It’s official: Processed meat — such as hot dogs, bacon, corned beef and salami — causes cancer.
Years of evidence and numerous studies have linked processed meat to colorectal, or bowel, cancer. Now, after reviewing more than 800 epidemiological studies, the World Health Organization has designated such meats as carcinogenic. WHO made the announcement online October 26 in The Lancet Oncology.
WHO’s International Agency for Research on Cancer classifies processed meat — meat altered through salting, curing, fermenting or smoking — as a Group 1 carcinogen. This group of cancer-causing agents also includes smoking and asbestos. The ranking means there’s convincing evidence linking the modified meats to colorectal cancer, evidence as strong as that linking smoking to cancer.
This does not mean that eating processed meat is as risky as smoking. An analysis by the research charity group Cancer Research UK in London offers some perspective: Research suggests that 61 people per 1,000 in the United Kingdom will develop bowel cancer during their lives. Among those 1,000 who eat the most processed meat, you’d expect 66 to develop bowel cancer, while among those who eat the least processed meat, about 56 would develop bowel cancer.
The IARC also classified red meat, (beef, veal, mutton, lamb, pork, horse and goat) as “probably carcinogenic.” This Group 2A classification means eating red meat was correlated with an increased risk for some cancers including bowel, pancreatic and prostate, but other explanations for the increase couldn’t be ruled out.
In the IARC evaluation, prospective cohort studies, which follow large groups of healthy people and track information on exposures as they go along, were given the most weight. Additional evidence came from case-controlled studies, which look at people who are already sick and ask them about things like their food habits before they got cancer. While evidence linking processed meats and bowel cancer was the strongest, some studies also suggested a link between processed meat and stomach cancer and red meat and pancreatic and prostate cancer.
The IARC doesn’t make diet recommendations, but other organizations have been suggesting for years that people limit their intake of red and processed meat.
“This is an important step in helping individuals make healthier dietary choices to reduce their risk of colorectal cancer in particular,” Susan Gapstur, vice president of epidemiology at the American Cancer Society, said in a statement.
The London-based World Cancer Research Fund recommends eating no more than 500 grams of red meat per week, and eating as little as possible of processed meats. One hot dog is about 45 grams; 100 grams is roughly a portion the size of a deck of cards — slightly less than a quarter-pound hamburger, for instance.
Several cancer-causing mechanisms are probably at play, the IARC notes. Curing and smoking meat can generate nitroso compounds, which damage DNA. High amounts of iron — found naturally in red meats — also increase production of these compounds.
The way meat is prepared may raise cancer risks, too. The high temperatures of pan frying, grilling and broiling can produce aromatic amines (also found in tobacco smoke), which do cellular damage.
It may seem counterintuitive that something like meat, part of the human diet for ages, could be bad for you, says Mariana Stern, a cancer epidemiologist from the University of Southern California in Los Angeles. She was one of the 22 scientists on the IARC panel. In fact, meat does provide important proteins and other micronutrients such as B vitamins, iron and zinc, the IARC notes. But quantity and life expectancy are different today than in the past, Stern says.
“Age is the biggest carcinogen that we have,” she says. “We’ve been eating meat for a long time, but currently, we may be eating it in much higher amounts and our life expectancy is higher so we have more time to develop cancers.”