The World Health Organization announced on Monday that, after reviewing the science, it has found eating a lot of processed meat—such as bacon, sausage, hot dogs, and ham—can cause bowel cancer. Eating too much beef, pork, lamb, and other meat from mammals can probably cause bowel cancer cancer too, according to the report. "This decision doesn't mean you need to stop eating any red and processed meat, but if you eat lots of it, you may want to think about cutting down," Tim Key, a scientist for Cancer Research United Kingdom and the University of Oxford, told the BBC. Eating even less than two slices of bacon per day raises a person's risk of colorectal cancer by 18 percent, the BBC reports. (For the record, when Key says "red meat," he means meat from mammals, including pork.)
It may seem strange to think of red and processed meat as causing cancer. Americans eat a lot of red meat; it's hard to imagine such a common habit could cause serious illness. Indeed, eating red and processed meat doesn't cause cancer at nearly the same rates as, say, smoking cigarettes. Plus, eating moderate amounts of red meat can be healthy, because it does provide nutrients like protein and iron. Still, the risk is very real here. In fact, the science linking excess processed meat consumption and colorectal cancer is roughly as well-established as the science linking cigarettes and lung cancer, according to the new WHO classification.
Once upon a time, people found the idea that smoking could cause lung cancer hard to believe, but attitudes changed over time—slowly. Perhaps the public's consciousness will similarly shift with regard to heavy meat-eating. Below, a timeline of Western folks' slow acceptance of smoking and meat-eating as risk factors for some of society's most feared diseases:
1950: Scientists published some of the first substantive, case-control studies showing smoking causes lung cancer. At that time, "Americans may have been aware of the controversy over smoking," Gallup reports. "But widespread acceptance of the serious health risks was many years in coming. A substantial amount of doubt about the risks persisted even in 1969, after two major Surgeon General reports and after the first cautionary labels appeared on cigarette packs."
1954: A few years after those landmark case-control studies, researchers asked a sample of adults in Manchester what behaviors they thought could lead to cancer. Only two percent said "smoking."
1958: By this time, awareness of smoking's risk had increased. When public-health researchers asked adults in Edinburgh what they thought might lead to cancer, 22 percent cited smoking. Only four percent said food. Twenty-five percent thought "knocks, bumps, and bruises" caused cancer. Nearly everyone had heard that researchers thought smoking caused lung cancer, as another survey of Edinburgh residents found. But not everyone believed the research—especially not smokers, who comprised a little more than half of adults in the U.K. in 1958. Among smokers, "it was found that they tended to believe smoking only became 'dangerous' when one smoked rather more than they themselves did," researchers wrote.
1972: About 70 percent of Americans reported they believed smoking causes lung cancer.
1980s: Different science groups published some of the first studies suggesting those who eat the most processed meat are more likely to get colon cancer. (Check out the references in this paper.)
1999: Ninety-two percent of American adults said they think smoking causes lung cancer.
2002: Only a select number of non-scientists seem aware of the link between processed meats and colon cancer. In this year, a pair of Australian public-health researchers published the results of a survey that found 42 percent of vegetarians thought eating too much meat caused cancer. Only one percent of non-vegetarians thought the same.
2015: Things are slowly looking up for people's awareness of their diet's effect on cancer risk. In a survey conducted by the American Institute for Cancer Research, 38 percent of Americans correctly identified "cured meats" as a cancer risk factor. Thirty-five percent correctly identified "diets high in red meat." The bad news? Thirty-eight percent of Americans also identified "cell phones" as a cancer risk, despite the fact that the science behind these cell-phone-causes-cancer claims is mixed and preliminary.
There's been a lot of backlash online to reporting on the WHO's announcement about the science behind bowel cancer and processed and red meat. It's true that it's important not to overstate the risk of eating those meats. It's likely that a ham sandwich a few times a week can be part of a healthy diet. But it's also critical that we make sure we don't look away from this risk, even when it's tempting to do so. Remember, in 1958, almost everybody was aware of the research linking cigarettes and lung cancer, but only a little more than one in five believed it was actually true—and those who didn't believe lost out on a crucial opportunity to do something to reduce their cancer risk.