On Monday, the World Health Organization’s International Agency for Research on Cancer officially classified processed meats as carcinogens. The study, published in Lancet Oncology, concluded that eating foods like bacon, hot dogs, and sausages causes colorectal cancer. How they cause cancer is less clear, but the existing science offers some explanations.

Cancer Research UK points out that heme, a component of blood (and therefore more likely to be found in any meat than, say, a carrot), seems to be broken down by our bodies into cancer-causing “N-nitroso” compounds.

But the fact that red meat was classified as “probably” carcinogenic while the verdict on processed meat came without a qualifier suggests that the latter’s increased cancer-causing qualities stem from processing itself. According to the IARC, this includes meat transformation via “salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation.”

A classic pastrami sandwich is viewed at Katz's Delicatessen in New York City.

There’s no shortage of studies pointing toward nitrates as carcinogenic culprits. These preservatives, which are also found in cheap red wine, are responsible for Spam’s pink glow and five-year shelf life. They also generate the aforementioned N-nitroso compounds, as explained by a 2011 meta-analysis linking processed meat and cancer published in PloS One:

“Nitrites or nitrates added to meat for preservation could increase exogenous exposure to nitrosamines, N-nitroso compounds, and their precursors; meats cured with nitrite have the same effect as fresh red meat on endogenous nitrosation.”

When N-nitroso compounds damage the cells lining the gut, neighboring cells go into replication overdrive in an attempt to replace them. Any situation where cells rapidly duplicate is an opportunity for genome replication to go wrong — which is how DNA accumulates the mutations that cause cancer in the first place.

Smoked foods also fall under the IARC’s processed meat umbrella. Barbecuing or grilling food at high heat is already thought to produce carcinogenic compounds like heterocyclic amines and polycyclic aromatic hydrocarbons (which, incidentally, are also found in cigarette smoke). The process of smoking meats is thought to do the same.

International Green Week Agricultural Trade Fair

The science has a long way to go before finding conclusive evidence of the actual cancer-causing mechanisms at play. Still, the IARC’s analysis of over 800 papers at least did a thorough job of identifying the likelihood that certain foods are carcinogenic, based on the existing data. According to the report, this morning’s breakfast of bacon and eggs probably won’t kill you, but it wouldn’t hurt to indulge less often.


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