By most measures, kale and red meat are as different as two foods can be. It's not just the animal-vegetable thing: Kale is trendy, high on celebrity-chef lists of healthy foods (http://tiny.cc/…), but still rarely seen on most American dinner tables. More Americans consume red meat but hardly anyone outside the red-meat industry considers it a health food. Even for some of its fans, it's a guilty pleasure.
Suddenly, though, these two representatives of opposite ends of the food spectrum share something in common: unwanted attention on the health front. The World Health Organization is on the verge of declaring red meat a possible or even probable cause of cancer (http://tiny.cc/…). Somewhat more surprisingly, kale has come under fire for alleged links to maladies ranging from hair loss to heart arrhythmias (http://tiny.cc/…).
Nutritionists have been beating up on red meat for a long time, mostly as a factor in heart disease. Some also worried about cancer, although until recently that link was deemed less well grounded (http://tiny.cc/…) (http://tiny.cc/…). And while the industry disputes these links -- and will redouble its objections when the WHO weighs in -- red meat consumption continues to decline (http://tiny.cc/…).
For kale, health concerns are a new experience. Little research has been done, and the recent work by a qualm-raising California biologist seems shaky, the website Vox argues (http://tiny.cc/… -- but if you click on this, be sure to read the correction at the end of the piece). It's hard to trust a researcher who, among other things, goes shopping for a new laboratory when the first doesn't give him the results he's looking for.
Other researchers have established that kale is a "hyper-accumulator" of thallium, a toxic metal. The California biologist tried to establish a link between thallium and arrhythmia but questions about his work abound. Assume for the sake of argument, though, that a link had been established. A critical question would still need to be answered: How much kale can a person eat safely?
"How much" is the question that is too seldom asked when the safety of food is called into question. Someone does a study showing very high levels of X increase the risk of disease Y in animals. The public panics, even though studies of human populations provide no reason for alarm.
The American Cancer Society says that's exactly what happened in the scare over the artificial sweetener aspartame (http://tiny.cc/…). Two somewhat controversial studies linked very high doses of aspartame to increased cancers in rats. Meanwhile, "Most studies in people have not found that aspartame use is linked to an increased risk of cancer." But the consumer backlash "crushed sales" (http://tiny.cc/…) and now aspartame is coming out of Diet Pepsi. The customer is always right, even when he's wrong.
In the case of kale, a researcher in Italy told Vox a person would have to eat several kilograms a day, every day, to get sick. The researcher said it's "close to impossible" for humans to be poisoned by kale unless it's grown on the equivalent of a Superfund site.
The cancer case against red meat doesn't rely on animal experiments -- it's supported by statistical studies of human populations (http://tiny.cc/…). But whatever the WHO ends up deciding, the "how much" question will remain pertinent. The American Cancer Society urges Americans to "eat less red and processed meat" but doesn't say how much less.
Short of proof that no safe level of red meat exists, a sudden mass defection from hamburger to kale seems improbable. And without much more and better evidence about thallium than now exists, kale sales are not likely to plummet.
We need scientists to study the effects of what we eat. We also need more context and perspective in the reports of their findings. Sensationalism sells, which is why so many scientists, scientific-journal editors and journalists reach for the scare headline and minimize the doubts, caveats and limitations in reporting research results.
But the drumbeat of "this can cause cancer" and "that can cause diabetes" numbs many people into skepticism and apathy. Because the information they get doesn't distinguish between more serious health risks and dangers that are only dangerous when consumption is in excess, they make less intelligent decisions.
For scientists, calculating how much of something will endanger health is harder than determining that at some quantity a hazard exists. But that's where the real benefit to public health lurks -- in answering the question, "How much?"
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