However, recently, an international group of researchers conducted an analysis and concluded that the advice, widely given by health officials and advisors, isn't backed by reliable scientific evidence.
If there are health benefits from eating less red meat, they're small, the researchers said. They contend the advantages are so small that they can be seen only when looking at large populations, and aren't sufficient to tell consumers to change their meat-eating habits.
Bradley Johnston, an epidemiologist at Dalhousie University in Canada, is the leader of the group that published the new research in the Annals of Internal Medicine.
The average American eats about 4½ servings of red meat a week, according to the Centers for Disease Control and Prevention. About 10 percent of the population eats at least two servings a day.
The new analysis
Over three years, a group of 14 researchers in seven countries, along with three community representatives, were directed by Johnston. The investigators said they had no conflicts of interest and did the studies without outside funding. However, after the study was released, a New York Times article reported Johnston does have ties to industry.
The group reviewed 61 articles reporting on 55 populations, with more than 4 million participants. The researchers also looked at the few randomized trials linking red meat to cancer and heart disease, as well as 73 articles that examined links between red meat and cancer incidence and mortality.
Marion Nestle, nutritionist, and other health officials, say the new research is faulty.
"This is a good example of what I call nutritional nihilism, an approach that insists that because observational studies are based on self-reported information and necessarily flawed, their conclusions are unscientific and should be discounted," Nestle said in a blog post. "Therefore, because we can’t do more rigorous studies, we should not advise the public about diets best for health or the environment."
Nestle's concerns are:
- The effects are small but that's true of nutrition studies in general. The small effects show benefits from eating less meat. The authors could easily have interpreted their work as suggesting that eating less meat might be useful. This is an example of interpretation bias.
- The authors took a strictly science-based approach to a problem strongly affected by social, economic, and political factors and values.
- The studies look at previous studies that compared people who eat meat to those who eat less. The authors excluded studies of vegetarians compared to meat-eaters.
- They look at meat outside its context of calories.
- The authors didn't look at the totality of the evidence; they excluded laboratory and animal studies that can be more closely controlled.
- They excluded studies of environmental impact, which has a significant bearing on human dietary practices (meat production adds more greenhouse gases than vegetable production).
- The conclusions fall into the category of “everything you thought you knew about nutrition is wrong.” This rarely happens. Science usually works incrementally, not in one enormous reversal like this.
Do the authors really believe that all those other committees and commissions urging less meat were wrong and continue to be wrong? Nestle asks, adding their strictly science-based approach seems unrealistic.
Nestle said the papers come across to her as a concerted attack on dietary guidelines (national and international), on nutrition science in general, and on nutritional epidemiology in particular.
"The meat industry and its supporters will love them," she said.
Nestle said attacks on the quality of nutrition research have been coming from many sources lately: the food industry, but also statisticians (John Ioannidis at Stanford is making a career of this), and some scientists (usually with ties to food companies). The criticisms themselves are not new.
"What is new is the vehemence and level of effort to discredit observational studies, particularly those based on self-reports of dietary intake," Nestle said. "Yes, nutritional epidemiology has flaws, but the methods have been useful in many instances, as argued convincingly by two of its leading practitioners."
In looking at nutrition research, she thinks it's essential to evaluate the totality of information available: laboratory, animal, human epidemiology, and clinical studies — and to do this in the context of what people actually eat and the number of calories they consume, as well as adding in a hefty dose of common sense.
"Common sense is what’s missing in these studies," Nestle said. She asks whether the authors really believe that:
- Meat eaters are healthier than vegetarians?
- Eating more meat is better for health?
- Meat eaters are less obese and have less heart disease and cancer than those who eat less?
"If not, the conclusions make no sense," she said.
Most of the authors report no financial ties to the food industry, Nestle said. "I would love to know the back story about why they chose to do these studies and to interpret them in this way."
Reactions to the new study
- The Harvard School of Public Health Nutrition Department issued a statement
- The True Health Initiative (THI) issued a press release outlining its concerns (the link is here)
- THI council members sent a letter to the journal editor stating objections (the link)
- THI collected quotes from members of its council and others (including mine)
- David Katz weighs in
- New York Times: 5 things you should know
- New York Times coverage: “Eat less meat, scientists said. Now some believe that was bad advice.”
- From Dean Ornish
- Consumer Reports
- From the World Cancer Research Fund
- Vox’s crystal clear explanation
- NPR’s The Salt’s excellent analysis
- Aaron Carroll’s follow-up to his editorial
See the Consumer Reports article "Nutrition: Healthy Eating — Does It Matter How Much Meat You Eat?" for more information on the study, including the impacts of eating meat on the environment.