On July 11 at the Point Reyes Farmers Market, I had the delightful opportunity to demonstrate how to make a delicious kale-basil pesto, and the recipe appeared in last week’s Point Reyes Light. We learned about the amazing health benefits of kale and brainstormed how to eat more of these nutritious greens.
The following Wednesday, I received Tom Philpott’s article in Mother Jones entitled “Sorry, Foodies: We’re About to Ruin Kale” in my inbox. I read on with curiosity and bated breath.
Philpott outlines a hypothesis, proposed by Marin-based alternative medicine researcher Ernie Hubbard, that eating too much kale can lead to thallium toxicity. The federal Environmental Protection Agency considers thallium—a heavy metal harvested from ore for electronics, glass and pharmaceuticals—a contaminant in drinking water because ingesting too much can cause hair loss or problems with the intestine, kidneys or liver.
Hubbard observed that several patients undergoing detoxification at the Preventive Medical Center of Marin suffered from various ailments, including fatigue, foggy thinking and digestive problems. These patients, who ate a lot of kale, had detectable levels of thallium in their blood, and kale samples sent to the lab also found elevated thallium levels. In what appeared to be the clincher, a 2006 peer-reviewed paper by Czech researchers showed that kale is very good at taking up thallium from the soil. (Subsequent studies showed other cruciferous vegetables to be similarly adept.) Ergo, eating kale can lead to thallium toxicity.
This is quite a suggestive theory, and deserves, as do all theories, to be put to the test.
Looking closely at Hubbard’s research methods raises important questions; after all, the idea that patients with very common afflictions at a preventive medicine practice list kale as a favorite vegetable is, well, not surprising. In a sound rebuttal of the case against kale, in the online magazine Vox last month, journalist Julia Belluz points out one big problem: a link between kale consumption and thallium levels, or kale consumption and poor health, has not been established in the scientific literature. Clearly more research is needed to make a strong case against the vegetable.
What do the scientists who have researched kale say about this theory? Belluz reached Jiri Zbiral, one of the original authors of the Czech paper. He commented that while it is true that kale grown in soil with high levels of thallium will accumulate thallium, they do not always accumulate it in their leaves. One would need to be eating kale grown in contaminated soils in very large quantities on a daily basis to suffer from toxicity. Another researcher surmised it might take pounds of kale a day to approach toxicity.
What do I make of all of this? It is another case for moderation in all things, even kale.
However, I think the more important issue is the quality of our soil. Thallium is found in soil near coal-fired power plants, factories and fracking operations. We should not eat vegetables grown in contaminated soils. Buy your vegetables locally, whenever possible. Talk to the farmers about the health of their soil. Eat organically. Work for the protection of our environment.
Until better science convinces me otherwise, I’ll be eating kale, with gusto.
Anna O’Malley, who lives in Bolinas, is a physician practicing Integrative Family Medicine at the Coastal Health Alliance.