Is red meat healthy? A closer look at a controversial conclusion
Earlier this month, research published in Annals of Internal Medicine turned heads in the nutrition field and popular press. The main takeaway: despite common dietary guidelines, scientific evidence does not justify recommendations to eat less red meat.
The international team of researchers aimed to shed light on conflicting research. They noted that while some studies have shown associations between red meat intake or processed meat health conditions such as cardiovascular mortality, stroke, coronary heart disease, and type 2 diabetes, results have not been consistent. They hypothesized that the conflicting studies could be due to methodological limitations such as “failure to address risk of bias of primary studies.”
“These limitations may have affected the credibility of recommendations issued by governments and authoritative organizations regarding red and processed meats,” write Zeraatkar et al.
The researchers took a closer look at past studies. They published their results as a series of five systemic reviews:
- Red and Processed Meat Consumption and Risk for All-Cause Mortality and Cardiometabolic Outcomes: A Systematic Review and Meta-analysis of Cohort Studies
- Effect of Lower Versus Higher Red Meat Intake on Cardiometabolic and Cancer Outcomes: A Systematic Review of Randomized Trials
- Reduction of Red and Processed Meat Intake and Cancer Mortality and Incidence: A Systematic Review and Meta-analysis of Cohort Studies
- Patterns of Red and Processed Meat Consumption and Risk for Cardiometabolic and Cancer Outcomes: A Systematic Review and Meta-analysis of Cohort Studies
- Health-Related Values and Preferences Regarding Meat Consumption: A Mixed-Methods Systematic Review
The researchers reported that their review of 12 trials with 54,000 people did not show a statistically significance or important association between meat consumption and risk of heart disease, diabetes, or cancer. Overall, from 61 scientific articles reporting on 55 cohorts with more than 4 million participants, the researchers found a small reduction in risk for people who had three fewer serving of red or processed meat each week, but the association was “uncertain.”
“Because they review all of the evidence that came before, they cannot be accused of cherry-picking,” wrote Aaron E. Carroll and Tiffany S. Doherty in an editorial for Annals of Internal Medicine.
As a Los Angeles Times editorial put it: “The latest flip-flop on red meat uses best science in place of best guesses.”
Of course, a lack of evidence of harm is not the same as concluding that these foods are certainly safe. The researchers address this difference in their recommendations that "adults continue current unprocessed red meat consumption” and “adults continue current processed meat consumption.” These recommendations come with the note: “weak recommendation, low-certainty evidence.” Still, the recommendations are based on rigorous analysis of the body of evidence, rather than individual studies subject to bias.
Meanwhile, nutrition researchers say the new analysis itself is flawed. According to a Harvard commentary, “This is a prime example where one must look beyond the headlines and abstract conclusions.”
The Harvard team argues that the strategy of combining datasets in a “meta-analysis” actually clouds the data. They say a majority of studies cited did show negative outcomes tied to meat consumption. “Across the board, these studies found a statistically significant association of lower consumption of red meat and processed meats and lower total, CVD, and cancer mortality and incidence of type 2 diabetes,” they write.
However, the Annals of Internal Medicine reviews aren’t the only recent studies to call commonly accepted nutrition guidelines into question. A recent publication in BMJ Evidence-Based Medicine showed that saturated fats, which can be found in foods such as meat and cheese, do not affect mortality.
Where should researchers and policymakers go from here? Gordon Guyatt, a member of the red meat study research team told Feedstuffs, “There is a worldwide interest in nutrition and the issue of red meat in particular. People need to be able to make decisions about their diet based on the best information available.”