Most of the major dietary guidelines, including those from the United Kingdom, the United States and the World Cancer Research Fund, recommend that people reduce their consumption of red and processed meats, which is linked to health problems such as diseases. cardiovascular and cancer. But new work by an international group of scientists who have analyzed existing research on the effect of meat on people's health indicates that these guidelines are not based on good evidence.
The group also issued what they called a "weak recommendation" with "unsafe evidence" that adults retain the amount of meat that they usually eat.
"In reality, there is nothing about the direct effects of red meat," says Chris D & # 39; Adamo, director of research at the Center for Integrative Medicine of the University of Maryland, which does not have any effect on red meat. did not participate in the research.
The analysis, which included five individual studies published in the Annals of Internal Medicine, was published late Monday and quickly criticized by experts and medical groups. They challenged the methodology used in their findings, which only took into account a small number of studies on nutrition, 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, has incorporated data from about 100 major nutrition studies, including hundreds of thousands of patients. They found that the consumption of red and processed meats contributed little to the overall risk of cardiovascular disease, cancer and death. However, NutriRECS researchers determined that the quality of evidence in the studies they reviewed was low. Therefore, limited risk should not be used to suggest that people reduce their consumption of meat.
Much of the controversy around this particular set of studies, and nutrition research in general, is about the type of evidence that researchers believe is strong enough to support diet recommendations. The team evaluated the evidence for red meat with the help of a cadre called GRADE, which ranks people's observational studies (rather than creating groups doing the same). 39; object of specific interventions), and is considered of poor quality. Many nutrition studies are observational because it is difficult to closely monitor people's diets for decades to understand the impact of the foods they eat on their health, says Christopher Gardner, professor at the Research Center. on Stanford's prevention.
They are considered of poor quality for a good reason: they rely on people to tell researchers what they have eaten, and humans often have trouble remembering (and sometimes lying). According to Gardner, they are not ideal, but they offer enough information to guide general recommendations.
"I understand the frustration that nutrition research is difficult," says Gardner. But the fact of considering only a small subset of studies and using it to thwart the big public health organizations contributes to mistrust of science, says -he. "Public health officials approach this problem in different ways and appreciate the complexity. They make recommendations saying it's not perfect, but here's our advice. "
An editorial accompanying the NutriRECS studies argues that they highlight the problems of observational and written research that it might be best to distance oneself from nutrition and invest in it. 39 energy in the conduct of clinical trials difficult to achieve. Adamo says he agrees. "We need more clinical studies," he says. "Observational studies may be useful, but they have been misleading."
New studies also only consider the direct impact of meat consumption on a person's body, which is not the only way by which meat can affect health: The production meat, especially beef, contributes significantly to greenhouse gas emissions and global climate change. Emissions and climate change are, in turn, major threats to public health. Thus, even if eating meat will not directly cause heart disease in an individual, breathing air polluted by meat production can. Dietary recommendations are essential when making dietary recommendations, says Gardner.
Dr. D'Adamo says the impact on the environment is important, although it is difficult to integrate directly into the analysis of individual health impacts. "Meat certainly contributes to problems such as greenhouse gases, and can have indirect health effects." Even if they are not directly examined in a study, they should be discussed as part of the message regarding the results, he says.
Studies that claim to break the established guidelines also create more confusion around nutrition, which is one of the major concerns of the research and the discussion that takes place there. "I can not think of anything better designed to confuse the public and foster greater mistrust of the science of nutrition and science in general," said Marion Nestle, Paulette Goddard Professor of Nutrition, Food Studies. and Public Health, Emeritus, at the University of New York. . Dietary advice is confusing, she said, and changing goals can lead people to disregard all advice and not worry about best practices.
Part of the confusion comes from the attention paid to individual food types (meat, eggs, etc.), which makes nutrition seem to be a more moving target than it tends to be, D 'said Adamo. Overall, most experts agree. "When we choose a single part of the diet as the only problem, which has been solved with red meat, among other things, we are missing the larger picture. This amounts to eating more whole foods and minimizing processed foods. "