Medical Examiner

More Studies Like the Red Meat Flip-Flop Are Coming

Nutrition researchers are battling methodologists. What does it mean for what you’re supposed to eat?

Meat!
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You used to want to eat less red meat. But now, eating red meat, in whatever amount you eat it, is just fine. You’ve surely seen the headlines suggesting as much. A team of scientists gathered up all the papers on the health effects of red meat and published a series of analyses evaluating what they said. Which is: The benefits of cutting down on red meat consumption (the recommendation was to cut by three servings a week) are very small, if those benefits even exist at all. In the New York Times, Gina Kolata dubbed it a “remarkable turnabout” from the standard advice to watch your hamburger intake.

This isn’t as remarkable as it might sound, because this turnabout isn’t about new evidence. It’s about how the evidence is being interpreted, and the limits inherent to nutrition advice in the first place.

Most of the authors of the new papers are not nutrition researchers. They’re methodologists and other medical experts with a bone to pick about how nutrition research is done. Last December, many from the group published a paper, an objectively dry document that is at the root of all this havoc, in a journal on research methods,. Nutrition advice, they wrote, is, by the standards of any other medical advice, quite sloppy. It places “excessive trust” in observational studies, wherein researchers try to make sense of piles of wildly varied and questionably accurate diet logs, rather than prescribing participants strict, controlled food regimens. This team proposed applying the same rubric applied to drug trials to nutrition research, with the goal of giving clinicians—who, just like us, can have a hard time sorting through wildly variable results—an easy bottom-line recommendation to give to patients. And so, the papers represent “a new way of judging nutrition research that’s going to continue to lead us to uncomfortable conclusions,” Vox writer Julia Belluz wrote in a tweet. (She has a very helpful story breaking down the red meat news.)

Red meat researchers really hate all this. It sent folks at Harvard in particular into a tizzy of damage control, with experts posting a rebuttal on the institution’s website and the chair of the school’s Department of Nutrition, Frank Hu, giving interview after interview to the media, including to me. “Several meta-analyses found that eating too much red meat is bad for you,” is how he sees it. For example, one analysis found that if everyone cut red meat intake by three servings per week, for every thousand people, about seven fewer might die from cancer … maybe. One feature of the new analysis is that the authors say those benefits are shaky and, even on a population level, not guaranteed to exist. Still: That’s not zero. For Hu, it is enough. He thinks it’s inappropriate to apply the standards of drug trials or more rigorous science to nutrition; he also published an observational study concluding that red meat is bad for you just this summer. He is deeply invested in that line of thinking not being overturned.

Another thing that clarified Hu’s thinking for me is a line from the Q&A on Harvard’s website that he and other experts authored: “These guidelines are inconsistent with the principle of ‘first do no harm.’ ” They give an example of someone who eats two servings of red meat per day (a lot, compared with the average American) and note that it would be irresponsible to not advise this person to cut down. Based on the tiny benefits that accrue from eating three fewer servings per week, such a person could possibly up his odds of being felled by something other than cancer a few times over. (Note that cutting down on red meat, even in the best interpretation, guarantees nothing for any one person.) “If you find something bad, you don’t want people to continue their habits,” says Hu. “Even if the evidence is not so certain.”

There’s also the possibility that more rigorous studies, in which humans are prescribed carefully controlled diets the way it’s possible to control the intake of a pill, would turn up a larger warning sign against red meat. But nutrition science isn’t sloppy because nutrition researchers are idiots. It’s sloppy because it’s hard and ethically tricky to get a large population of test subjects to behave in a consistent way, particularly around what they eat. Dennis Bier, who was not involved in the work, told the New York Times that “the rules of scientific proof are the same for physics as for nutrition.” That’s both true, and laughable. Humans can’t be studied the way particles and solar systems can. A statement like “bacon is bad for you” can never have the same weight as the laws of gravity. Nutrition researchers may find ways to make their field more rigorous, or they might just continue to disagree with the people who are critiquing their field. In the meantime, the best we can do is understand the parameters of the evidence that we do have. While the precise downsides of bacon, for example, are unclear and possibly nonexistent, what is apparent is that we don’t really have enough evidence to consider it a bad food.

But didn’t you, prior to this week, think that bacon was pretty bad? Perhaps the most important flaw of nutrition research isn’t how it’s done but how it’s disseminated into our lives: in blared headlines, in diet books, in health food trends, into a culture that already demonizes (and glorifies) food. Nutrition science is an imperfect tool that uncovers very slight effects across a big population and then delivers the results urgently to you, an individual who may or may not benefit from following along. It doesn’t always take into account what else you eat, or whether eating bacon makes you feel crappy or wonderful, or if you want an excuse to eat more kinds of protein, or if you care about cutting down on meat for the sake of the planet. If anything, take this week as permission to think more about how foods fit into your own life. That research protocol will surely be applied to more foods. We’re going to have more food news cycles like this one.

Correction, Oct. 4, 2019: The original subhed for this piece incorrectly referred to “nutritionists” when it should have referred to “nutrition researchers.”