Most major dietary guidelines—including those in the United Kingdom, the United States, and those published by the World Cancer Research Fund—recommend that people reduce their consumption of red and processed meats, which research links to health problems like cardiovascular disease and cancer. But new work from an international group of scientists who analyzed existing research on the effect of meat on individual health says that those guidelines aren’t based on good evidence.
The group also issued what they called a “weak recommendation” with “low-certainty evidence” that adults stick with the amount of meat they usually eat.
“There’s nothing there on the direct effects of red meat, really,” says Chris D’Adamo, director of research for the University of Maryland Center for Integrative Medicine, who was not involved in the research.
The analysis, which included five individual studies published in the Annals of Internal Medicine, was published Monday evening and quickly criticized by experts and medical groups. They took issue with both the methodology behind their conclusions, which only considered a small sliver of nutrition studies, as well as the lack of consideration of the environmental impact of meat. They were also concerned about the impact this would have on public perception of nutrition research.
The group conducting the studies, called NutriRECS, incorporated data from around 100 large nutrition studies, which included hundreds of thousands of patients. They did find that eating red and processed meats makes small contributions to overall risk of cardiovascular disease, cancer, and death. However, the NutriRECS researchers determined that the quality of the evidence in the studies they looked at was low, so the small risk should not be used to suggest that people reduce their meat consumption.
Much of the controversy around this particular set of studies, and nutrition research in general, centers on the types of evidence that researchers think are strong enough to support diet recommendations. The team evaluated the evidence around red meat using a framework called GRADE, which ranks studies that observe people (rather than establish groups that are given specific interventions), and is deemed low-quality. Many nutrition studies are observational because it’s challenging to closely control people’s diets for the decades it takes to figure out how the food they eat impacts their health, says Christopher Gardner, a professor at the Stanford Prevention Research Center.
They are deemed low quality for good reason: They rely on people telling researchers what they ate, and humans are often bad at remembering (and sometimes lie). They’re not ideal, Gardner says, but they do offer enough information to guide general recommendations.
“I understand the frustration that nutrition research is hard,” Gardner says. But only considering a small subset of studies and using that to counteract major public health bodies contributes to mistrust in science, he says. “Public health officials come at this from many different sides, and appreciate the complexity. They make recommendations saying that it’s not perfect, but here is our advice.”
An editorial accompanying the NutriRECS studies argues that they point to the problems with observational research, and writes that nutrition might be better off moving away from them and investing energy into conducting those hard-to-do clinical trials. D’Adamo says he agrees. “We need more clinical studies,” he says. “Observational studies can be useful, but they have been misleading.”
The new studies also only consider the direct impact of eating meat on someone’s body, which is not the only way meat can affect health: Meat production, particularly beef production, is a major contributor to greenhouse gas emissions and global climate change. Emissions and the changing climate are, in turn, major public health threats. So even if eating meat won’t directly cause heart disease in an individual, breathing in air polluted by meat production can. That’s critical to consider when making dietary recommendations, Gardner says.
Environmental impact is important, D’Adamo says, though it’s hard to incorporate directly into the analysis of individual health impacts. “Meat is certainly contributing to things like greenhouse gasses, and there are potentially indirect health effects.” Even if they’re not directly examined in a study, they should be discussed as part of the messaging around findings, he says.
Studies that claim to pull the rug out from established recommendations also create more confusion around nutrition, which is one of the major concerns with the research and the conversation around it. “I can’t think of anything better designed to confuse the public and promote further distrust of nutrition science and science in general,” wrote Marion Nestle, Paulette Goddard Professor of Nutrition, Food Studies, and Public Health, emerita, at New York University. Dietary advice is confusing, she said, and moving goalposts may make people likely to disregard all advice and not worry about any best practices.
Some of the confusion comes from the focus on individual food types—meat, eggs, and so on—which makes nutrition seem like more of a moving target than it actually tends to be, D’Adamo says. Overall, most experts agree. “When we single out a single part of the diet as the sole problem, which has been done with red meat, and other things, we miss the broader picture. It comes down to eating more whole foods, and minimizing processed foods.”