By Caitlin Dow, PhD
If you’ve spent any time on the internet in the last couple of months, you’ve likely heard about the recent statement on red and processed meat from the World Health Organization (WHO).The statement was produced by a Working Group of 22 scientists who gathered together at the International Agency for Research on Cancer (IARC), with the goal of considering all data from over 800 epidemiological studies on red and processed meat in order to determine their potential carcinogenicity. The group defines red meat as “mammalian muscle meat – such as beef, veal, pork, lamb, mutton, horse, or goat” and processed meat as “meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation” (1). Based on the available data, the Working Group concluded that “that there is sufficient evidence in human beings for the carcinogenicity of the consumption of processed meat.” And then the internet exploded. But what exactly does this mean?
The IARC is responsible for categorizing chemical compounds based on the strength of evidence that said chemical may be carcinogenic. In this statement, they categorized processed meat as a Group 1 carcinogen and red meat as a Group 2B carcinogen.These categorizations are used to describe the strength of evidence that these compounds may be carcinogens; thus, Group 1 is used to distinguish “established carcinogens” [e.g. acetaldehyde (a metabolite of alcohol), oral contraceptives, formaldehyde, and sawdust], whereas Group 2B includes compounds that are considered “possible carcinogens” [e.g. benzofuran (a compound in coal tar), butylated hydroxyanisole (an additive found in foods, cosmetics, rubber, etc.)] (2).And while these classifications are important, they are easily misconstrued, as was the case in this statement by the IARC. These classifications simply tell us that a compound could be hazardous to human health. What they don’t tell us is degree of risk.That’s important because lots of things can be hazardous without posing a significant risk.For example, UV radiation is a hazard, but it is only a risk if one is exposed to excessive amounts of UV radiation.That is, risk is the product of hazard multiplied by exposure. Reduce your exposure, reduce your risk. That’s where most people got confused with this IARC statement.
The media jumped on the statement and let out a warcry against red and processed meats.But what most of them failed to mention is the all-important question: how much red and processed meat need be consumed to increase risk for developing cancer? One meta-analysis found that risk of colorectal cancer increased with increasing intake of red and processed meats up to 140 g/day (~5 oz/day) (3). Further, risk of developing colon cancer in response to consuming red/processed meat increases by ~25% for every additional 100g consumed/day. Thus, this study was evaluating risk in consumers who eat A LOT of red and processed meats.Importantly, these effects were strongest in European (29% elevated risk/100 g/day increase in intake) compared to North American (11% elevated risk/100 g/day increase in intake) and especially to Asia-Pacific studies that observed a non-significantly reduced risk (6% reduced risk/100 g/day increase in intake). These results indicate that not all populations are equally affected, which is likely due to differences in genetics and/or lifestyle. And what about people who don’t even eat red/processed meat everyday? Are they at risk just by eating these foods once in awhile? A meta-analysis by Norat, et al. (4) estimated that reducing red meat consumption to 70 g/week (~one 3 oz. serving/week) would reduce colorectal cancer rates by 7-24% in regions with high intake.That is, eating red or processed meat once a week likely does not increase risk for colorectal cancer.
At the end of the day, the IARC added processed and red meat to their list of carcinogens.But in terms of translating that into a public health message, they didn’t do a great job.Yes, red and processed meats are hazards to health. If you choose to eat them, keep your exposure low and your risk will likely also be low. As always, eat a varied diet, high in fruits and vegetables, whole grains, legumes, nuts and seeds to ensure high antioxidant and anti-inflammatory compound intake to protect against potential damage that red and processed meats may pose.
1.Bouvard, et al. on behalf of the International Agency for Research on Cancer Monograph Working Group.Carcinogenicity of consumption of red and processed meat. Lancet: Oncology. 2015 Dec;16(16):1599-1600.
2.American Cancer Society. Known and Probably Human Carginogens. https://www.cancer.org/cancer/cancercauses/othercarcinogens/generalinformationaboutcarcinogens/known-and-probable-human-carcinogens. 2015 Oct.
3.Chan DS, et al. Red and Processed Meat and Colorectal Cancer Incidence: Meta-Analysis of Prospective Studies. PLoS One. 2011;6(6):e20456.
4.Norat T, et al. Meat consumption and colorectal cancer risk: dose-response meta-analysis of epidemiological studies. Int J Cancer. 2002 Mar;98(2):241-56.