New reviews contradict previous guidelines around red meat consumption

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New guidelines based on five reviews of existing evidence have recently made the headlines for suggesting that people could go on eating red meat — processed and unprocessed — without fearing ill health consequences. But how should we interpret these findings?

Numerous studies have suggested that consuming processed or unprocessed red meat is associated with a higher risk of cancer, cardiovascular problems, and premature death, among other negative health outcomes.

Based on this and similar evidence, national and international policymakers have issued guidelines recommending that individuals reduce their intake of red meat as much as possible.

Such guidelines include the 2015–2020 Dietary Guidelines for Americans and the United Kingdom’s National Health Service recommendations regarding red meat consumption.

Yet over the past few days, a controversial new set of guidelines has made headlines worldwide, as the findings suggest that red meat may not have as detrimental an impact on health as researchers previously thought.

The guidelines — available in full via the Annals of Internal Medicine — have elicited backlash from researchers and physicians around the world, who have expressed concern.

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But where do these new guidelines come from, and what do they actually say?

The rationale behind the reevaluation

The panel of authors that issued the new set of recommendations includes 19 diet and nutrition specialists, who form part of an independent research group called the Nutritional Recommendations (NutriRECS) Consortium.

In their published paper, the NutriRECS researchers explain that they had seen a need to reevaluate existing evidence about the relationship between red meat consumption and negative health outcomes for several reasons.

First, the authors state, existing recommendations are “primarily based on observational studies” that are often unable to establish cause and effect relationships and do not “report the absolute magnitude of any possible effects.”

The team also alleges that “The organizations that produce guidelines did not conduct or access rigorous systematic reviews of the evidence, were limited in addressing conflicts of interest, and did not explicitly address population values and preferences.”

For these reasons, the NutriRECS researchers decided to reevaluate the existing evidence, conducting five systematic reviews. The reviews looked at dozens of randomized trials and observational studies, including thousands of participants among them.

To assess the evidence derived from those studies, the researchers developed their own method of evaluation based on the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) method.

The GRADE method essentially categorizes evidence according to rates of certainty, thus:

very low certainty, if the true effect of a factor is probably significantly different from the estimated effect

low certainty, if the true effect of a factor is possibly significantly different from the estimated effect

moderate certainty, if the true effect of a factor is likely close to the estimated effect

high certainty, if the true effect of a factor is almost certainly close to the estimated effect

What did the reviews find?

In 4 of the 5 reviews, the researchers looked at whether a realistic reduction in red meat intake had any effect on the risk of certain negative health outcomes, including all-cause mortality, cardiovascular mortality, stroke, heart attack, diabetes, cancer incidence, and mortality related to cancer.

They defined a «realistic» reduction in red meat intake as a reduction by 3 servings per week, for example, by going from 7 to 4 servings of red meat per week.

This definition, the authors explain in their paper, is based on the fact that «The average intake of [red meat is] 2–4 servings per week in North America and Western Europe.»

After evaluating the evidence presented by relevant studies, the researchers concluded that, while there may be an association between the consumption of red meat and the risk of poor health outcomes, it is unclear that eating this type of meat would really have a significant negative effect on health.

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