Controversial review finds that cutting back on red and processed meat has little health impact

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A major international set of systematic reviews has concluded that cutting back on red and processed meat has little impact on health, contrary to current nutritional guidelines. The lead author of the EAT-Lancet Commission, which in January advocated a plant-based diet for both environmental sustainability and health, excoriated the findings as flawed and a “most egregious abuse of evidence.

Research that claims red and processed meat is probably not harmful to our health has caused controversy among experts who maintain people should cut down. Most people can continue to eat red and processed meat as they do now. A major study led by researchers at McMaster and Dalhousie universities has found cutting back has little impact on health.

Research that claims red and processed meat is probably not harmful to our health has caused controversy among experts who maintain people should cut down. Most people can continue to eat red and processed meat as they do now. A major study led by researchers at McMaster and Dalhousie universities has found cutting back has little impact on health.

A panel of international scientists systematically reviewed the evidence and have recommended that most adults should continue to eat their current levels of red and processed meat. The researchers performed four systematic reviews focused on randomised controlled trials and observational studies looking at the impact of red meat and processed meat consumption on cardiometabolic and cancer outcomes.
In three systematic reviews of cohort studies following millions of people, a very small reduction in risk among those who had three fewer servings of red or processed meat a week, but the association was uncertain.

The authors also did a fifth systematic review looking at people’s attitudes and health-related values around eating red and processed meats. They found people eat meat because they see it as healthy, they like the taste and they are reluctant to change their diet.

McMaster professor Gordon Guyatt, chair of the guideline committee, said the research group with a panel of 14 members from seven countries used a rigorous systematic review methodology, and GRADE methods which rate the certainty of evidence for each outcome, to move from evidence to dietary recommendations to develop their guidelines.

Bradley Johnston, corresponding author on the reviews and guideline, said the research team realizes its work is contrary to many current nutritional guidelines. “This is not just another study on red and processed meat, but a series of high-quality systematic reviews resulting in recommendations we think are far more transparent, robust and reliable,” said Johnston, who is a part-time associate professor at McMaster and an associate professor of community health and epidemiology at Dalhousie.

He added: “We focused exclusively on health outcomes, and did not consider animal welfare or environmental concerns when making our recommendations.

“We are however sympathetic to animal welfare and environmental concerns with a number of the guideline panel members having eliminated or reduced their personal red and processed meat intake for these reasons.”

The accompanying editorial by authors at the Indiana University School of Medicine said: “This is sure to be controversial, but is based on the most comprehensive review of the evidence to date. Because that review is inclusive, those who seek to dispute it will be hard pressed to find appropriate evidence with which to build an argument.”

Other researchers involved in the work included those from the Netherlands, Poland and Spain, including the IberoAmerican Cochrane and Polish Cochrane centres and the guideline committee included lay people as well as the scientists. Dena Zeraatkar and Mi Ah Han, a visiting professor from South Korea, also had leadership roles on the McMaster team working on the reviews.

There were no primary external funding sources.

Abstract
Description: Dietary guideline recommendations require consideration of the certainty in the evidence, the magnitude of potential benefits and harms, and explicit consideration of people’s values and preferences. A set of recommendations on red meat and processed meat consumption was developed on the basis of 5 de novo systematic reviews that considered all of these issues.
Methods: The recommendations were developed by using the Nutritional Recommendations (NutriRECS) guideline development process, which includes rigorous systematic review methodology, and GRADE methods to rate the certainty of evidence for each outcome and to move from evidence to recommendations. A panel of 14 members, including 3 community members, from 7 countries voted on the final recommendations. Strict criteria limited the conflicts of interest among panel members. Considerations of environmental impact or animal welfare did not bear on the recommendations. Four systematic reviews addressed the health effects associated with red meat and processed meat consumption, and 1 systematic review addressed people’s health-related values and preferences regarding meat consumption.
Recommendations: The panel suggests that adults continue current unprocessed red meat consumption (weak recommendation, low-certainty evidence). Similarly, the panel suggests adults continue current processed meat consumption (weak recommendation, low-certainty evidence).

Authors
Bradley C Johnston; Dena Zeraatkar; Mi Ah Han; Robin WM Vernooij; Claudia Valli; Regina El Dib; Catherine Marshall; Patrick J Stover; Susan Fairweather-Taitt; Grzegorz Wójcik; Faiz Bhatia; Russell de Souza; Carlos Brotons; Joerg J Meerpohl; Chirag J Patel; Benjamin Djulbegovic; Pablo Alonso-Coello; Malgorzata M Bala; Gordon H Guyatt

The lead author of the EAT-Lancet Commission, which in January advocated a plant-based diet for both environmental sustainability and health, excoriated the new work, reports The Guardian. “This report has layers of flaws and is the most egregious abuse of evidence that I have ever seen,” said Walter Willett, professor of epidemiology and nutrition at the Harvard TH Chan School of Public Health, himself a vegan.

He said many of the participants of the study were young and unlikely to succumb to illness in the short time period involved in the trials. “The magnitude of risk reduction by replacing red meat with healthy protein sources is similar to that of many drugs we use for treating high blood cholesterol and blood pressure, and we spend massive amounts of money on this,” he added.

Gunter Kuhnle, professor of nutrition and food science at the University of Reading, said the research was thorough but that the weak evidence of possible harm should be taken into account.

The report says the World Cancer Research Fund, which warns of links between red and processed meat and bowel cancer, did not accept the new interpretation of the evidence. Dr Giota Mitrou, director of research, said it “could be putting people at risk by suggesting they can eat as much red and processed meat as they like without increasing their risk of cancer.

Professor Louis Levy, head of nutrition science at Public Health England, said: “Globally, the evidence indicates that people who eat red and processed meat should limit their intake.

This study has gone down like a lead balloon, with many in the field disagreeing with how the findings have been interpreted. BBC News reports that this is despite statisticians broadly supporting the way the study has been conducted.

Public Health England officials said they had no intention of reviewing their advice on limiting meat intake. Dr Marco Springmann, from the University of Oxford, said the “dangerously misguided” recommendations “downplay the scientific evidence”, which, in any case, comes from a “small number of meat-eating individuals from high-income countries”. Professor Nita Forouhi, from the University of Cambridge, said: “They stated that the magnitude of the link is small, is it?”

But Kevin McConway, emeritus professor of applied statistics at the Open University, called it an “extremely comprehensive piece of work”. And Professor David Spiegelhalter, from the University of Cambridge, said: “This rigorous, even ruthless, review does not find good evidence of important health benefits from reducing meat consumption In fact, it does not find any good evidence at all.”

McMaster University material Annals of Internal Medicine abstract The Guardian report BBC News report

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