Last month, the Annals of Internal Medicine published an article co-authored by Dr. Bradley C. Johnston — an associate professor at Dalhousie University — that criticizes the scientific backing of public health advice to eat less red meat in order to counter heart disease, diabetes, and other conditions.
Johnston’s study attacked the quality of research of other nutritional studies with a method named the Grading of Recommendations, Assessment, Development and Evaluation (GRADE), which is used to judge the quality of clinical drug trial research.
GRADE ranks studies based on precision and accuracy. Due to GRADE’s design, it automatically ranks the “large observational studies and randomized trials” common in nutritional science as low-quality research.
Johnston and his team, evaluating the nutritional studies that link meat consumption and health ailments using the tool, could conclude that all studies that find this connection are low quality. As a consequence, this delegitimizes nutritional science.
But the nutritional science community has been vocal in its opposition of the study, largely citing a misuse of GRADE. “You can’t do a double-blinded placebo-controlled trial of red meat and other foods on heart attacks or cancer,” Dr. Frank Hu of the nutrition department at the Harvard T.H. Chan School of Public Health said to The New York Times. “For dietary and lifestyle factors, it’s impossible to use the same standards for drug trials.”
Dr. David Jenkins, a U of T professor in the Department of Nutritional Sciences and Faculty of Medicine, has also been vocally opposed to this methodology. “What [nutritional scientists] rely on is perspective cohorts — [we]take a group of people and follow them over time and work out what they’ve eaten and what their lifestyle is,” Jenkins told The Varsity. “It works well, but people who smoke, [for example,] tend to have other bad habits.”
In other words, it’s hard to control for a single factor, and thus GRADE “automatically ranks these studies as low-quality, even if there is a consistent response.”
The misuse of GRADE has real-world repercussions on the face of public health. “I’m concerned about the damage that has already been done to public health recommendations,” Hu told The New York Times. “Certainly, the data are regarded as low-quality [according to GRADE] — let’s accept that,” said Jenkins.
“But it’s not about just one thing. It doesn’t just relate to diabetes or heart disease or an increased cancer incidence — it relates to all of them. Surely, then there must be some significance. It’s the scope… it’s not strong, it’s broad.”
In response, public health organizations are taking action. For example, the Physicians Committee for Responsible Medicine, which advocates for veganism, filed a petition to the Federal Trade Commission against the journal that published the article due to concerns that it delivers “dangerous advice.”
Furthermore, Johnson was a senior author on a study aiming to discredit international health guidelines that advised against high sugar consumption. The study was sponsored by food and pharmaceutical companies like Pepsico and McDonald’s.
Jenkins also ventures that health should not be the only motivating factor in considering to eat less meat. “We’ve got a global warming situation,” he warns. “We have as many — or more — four legged friends that we eat on the planet than there are of ourselves. We have to consider all the mechanization that’s used to produce feed for them, which use fossil fuels, and all the required energy and land.”
Dr. Gordon Guyatt, the chair of the peer review panel for the article, said to Coast Mountain News that it is “hysterical… It’s completely predictable and they’re doing themselves no favours from my point of view about these sort of hysterical statements.”
Jenkins is nevertheless eager to reach a point of agreement in the meat debate. “It’s not low quality about just one thing. It doesn’t just relate to diabetes or heart disease or an increased cancer incidence — it’s related to all of them.”