New 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.
The World Health Organization has classified red and processed meats as
cancer-causing. Aside from public health, calls are multiplying for people
to cut back on meat consumption because of the climate emergency and the
greenhouse gas emissions that come from animal farming.
However the 14-member international team led by Bradley Johnston an associate
professor of community health at Dalhousie University in Halifax, Canada,
concluded that those who like meat should not stop on health grounds. “Based
on the research, we cannot say with any certainty that eating red or processed
meat causes cancer, diabetes or heart disease,” he said.
Many scientists agreed with the team that the evidence from studies around
the world was generally poor. Some said that left them open to both
interpretations – either that meat could cause health harm or that it
did not. Others said Johnston and colleagues were wrong to exclude
environmental concerns about damage to the planet from clearing
forests and animal farming from their work.
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. “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, who advocates a
plant-based diet.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.
But the series of papers published in the Annals of Internal Medicine journal
used methodology most scientists said was thorough, pulling together data from
studies around the world and grading their results. The best studies were those
in which similar participants were randomly allocated to one diet or another.
“Among 12 randomised control trials enrolling about 54,000 individuals, we
did not find a statistically significant or an important association in the
risk of heart disease, cancer, or diabetes for those that consumed less red
and processed meat,” Johnston said.
In other, weaker studies involving millions of people, which simply observe
the effects of people’s usual diet, “we did find a small reduction in risk
amongst those who consumed three fewer servings of red or processed meat per
week. However, the certainty of evidence was low to very low,” he said. Dietary studies
are notoriously difficult to do because people may not
always eat what they say they do or may not remember.
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. “The message people need to hear is that we should be eating no more than
three portions of red meat a week and avoiding processed meat altogether.
We stand by our rigorous research of the last 30 years and urge the public
to follow the current recommendations on red and processed meat.”
Prof 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. “While it can form part of healthy diet, eating too much can increase your risk of
developing bowel cancer. Following a healthy, balanced diet based on the Eatwell
Guide is best for long-term health.”