according to recent guidelines from an international panel that were recently published in the Annals of Internal Medicine.
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This recommendation was based on the panel having found “low- to very-low-certainty evidence that diets lower in unprocessed red meat may have little or no effect on the risk for major cardiometabolic outcomes and cancer mortality and incidence.” Additionally, meta-analysis results from 23 cohort studies provided low- to very-low-certainty evidence that decreasing unprocessed red meat intake may result in a very small reduction in the risk for major cardiovascular outcomes and type 2 diabetes, with no statistically differences in all-cause mortality and cardiovascular mortality, the guidelines say.
“Our weak recommendation that people continue their current meat consumption highlights both the uncertainty associated with possible harmful effects and the very small magnitude of effect, even if the best estimates represent true causation, which we believe to be implausible,” Bradley C. Johnston, PhD, of the department of community health and epidemiology at Dalhousie University, Halifax, N.S., and colleagues wrote in their paper summarizing the panel’s guidelines.
The evidence Dr. Johnston and colleagues examined were from four systematic reviews analyzing the health effects of red meat and processed meat consumption in randomized trials and meta-analyses of cohort studies as well as one systematic review that identified how people viewed their consumption of meat and values surrounding meat consumption.
In one review of 12 randomized trials examining diets of high and low red meat consumption, a diet consisting of low red meat had little effect on cardiovascular mortality (hazard ratio, 0.98; 95% confidence interval, 0.91-1.06), cardiovascular disease (HR, 0.99; 95% CI, 0.94-1.05), all-cause mortality (0.99; 95% CI, 0.95-1.03) and total cancer mortality (HR, 0.95; 95% CI, 0.89-1.01), including on colorectal cancer or breast cancer (Zeraatkar D et al. Ann Intern Med. 2019 Oct 1. doi: 10.7326/M19-0622). A different review of observational cohort studies with more than 1,000 participants found “very-small or possibly small decreases” in all-cause mortality, incidence, and all-cause mortality of cancer, cardiovascular mortality, nonfatal coronary heart disease and MI, and type 2 diabetes for patients who had a diet low in red meat or processed meat (Vernooij R et al. Ann Intern Med. 2019 Oct 1. doi: 10.7326/M19-1583); a second review by Zeraatkar and colleagues of 55 observational cohort studies with more than 4 million participants found three servings of unprocessed red meat and processed meat per week was associated with a “very small reduction” in risk for MI, stroke, type 2 diabetes, cardiovascular mortality, and all-cause mortality (Zeraatkar D et al. Ann Intern Med. 2019 Oct 1. doi: 10.7326/M19-1326). Another systematic review of 56 observational cohort studies found three servings of unprocessed red meat per week was associated with a slight reduction in overall cancer mortality (Han MA et al. Ann Intern Med. 2019 Oct 1. doi: 10.7326/M19-0699).
The authors also performed a systematic review of participant preferences and values regarding meat consumption. The evidence from 54 qualitative studies showed omnivores preferred eating meat, considered it part of a healthy diet, “lack[ed] the skills needed” to prepare meals without meat, and were mostly unwilling to change their meat consumption (Valli C et al. Ann Intern Med. 2019. doi: 10.7326/M19-1326).
“There was a very small and often trivial absolute risk reduction based on a realistic decrease of three servings of red or processed meat per week,” Dr. Johnston and colleagues wrote in their guidelines. If the very-small exposure effect is true, given peoples’ attachment to their meat-based diet, the associated risk reduction is not likely to provide sufficient motivation to reduce consumption of red meat or processed meat in fully informed individuals, and the weak, rather than strong, recommendation is based on the large variability in peoples’ values and preferences related to meat.”
The authors noted they did not examine factors such as cost, acceptability, feasibility, equity, environmental impact, and views on animal welfare when creating the guidelines. In addition, the low level of evidence from the randomized trials and observational studies means that the potential benefits of reducing red meat or processed meat intake may not outweigh the cultural and personal preferences or quality of life issues that could arise from changing one’s diet.
“This assessment may be excessively pessimistic; indeed, we hope that is the case,” they said. “What is certain is that generating higher-quality evidence regarding the magnitude of any causal effect of meat consumption on health outcomes will test the ingenuity and imagination of health science investigators.”
Dr. El Dib reported receiving funding from the São Paulo Research Foundation, the National Council for Scientific and Technological Development, and the faculty of medicine at Dalhousie University. Dr. de Souza reports relationships with the Canadian Institutes of Health Research/Health Canada, the Canadian Foundation for Dietetic Research and the World Health Organization in the forms of personal fees, grants, and speakers bureau and board of directorship appointments. Dr. Patel reports receiving grants and person fees from the National Institutes of Health, Sanofi, the National Science Foundation, XY.health, doc.ai, Janssen, and the CDC.
SOURCE: Johnston B et al. Ann Intern Med. 2019 Oct 1. doi: 10.7326/M19-1621.