Last week a new study came out that questioned the long-standing recommendation to eat less red meat.Maybe you’re confused, or maybe you’re just rolling your eyes at yet another round of contradicting ideas about what good nutrition looks like. Both reactions are warranted. Dozens of nutrition scientists are up in arms about the study’s conclusion, while others argue that it does a public good to illustrate the shaky and inconclusive nature of the science behind dietary guidelines.Here’s what you need to know about what that study actually found and whether or not you should worry about it.
Old Research Can Support New Ideas
published in Annals of Internal Medicine on October 1 concluded that the current public-health recommendation to eat less red and processed meat isn’t backed by strong evidence, and it went on to make new recommendations: that adults 18 years or older do not need to monitor or limit their consumption of red meat or processed meat.
The article included five papers, each a systematic review or meta-analysis of past studies. So the researchers (there were nearly 20 of them, from institutions across the globe) didn’t collect new data, they just analyzed the data that already exists. These types of papers—in which researchers use existing data instead of collecting their own—are very common, especially in nutrition. (A controversial study that came out earlier this year, claiming that eggs are bad for you, was also a meta-analysis.) “What these researchers did is use an evaluation tool to look at the strength of the data on the association between red-meat consumption and mortality and disease risk,” says , nutrition professor emeritus at the University of Illinois. And they concluded that the existing evidence is very weak.
Unsurprisingly, a lot of nutrition experts weren’t thrilled at this attack on current dietary guidelines. A statement issued by Harvard’s T.H. Chan School of Public Health argued: “The publication of these studies and the meat guidelines in a major medical journal is unfortunate because following the new guidelines may potentially harm individuals’ health, public health, and planetary health.” The post went on to point out that this study’s analysis of 70 previous cohort studies, including a total of over six million participants, did show an association between red-meat consumption and chronic disease risk. The thing is, no one is arguing that this association doesn’t exist—simply that this association might not mean what we think it does.
Correlation Is Not Causation
Large cohort studies use what’s called a risk ratio, to evaluate how much your behavior influences your likelihood to experience a certain negative outcome. These studies have found a positive correlation between red-meat consumption and disease risk—but it’s small. “The risk ratio for smoking and lung cancer is a 12, for example, and the risk ratio for red meat and heart disease is about one and two-tenths,” Layman says.
Although this ratio isn’t huge, it still warrants more in-depth studies. “Large cohort studies can’t prove cause and effect, they can just generate hypotheses,” Layman says. The problem, he explains, is that follow-up research—randomized control trials (RCTs), clinical trials, experimental animal trials, and more—hasn’t been able to prove the red-meat hypothesis. So while we know that red meat and cancer risk are correlated, no study has been able to prove causation.
Proving Causation Is Almost Impossible
While RCTs—which include a control group to measure against—can show cause and effect, it’s really hard to design a proper nutrition study this way. “If you have someone eat less red meat, they will invariably replace it with something else,” says Brian St. Pierre, a registered dietitian and director of performance nutrition at . So how do you know whether their eventual outcome is due to eating less meat or due to whatever foods they used to replace meat? Plus, with dietary intervention, there’s no way to control for the placebo effect. For these reasons, RCTs are relatively rare in nutrition research, which is why we rely so much on observational studies.
Population Health Is Not Individual Health
One of the arguments against the new study is that, even though the evidence for causation isn’t there yet, the association between red-meat consumption and disease risk at the population level is well proven and still relevant. For example, the existing body of research shows that lowering red-meat consumption by three servings a week could lead to six fewer heart attacks per 1,000 people. And sure, that does seem relevant when you’re thinking about public health. But, Layman asks, “What does that really mean in an individual’s life? It’s hard to say. Does that add six days to your life? Six months? Six years?” We don’t know.
Why even have dietary guidelines then? Because people are looking for advice. “NASA waited until we had a good understanding of the science before sending a man to the moon,” Layman says.“Unfortunately, with nutrition, people can’t wait. They’re eating today.” But his advice is to mostly ignore the nitty-gritty of dietary guidelines and nutrition research. “Eat a variety of foods, and don’t eat too many calories,” he says. “That’s by far the healthiest thing you can do.”
St. Pierre agrees, saying that when you look at the full body of nutrition research, it’s clear that there are many different ways to eat healthy. “The first step for most is to begin to eat more whole, minimally processed foods—both plant and animal-based—and fewer ultraprocessed foods.”
Don’t Overthink It
The biggest issue with dietary guidelines isn’t what they have to say about one specific food—it’s the fact that most people don’t follow them anyway.Only about eat the recommended five servings of fruits and vegetables a day. The most state that most people eat more than the recommended amount of grains, protein, added sugars, saturated fats, and sodium.
This study and similar reviews are useful not because of how they directly influence how individual people eat but because of how they impact nutrition science and guidelines. “I think this group did a great service by highlighting how weak the narrative is that’s out there about red meat, that it’s not strong science,” Layman says.
Still, it’s unclear what the study means for the future of nutrition research. “Our current base of evidence on specific foods is not overly strong, but the researchers seem to be missing the point: that to conduct the research to truly answer these questions would be ridiculously resource intensive. And incredibly unlikely,” St. Pierre says.
Should all of this change the way you look at red meat? Probably not. Instead, it should encourage you to focus less on following specific guidelines and more on eating a variety of foods that make you feel good.