Last week the World Health Organization’s International Agency for Research on Cancer (IARC) announced that processed meat definitely causes colon cancer. Processed meat refers to meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavor or improve preservation. Most processed meats contain pork or beef, but processed meats may also contain other red meats, poultry, offal, or meat by-products such as blood. Examples of processed meat include bacon, hot dogs, ham, sausages, corned beef, and beef jerky as well as canned meat and meat-based preparations and sauces.
That’s right, bacon causes cancer. I should have known it after having dined in California a few years ago. Every restaurant we went to had prominent signs posted at the entrance; “WARNING: Chemicals known to the State of California to cause cancer, or birth defects or other reproductive harm may be present in foods or beverages sold or served here.” Not too stimulating to the appetite and probably overstated.
In addition, the IARC last week classified the consumption of red meat as probably carcinogenic to humans. All this led to some alarming but misleading headlines in the media, like this one from the Guardian last week; Processed meats rank alongside smoking as cancer causes – WHO.
Well, not quite. The IARC is an organization that evaluates the strength of evidence of existing research on the causes of cancer. In this particular analysis, published in the Lancet, a group of 22 scientists looked at 800 studies linking meat with cancer.
The IARC sorts hazards into 5 categories:
Group 1: carcinogenic to humans. Group 1 includes plutonium, smoking, alcohol, arsenic, asbestos, and now processed meat. Also sunlight and air (pollution).
Group 2A: probably carcinogenic to humans. 75 items are on this list including red meat, as well as shift work and working as a hairdresser or barber.
Group 2B: possibly carcinogenic to humans. 288 items are on this list including coffee, pickles, firefighting, dry cleaning and carpentry.
Group 3: not classifiable as to carcinogenicity in humans due to lack of data. This is by far the longest list.
Group 4: probably not carcinogenic to humans. There is only one substance in this group: Caprolactam, a component of nylon. So in a rare bit of good news, stockings are okay and in my medical opinion probably should be worn more.
Since some of my favorite things are on that list somewhere, I looked into what this study really means. First, it is important to understand that the IARC does hazard identification, not risk assessment. The IARC doesn’t evaluate how often something causes cancer, only whether it does so or not. The classifications are based on strength of evidence, not degree of risk. Two substances could be classified in the same category if one quadrupled the risk of cancer and the other increased it by a tiny amount. The classifications do not evaluate how dangerous something is, just how certain scientists are that something can cause cancer.
Take the case of bacon. The WHO has concluded that eating 50 grams of processed meat daily (two strips of bacon) increases the risk of colorectal cancer by 18 percent. That sounds bad. But that assumes you eat it every day for the rest of your life. More importantly, it is a relative increase in risk, not an absolute increase in risk. The lifetime risk for colon cancer for men in the U.S. is 5 percent. Eighteen percent of 5 is 0.9 percent; that is the amount your colon cancer risk may be increased by eating bacon. Any increase in risk is, of course, concerning, but the headlines may be overly alarming when viewed through the lens of the actual math. Colon cancer primarily strikes adults over 60, so the likelihood that you will die of something else anyway goes up.
Now take the case of smoking. Smoking increases your relative risk of cancer by 2,500 percent. So headlines such as “Bacon, burgers and sausages are as big a cancer threat as cigarettes, global health chiefs are to rule.”-Daily Mail, 22 October 2015, are wildly misleading. But they do sell papers.
Given the strength of evidence we have so far regarding processed meat and red meat and cancer, I do think it is reasonable to try and change our diets to reduce consumption of these foods. The health of the planet would improve as well since one of the major contributors to greenhouse gasses is the methane produced by beef cattle farming. But do this if you are really interested in reducing your risk of fatal colon cancer: get a colonoscopy at age 50. This could decrease your risk of colon cancer by as much as 50 percent. Now that is some good news.