Bacon causes cancer? Sort of. Not really. Ish.

BY SARAH ZHANG 10.27.15. 7:00 AM.

PERHAPS NO TWO words together are more likely to set the internet aflame than BACON and CANCER. So when the World Health Organization classified processed meat as a group 1 carcinogen, the same category as tobacco—

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.

What the IARC doesn’t do—and where things get a lot fuzzier—is risk assessment, or figuring out the danger to humans in the real world. Risk assessment involves looking at different scenarios, finding out real-world exposure levels, and weighing possible benefits. (Useful drugs like Tamoxifen—used to treat breast cancer—are also carcinogens, for example.) Those factors can vary from person to person, country to country. “The issue of whether the monograph program should be amended to also include risk assessment has been raised several times, and each time,” says Boffetta, “the conclusion was it should not. It should let national regulatory agencies do the research.” And after 50 years of doing things one way, it’s not like the IARC can just change its mind.

In a way, the IARC’s commitment to, as Boffetta calls it, “an independent list that was not subject to additional pressures,” makes a kind of sense. But science doesn’t happen in a vacuum—just look at the wave of traffic that crashed the IARC’s website after the meat announcement. The agency can maintain that it’s a dispassionate resource for policymakers, but the public is knocking at its door.

In recent years, says Boffetta, the agency has gotten a lot of attention each time it classified something, and those actions often get “overinterpreted.” “X causes cancer” does not mean that X will definitely give you cancer; it just means that X increases your risk of cancer by some amount, and it can vary wildly from a tiny tiny percentage to 25 fold. Does bacon cause cancer? Sure. A little. Will bacon cause cancer in you? Probably not.


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