Dietary guidelines from groups as diverse as the Department of Agriculture to the World Health Organization urge all of us to eat less red meat — much less.
But the authors of four new studies, published on Wednesday in the Annals of Internal Medicine, report there is no compelling evidence that reducing consumption of red or processed meats will be beneficial to an individual.
A furious backlash is already unfolding. Here are five takeaways from the debate.
Nutrition studies often do not meet the most rigorous scientific standards.
The majority of nutrition studies are observational — in the case of red meat, they asked if meat-eaters were less healthy, and if those who ate more were also less healthy than those who ate less.
But it’s extremely difficult to know what someone is eating; many study participants struggle to remember and accurately report their diets. And meat-eaters may differ from those who don’t eat meat, or eat less, in a variety of ways that also influence health.
Researchers try to correct for those variations, but the statistical analyses are difficult and, many experts say, not particularly reliable in a system as complex as human nutrition.
Even in the best of circumstances, observational studies do not prove cause and effect; they only suggest correlations. But policymakers often rely on this data when devising guidelines.
The studies sometimes do turn up small health benefits from eating less meat.
Here are some of the outcomes cited by the authors of the new research: If people were to reduce meat consumption by three servings a week, there might be one to six fewer heart attacks per 1,000 people. But there would be no effect on deaths resulting from heart disease or any cause over all.
For cancer, the group reports that decreasing meat consumption by three servings a week might result in seven fewer cancer deaths per 1,000 people. But there would be no effect on the risk of getting breast, colorectal, esophageal, gastric, pancreatic or prostate cancer.
But what does that mean for you personally?
Frank Hu, professor and chair of the nutrition department at the Harvard T.H. Chan School of Public Health, wrote in an email:
“These risk reductions are not small from a public health point of view and could save hundreds and thousands of lives in the U.S., because of the high prevalence of people consuming diets high in red and processed meats. Few dietary or lifestyle changes or even a drug could have multiple health benefits on major causes of deaths.”
But Dr. Dennis Bier of Baylor said the studies of meat consumption are so flawed that it is naïve to assume these risk reductions are caused by eating less meat.
“The rules of scientific proof are the same for physics as for nutrition,” he said in a telephone interview. But unlike experiments in physics, where investigators can control variables and determine causality, in nutrition “you can’t conduct the experiment.”
Major medical organizations are sticking to their dietary recommendations.
The American Cancer Society and the American Heart Association, among others, immediately released statements reiterating their advice to eat less red meat for better health.
We’re all going to have to live with some uncertainty about what to eat.
“The guidelines are based on papers that presumably say there is evidence for what they say. And there isn’t. That’s the history of nutrition,” said Dr. Bier.
Dr. David Allison, dean of the Indiana University School of Public Health — Bloomington, said there is a difference “between evidence for drawing a scientific conclusion, and making or recommending an action.”
“The standards of evidence for the former are scientific matters and should not depend on extra scientific considerations” he added. “The standards of evidence for the latter are matters of personal judgment or in some cases legislation.”
His advice: “People should be aware of the uncertainty and make their decisions based on that awareness.”
