As you probably already heard, earlier this week the International Agency for Research on Cancer (IARC), which is the World Health Organization’s (WHO) cancer agency, categorized processed meat as “carcinogenic” and unprocessed red meat as “probably carcinogenic.”1 What you might not have heard is that in an accompanying Q&A document, the IARC also said, “Eating meat has known health benefits.”2
Those who read the IARC’s statement and its Q&A document are likely to conclude that this story is nowhere near as dramatic and consequential as headlines from The Guardian, The New York Times, and other news outlets have implied:
- “Processed meats rank alongside smoking as cancer causes – WHO” – The Guardian3
- “Meat Is Linked to Higher Cancer Risk, W.H.O. Report Finds” – The New York Times4
Let’s see what the IARC actually said, then put things in context so we can determine what it means. The IARC evaluates chemicals, pollutants, biological agents, and other substances so as to determine whether or not they are carcinogenic. Agents are classified into one of several groups, ranging from “Group 1: the agent is carcinogenic to humans,” to “Group 4: the agent is probably not carcinogenic to humans.” The IARC does not determine how much any particular agent actually increases one’s risk of getting cancer. In its own words, the IARC explains,
“The classification indicates the weight of the evidence as to whether an agent is capable of causing cancer (technically called “hazard”), but it does not measure the likelihood that cancer will occur (technically called “risk”) as a result of exposure to the agent.”5
This is an essential point. Processed meats are now grouped into the same category as cigarettes and asbestos, but this doesn’t mean the risks associated with processed meats are anywhere near those of the latter two. Cigarette smoking, for example, increases one’s relative risk of getting lung cancer by 2,500%.6 Eating processed meat, according to the IARC, increases one’s risk of getting colorectal cancer by an estimated 18%.7 Given the frequency of colorectal cancer, this means that eating 50 grams of bacon every day over the course of your life would increase your risk of getting cancer from 5% to 6%.
Missing the Big Meaty Picture
Of course, all this talk of risk misses a bigger point – context is essential. For example, will those who smoke while eating healthy diets have the same chronic disease risks as those who smoke while eating unhealthy diets? Probably not. Red meat consumed within the context of a health-supportive Paleo diet is healthy. On the other hand, red meat consumed within the context of a junk-food diet might not be healthy, especially regarding poor-quality meat.
Dr. Cordain points out, “observational studies and even randomized controlled trials typically do not control for a variety of additional elements found in feedlot-raised red meats” and “only in the past 200 years of so have we ever consumed domesticated animals fed grains, injected with hormones, antibiotics, exposed to heavy metals and pesticides and sequestered in feedlots by the hundreds of thousands.” So when someone says meat is unhealthy, we should remember that meat is not a commodity; it ranges from poor to superior quality.
The Problem with Observational Studies
To assess carcinogenicity, the IARC analyzes observational studies. As Dr. Cordain and others have repeatedly pointed out, such studies alone cannot demonstrate causality. In response to the IARC announcement, Dr. Cordain noted, “In order to establish cause and effect between diet and disease, it takes more than just observational epidemiological evidence. There must also be what is referred to as ‘biological plausibility’ in which evidence gathered from tissue, animal and short-term human metabolic studies support causality.”8, 9
With respect to unprocessed red meat, the IARC’s “probably carcinogenic” determination is not even based on strong epidemiological evidence. It’s based on “limited evidence,” which according to the IARC, “means that a positive association has been observed between exposure to the agent and cancer but that other explanations for the observations (technically termed chance, bias, or confounding) could not be ruled out.”10
So the next time your vegetarian co-worker tells you that red meat causes cancer, remember the following four rebuttals:
- The IARC’s classification is based on observational studies, which cannot show causality.
- Evidence that unprocessed red meat could be carcinogenic is based on “limited evidence,” which means confounding factors could not be ruled out.
- The magnitude of risk for eating processed meat (and red meat if causality could be demonstrated) is nowhere near that of established risky behaviors, like smoking.
- Context matters – high-quality meat is healthy within the context of healthy diets, which include plenty of vegetables and other healthy foods.
Despite all the fanfare about increased cancer risk, at least the IARC acknowledges, “Eating meat has known health benefits.” It wouldn’t have been sensational, but this should have been the headline used by major news organizations.
1. World Health Organization, IARC. (October 26, 2015). IARC Monographs evaluate consumption of red meat and processed meat. Press Release Number 240. Retrieved from http://www.iarc.fr/en/media-centre/pr/2015/pdfs/pr240_E.pdf
2. World Health Organization, IARC. Q&A on the carcinogenicity of the consumption of red meat and processed meat. Retrieved from http://www.iarc.fr/en/media-centre/iarcnews/pdf/Monographs-Q&A_Vol114.pdf
3. Boseley, S. (October 26, 2015). Processed meats rank alongside smoking as cancer causes – WHO. The Guardian. Retrieved from http://www.theguardian.com/society/2015/oct/26/bacon-ham-sausages-processed-meats-cancer-risk-smoking-says-who
4. O’Connor, A. (October 26, 2015). Meat Is Linked to Higher Cancer Risk, W.H.O. Report Finds. The New York Times. Retrieved from http://www.nytimes.com/2015/10/27/health/report-links-some-types-of-cancer-with-processed-or-red-meat.html
5. World Health Organization, IARC. Q&A on the carcinogenicity of the consumption of red meat and processed meat. Retrieved from http://www.iarc.fr/en/media-centre/iarcnews/pdf/Monographs-Q&A_Vol114.pdf
6. U.S. Department of Health and Human Services. (2014). The Health Consequences of Smoking—50 Years of Progress: A Report of the Surgeon General. Atlanta: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2014.
7. World Health Organization, IARC. Q&A on the carcinogenicity of the consumption of red meat and processed meat. Retrieved from http://www.iarc.fr/en/media-centre/iarcnews/pdf/Monographs-Q&A_Vol114.pdf
8. Flegal KM. (June 1999). Evaluating epidemiologic evidence of the effects of food and nutrient exposures. Am J Clin Nutr, 69(6):1339S-1344S.
9. Potischman N, Weed DL. (June 1999). Causal criteria in nutritional epidemiology. Am J Clin Nutr, 69(6):1309S-1314S.
10. World Health Organization, IARC. Q&A on the carcinogenicity of the consumption of red meat and processed meat. Retrieved from http://www.iarc.fr/en/media-centre/iarcnews/pdf/Monographs-Q&A_Vol114.pdf