What's So Bad About Bacon?

Bacon Causes Cancer. Why?
The World Health Organization declared processed meats like bacon and hot dogs a cause of cancer, on Monday. Why are they designated as more concretely a carcinogen than unprocessed red meat? Rick Wilking/Reuters

On Monday, the World Health Organization added processed meat to its list of substances it considers cancer-causing. Bacon, sausages and similar food products are unequivocally "carcinogenic to humans," wrote the International Agency for Research on Cancer (IARC), the cancer research arm of the WHO. Words like may be or might be make no appearance in the organization's statement.

Red meat, meanwhile, was also given a new designation: The WHO has classified it as "probably carcinogenic" to humans, a classification given to a large group of carcinogens that includes glyphosate, a widespread and controversial herbicide.

So what makes processed meat such an unambiguous health threat, compared with unprocessed red meat?

Well, as one might imagine, it's all in the process.

Processed meat is defined by the WHO as "meat that has been transformed" by way of "salting, curing, fermentation, smoking," or any other means to enhance the flavor or preserve it for a longer shelf life. That means bacon, hot dogs, sausage, beef jerky, canned meat and mostly anything else that isn't just a simple hunk of animal flesh falls under that category.

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These transformative processes typically involve adding chemical compounds to the meat, or preparing it in a way that inadvertently adds chemicals. And as nutritionist Atli Arnarson points out, these additives can transform into compounds that have been linked to cancer when the meat product is being made, or while it is being cooked.

For example, nitrites are often added to packaged meat products like hot dogs as a preservative. These compounds slow the growth of bacteria that could lead to spoiled and dangerous meat. The IARC classifies nitrates and nitrites as "possibly carcinogenic to humans," because when meat containing them is fried or grilled at high temperatures, they can transform into N-nitroso compounds, like nitrosamines, which are known carcinogens.

Even if the nitrosamines aren't formed while your meat is frying, they could still be formed in your stomach. The acids in the stomach are enough to transform these preservatives into nitrosamines, too.

Studies on mice and rats have concluded that nitrosamines from meat may play a major role in the formation of bowel cancer, and observational studies in humans have found that people who consume more processed meat have higher rates of stomach, esophagus and bowel cancer, too.

Don't get fooled by packaging. Even "natural" or "organic" hot dogs—including ones that say "no nitrates or nitrites added"—can have nitrites at the same or higher levels than conventional brand hot dogs, The New York Times noted. That's often due to the addition of celery powder or celery juice as an alternative to synthetic nitrites. Celery is naturally high in nitrate, which, when treated with a bacterial culture, produces nitrite. While technically natural, that nitrite is virtually identical to the synthetic version.

Then there's the grilling problem. When organic matter like wood, coal or gasoline is burned, polycyclic aromatic hydrocarbons, or PAHs, are formed. Living near an incinerator or a highway can expose you to high levels of these carcinogenic compounds, but so can eating smoked, charred or barbecued meat.

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Studies reviewed by the European Union health agency found that the fattier the barbecued meat, the greater the PAH formation, because fat that dripped on the heat source would burn and in turn generate more PAHs, which adhere to the meat (in their study, researchers found "heavily barbecued lamb sausage" to be the worst of the worst). Among smoked meat, the length of time smoked and the type of wood used could increase production of PAHs–for example, burning hardwoods to smoke meat produced less PAH than softwoods due to their "higher smoke generation temperature." Poplar wood, considered a soft hardwood, was found to generate the most PAHs. Either way, you're getting a dose of compounds found to be highly carcinogenic to animals that ingest them.

And then you have the problem of heterocyclic amines (HCAs), a class of compounds found to promote cancer in animals. HCAs are formed in meat that is highly cooked, in high temperatures. Meat cooked above 300 degrees Fahrenheit (typical when you grill or pan fry a sausage, for example), or meats that are cooked for a long time tend to contain more HCAs, according to the National Cancer Institute.

While HCAs are formed in both processed and unprocessed meats, a comparative study found the highest levels in "well done and very well-done" oven-broiled bacon, a processed food.

Observational studies in humans have linked HCAs in meats and cancer rates. For example, researchers have found men who ate more well-done meat had higher rates of rectal and prostate cancers.

The National Cancer Institute suggests cooking meat away from an open flame and avoiding touching your meat to hot metal surfaces for too long, to cut down on HCA and PAH formation. If you must use a metal pan to cook your cancer-patty, at least flip it often, they say.

Or just try using a microwave instead, they say. It'll be fine, they say.

The meat lobby, of course, is having none of this. "They tortured the data to ensure a specific outcome," Betsy Booren, the North American Meat Institute's vice president of scientific affairs, told journalists regarding the IARC's decision on Monday.

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But according to the Global Burden of Disease Project, cited by the IARC in its report, diets high in processed meat could be responsible for 34,000 cancer deaths worldwide each year. That's compared to the estimated 600,000 people who die from alcohol-related cancers each year, and the 1 million who die from tobacco-related cancers, two other carcinogens that share the same designation as processed meats now do.