in highest levels in watercress, radish, turnip and green cabbage. Kale? Not mentioned in the research. So, let’s not be so quick to hate on kale.

Kale has also been accused of causing conditions like hypothyroidism and kidney stones, issue that are also not clear-cut. Although you may be asked to watch your kale and leafy green consumption if diagnosed with hypothyroidism, Warren points to the advice of Harvard endocrinologist Jeffrey Garber, MD, the past time kale hit the news for this issue.

It’s true that the metabolic effects of eating kale and leafy greens may ultimately mess with the thyroid’s hormone synthesis and the prevent uptake of iodine. But when asked about an emerging kale-and-hypothyroidism controversy after writer Jennifer Berman’s op/ed piece in the New York Times in 2014, his thoughts were simple: “I think it’s overplayed.”

Garber says it is “theoretically” possible that eating kale could lead to the condition, “but it would be unusual.” As long as you’re not eating a massive amount of the veggie, or living in a country where iodine deficiency is prevalent, you’re more than likely going to be fine.

“As for the controversy with kidney stones and kale, that is an oversimplified issue,” Warren says. “In reality there are different types of kidney stones, with different causes.”

In the past, people with histories of kidney stones were told to limit their calcium intake, and leafy greens are big sources. However, Warren says science is now showing it’s actually best to just stay within the recommended daily amount of calcium to ward off kidney-stone recurrence, not severely restrict the mineral in your diet.

So, a little kale? You should be fine. But again, a whole lot of kale? Now that we’re back on the subject, let’s talk about that.

How Much Kale Are You Actually Eating?

The amount of kale and other dark, leafy greens a person consumes is also a major question. And how much might possibly be enough to lead to symptoms? Well, maybe a lot. Much more than most will probably be noshing on.

One woman in the Oppenheimer piece admits to being in “ridiculously great shape,” but also ridiculously obsessed with kale and green cabbage. “I joke with my clients that I’m the cabbage queen,” she says.

Not only could this over-consumption of kale and cabbage be the reason for super-high thallium levels, it’s also not a great idea to zero in on one food and get into “overkill mode.” Despite cruciferous veggies’ benefits, says Gans, this sort of hyper-healthy eating could lead to disordered eating or orthorexia, a condition where a person obsesses about eating certain foods deemed ultra-nutritious.

There really is such a thing as too much — in more ways than one. All dietary decisions should always factor into maintaining overall health. For instance, eating too many of these dark, leafy superfoods can also lead to an excess of vitamin K in the body. On its own, vitamin K is an essential nutrient for regulating blood-clotting — but too much can thwart that process, says Bonnie Taub-Dix, RD, owner of Better Than Dieting.

“With lots of kale and other dark, leafy greens, I always worry about blood-clotting in my patients,” she tells Yahoo Health. “Especially with people who may already be on blood-thinning medications, or may be taking supplements with extra vitamin K, like those containing gingko biloba or vitamin E.”

Taub-Dix says she sees so many patients with the “some is good, more is better” mentality, which is a poor approach. “People don’t realize that food has powerful properties,” she explains. “If you’re eating a lot of these leafy greens with vitamin K, and also have it in your supplements, I’d worry about bleeding if you cut yourself, or it may be a problem if you’re planning a surgery.” Always talk to a doctor about all medications and supplements you are taking.

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According to Gans, the lesson here is one she instills in her patients anyway: diversify your diet. “You always want to eat a variety of foods,” she says. “The more variety you have, the more nutrients you’re getting. You can’t demonize one food, and you can’t live on one food. All food groups are important, and if you’re OD-ing on one, you’re probably not getting enough of another.”

So, eat smart and eat with variety. Keep kale and other cruciferous veggies on your radar as more research comes in – but don’t nix them from your regimen, says Gans. If you’re concerned about the effects of any food, talk to your doc.

Ultimately, though? “The benefits of eating dark, leafy greens far outweigh the assumption that you will wind up consuming thallium,” Gans says, explaining that this speculative worry is far from certain.

Gans says three to five servings per day of veggies is the recommended dose. Mix it up, and and you should stay in good shape – and for most, this superfood is probably still a super food for delivering key nutrients.