Hold on. Let me stop right here. Eating bacon is not as bad as smoking when it comes to cancer. Just no.
The way WHO classifies cancer-causing substances, on the other hand? Maybe a little dangerous to your mental health. Because it is really confusing.
Here’s the deal: The WHO’s International Agency for Research on Cancer weighs the strength of the scientific evidence that some food, drink, pesticide, smokable plant, whatever is a carcinogen. What it does not do is consider how much that substance actually increases your risk for actually getting cancer—even if it differs by magnitudes of 100.
The scientific evidence linking both processed meat and tobacco to certain types of cancer is strong. In that sense, both are carcinogens. But smoking increases your relative risk of lung cancer by 2,500 percent; eating two slices of bacon a day increases your relative risk for colorectal cancer by 18 percent. Given the frequency of colorectal cancer, that means your risk of getting colorectal cancer over your life goes from about 5 percent to 6 percent and, well, YBMMV. (Your bacon mileage may vary.) “If this is the level of risk you’re running your life on, then you don’t really have much to worry about,” says Alfred Neugut, an oncologist and cancer epidemiologist at Columbia.
The link, though tiny, may start with an iron-based chemical called heme, found in red meat. Heme breaks down into carcinogenic N-nitroso compounds in the digestive tract. Partially on this basis, the IARC also classified unprocessed red a “probable carcinogen.” But processed meat takes it a step further: The nitrates and nitrates used to cure meat—which is to say, preserve it—also turn into N-nitroso compounds. Grilling, frying, or otherwise cooking the meat at high-temperatures may create yet other cancer-causing compounds.
So it makes sense that cutting down on bacon, hot dogs, salami, and ham reduce cancer risk a little. But it’s hardly the big deal that quitting tobacco would be. Connecting the two, as The Guardian does in its headline, “Processed meats rank alongside smoking as cancer causes—WHO,” misrepresents the IARC’s conclusions.
The IARC is an organization of scientists, not policy makers. It publishes monographs to identify hazards and sift them into five piles: group 1 (carcinogenic), group 2A (probably carcinogenic), group 2B (possibly carcinogenic), group 3 (not classifiable), and group 4 (probably not carcinogenic.) Group 1 includes processed meat, and also asbestos. Also alcohol (boo!) and sunlight (yup!). Identifying hazards involves looking at existing data—lots and lots of it—to do essentially a meta-analysis of studies already out there. And it’s relatively objective. “Hazard identification is the process that is the closest to the generation of scientific data,” say Paolo Boffetta, a cancer epidemiologist at Mount Sinai who has served on similar WHO panels. In other words, IARC studies the studies and generates numbers.