To eat meat, or not to eat meat: That is a question scientists and omnivores have grappled with for decades, and will contend with for years to come amid increasing consumption. But a new study, the most wide-ranging of its kind, claims that meat can in fact be part of a healthy diet — with two major caveats.

Drawing on survey data from 21 countries, with 80% of participants in low-income nations, researchers from around the world showed that eating about 250 grams per week of unprocessed meat such as beef, mutton, veal or pork does not increase risk of death or cardiovascular disease. In contrast, they saw a strong association with both when people consumed as little as 150 grams of processed meats such as bacon and other cured, additive-laden meats. 

The researchers describe their findings in a study published March 31 in the American Journal of Clinical Nutrition. 

"When we started, we really didn't know if we'd find increased risk or decreased risk, and we were pleased to see a neutral association" regarding unprocessed meat, said corresponding author Mahshid Dehghan, an investigator at the Population Health Research Institute in Canada. "That was the wow factor for us, because it was supporting the hypothesis we had that fresh food should not be unhealthy if consumed in moderate amounts."

Examining about 135,000 survey participants, the researchers saw 7,789 deaths and almost 7,000 cardiovascular disease events such as heart attack, stroke and heart failure. After they controlled for variables such as smoking, education and physical activity, the numbers revealed no clear association between moderate unprocessed meat consumption and these disease events. 

For example, the number of survey participants who ate 250 or more grams of unprocessed meat and those who ate 50 grams or fewer was roughly the same, at about 38,000. And each tended to have similar rates of heart failure, stroke and cancer deaths over nine-and-a-half years of data. 

Meanwhile, processed meat eaters, even those who ate moderate amounts of around 150 grams or more per week, saw higher rates of fatal cancer, major cardiovascular disease, heart attack and stroke, compared with those who ate less. 

For instance, just over 3,000 participants ate zero grams of processed meat per week, and suffered 39 heart attacks. In contrast, of the 3,111 who ate 150 grams or more, 73 experienced heart attacks. 

Unlike the rest of the survey, however, data regarding processed meat intake was limited to eight countries, as most people in the low-income countries involved eat virtually no processed meat products.

Processed meat already has a bad reputation for its high salt and nitrate content. In 2015, the World Health Organization listed processed meat products as a group 1 carcinogen, meaning that substantial epidemiological evidence shows that they can cause cancer, especially colon cancer.

The data behind the new study comes from the Population Health Research Institute's ongoing Prospective Urban and Rural Epidemiological, or PURE study. With it, Dehghan and her colleagues set out to present a clearer picture of the health effects of eating meat. While a number of studies and meta-analyses already point to the safety of moderate meat consumption, findings have been inconsistent, with some papers claiming that regularly eating meat increases mortality risk. 

According to Dehghan, these studies tend to focus on western countries like the U.S., where citizens ate 114 pounds of red meat per capita in 2020. Instead of drawing on narrower datasets representing a relatively small part of the world, Dehghan wanted to use the PURE study to provide new evidence from less-studied areas, like rural India and rural China, to draw more accurate conclusions about the health effects of eating meat. 

Still, because so many of the survey participants are from poorer countries where meat is not consumed as much as in the U.S., this paper could not, nor did it, attempt to study the outcomes of frequent meat consumption. 

"We cannot rule out the harm of very high meat consumption," Dehghan said. "We are saying with moderate unprocessed meat consumption, up to 250 grams per week, there is no harm. We don't say stop eating meat. We are saying 'Have meat, but one or two servings per week, that's fine.'"

Dehghan plans to keep using PURE study data to fuel her research in diet and health outcomes. Her next project will examine associations between ultra-processed foods such as chips, mass-produced baked goods and sausage products. 

According to Dehghan, the additives in processed foods, along with colorings and even packaging, could potentially trigger negative physiological reactions because the human body is not used to them and cannot metabolize them.

"We really like to encourage people to avoid processed meat, and by avoiding processed meat we may reduce numbers of cardiovascular disease and mortality, especially among frequent consumers," she said.

The study, "Associations of unprocessed and processed meat intake with mortality and cardiovascular disease in 21 countries [Prospective Urban Rural Epidemiology (PURE) Study]: a prospective cohort study," published March 31 in the American Journal of Clinical Nutrition, was authored by Romaina Iqbal, Aga Khan University; Mahshid Dehghan, Andrew Mente, Sumathy Rangarajan, Koon Teo and Salim Yusuf, McMaster University; Andreas Wielgosz, University of Ottawa; Alvaro Avezum, University of Santo Amaro; Pamela Seron, University of La Frontera; Khalid F. AlHabib, King Saud University; Patricio Lopez-Jaramillo, University of Santander; Sumathi Swaminathan, St. John's Research Institute; Noushin Mohammadifard, Isfahan University of Medical Sciences; Katarzyna Zato'nska, Wroclaw Medical University; Hu Bo, Yin Lu and Liu Xiaoyun, Peking Union Medical College; Ravi Prasad Varma, Sree Chitra Tirunal Institute for Medical Sciences and Technology; Omar Rahman, University of Liberal Arts Bangladesh; AfzalHussein Yusufali, Dubai Medical University; Noorhassim Ismail, University Kebangasan Malaysia; Annika Rosengren, University of Gothenburg;  Ne¸se Imeryuz, Marmara University; Karen Yeates, Queen's University and Pamoja Tunaweza Research Center; Jephat Chifamba, University of Zimbabwe; Antonio Dans, University of the Philippines Manila; Rajesh Kumar, Postgraduate Institute of Medical Education and Research, Chandigarh; Lungi Tsolekile, University of the Western Cape; Rasha Khatib, Birzeit University and Advocate Research Institute; and Rafael Diaz, Clinical Studies Latin America, Rosario, Santa Fe, Argentina.