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 are associated with heart disease such as heart disease. and cancer. But new work by an international team of scientists that analyzed existing research into the impact of meat on personal health says that these guidelines are not based on good evidence.
The group also issued what they called a "weak recommendation" with "evidence of low certainty" that adults stuck with the amount of meat they normally eat.
"There is nothing about the immediate effects of red meat, really," says Chris D & # 39; Adamo, research director 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 night and was quickly criticized by experts and medical teams. They questioned both the methodology that led to their conclusions, which examined only a small part of nutrition studies, and the lack of assessment of the environmental impact of the meat. They are also concerned about the impact this would have on public perception of nutrition research.
The study team, called NutriRECS, incorporated data from about 100 large nutrition studies involving hundreds of thousands of patients. They found that eating red and processed meat made little contribution to the overall risk of cardiovascular disease, cancer and death. However, NutriRECS researchers found that the quality of the data in the studies examined was poor, so the low risk should not be used to indicate that people are reducing meat consumption.
Much of the controversy surrounding this particular set of studies, and nutrition research in general, focuses on the types of evidence that researchers believe are strong enough to support dietary recommendations. The team evaluated the data on red meat using a framework called GRADE, which classifies studies that observe people (rather than creating groups receiving specific interventions) and is considered to be of poor quality. Many nutrition studies are observational because it is difficult to closely monitor people's diets for the decades it takes to understand how the foods they eat affect their health, says Christopher Gardner, a professor at the Stanford Prevention Research Center.
They are considered low quality for a serious reason: They rely on people telling researchers what they ate, and people are often bad at remembering (and sometimes lying). They are not ideal, says Gardner, but they do provide enough information to guide general recommendations.
"I understand the frustration that nutrition research is difficult," says Gardner. But just looking at a small subset of studies and using them to offset major public health providers contributes to mistrust in science, he says. "Public health officials come to it from many different angles and appreciate the complexity. They make recommendations saying it is not perfect, but here is our advice."
An accompanying version of the NutriRECS studies argues that they point to problems with observational research and writes that diet can be better than removing them and investing energy in conducting these difficult clinical trials. D & # 39; Adamo says he agrees. "We need more clinical studies," he says. "Observational studies may be useful, but they are misleading."
New studies also look only at the direct impact of eating meat on one's body, which is not the only way meat can affect health: Meat production, particularly beef production, contributes significantly to greenhouse gas emissions and global climate change. Emissions and the changing climate are in turn significant threats to public health. Thus, even if eating meat will not directly cause a person's heart disease, breathing in the air contaminated by meat production can. This is crucial to consider when making dietary recommendations, says Gardner.
The environmental impact is significant, says D & # 39; Adamo, although it is difficult to integrate directly into the health impact analysis. "Meat certainly contributes to things like greenhouse gases and has potential indirect health effects." Even if they are not directly examined in a study, they should be discussed as part of messages about the findings, he says.
Studies claiming to pull the rug out of established recommendations also create more confusion about nutrition, which is one of the main concerns for research and debate around it. "I can't think of anything better designed to confuse the public and promote further distrust in the science of nutrition and science in general," writes Marion Nestle, Professor Paulette Goddard on Nutrition, Food Studies and Public Health emerita at the University of New York. Nutrition tips are confusing, he said, and moving goals can make people overlook all the tips and not worry about best practices.
Some of this confusion comes from focusing on individual types of foods – meat, eggs and so on – which makes the diet look more like a moving target than it really tends to be, says D & # 39; Adamo. Overall, most experts agree. "When we single out one part of the diet as the only problem that has been caused by red meat and other things, we lose the bigger picture. It comes in eating more whole foods and minimizing processed foods. "