November 2, 2015
Last week there was good news and bad news linking health risks to meat consumption. The good news is that the media want to tell people about which foods might cause cancer, and some reporters are skilled at communicating the data. The bad news is that the International Agency of Research into Cancer (IARC), an arm of the World Health Organization, does a poor job of putting data into context, and that, in turn, leads to alarmist reporting by less responsible members of the media.
Early last week the IARC published a report about the risks of consuming meat, especially processed meats like bacon and hot dogs. For years, researchers around the world have been investigating and talking about the health risks that accompany the consumption of red meat and processed meats, from heart disease to colon cancer—the IARC’s report does not contain new information, per se. Rather, it frames the data from a specifically cancer-oriented perspective. The IARC’s big news this week is that it has classified processed meat as a carcinogen and red meat as a probable carcinogen.
Immediately, headlines screamed about how bacon is the new smoking. This is not accurate, but it is “news you can use” if you’re trying to satisfy the general public with instructions about what to eat.
After the flutter of scary headlines, the more sober science writers go to work putting things in context. Andrew Revkin, writing in The New York Times’s Dot Earth blog, does a great job rounding up the responsible reporting, especially by The Atlantic and Vox. One of the themes in The Atlantic story is the difference between degree of risk and strength of evidence. In risk assessment, we study degree of risk, or, how dangerous something is. In hazard identification, we study how much evidence there is to support a claim of something being dangerous (but not necessarily how dangerous it is).
The IARC report does a good job of hazard identification, addressing strength of evidence, meaning that there are many forms of evidence that support the hypothesis that consumption of processed meat is a risk factor for cancer. In other words, the IARC’s “carcinogen” classification doesn’t really tell us how dangerous processed meats are; rather, it tells us that the scientists who wrote the report are very certain that processed meats, are to some degree, carcinogenic.
For nine years I worked with the U.S. Preventive Services Task Force, and my job included many hours of discussing the difference between quality of evidence, magnitude of effect, and clinical significance of a particular risk factor or benefit from something such as screening, counseling, vaccine, or chemoprophylaxis. While there, we assessed quality of evidence: Grade I was assigned to data from well designed and executed randomized clinical trials, the gold standard; Grade II was for data from cohort or case-control studies and time series studies; Grade III was designated for expert opinion in the absence of reliable data from studies. This kind of rating system would be a good start for the IARC in terms of how they grade the hazard identification. As for communicating risk assessment, that’s another bag of worms entirely.
It’s unfortunate that the agency’s lack of communication effectiveness has to tarnish what is, at heart, important research. There is more than enough evidence to support the hypothesis that anyone who eats a lot of meat should eat less in order to be more healthy. In addition to the personal health advantages of eating less meat, there is a world of other good reasons to eat less meat, all supported by the Meatless Monday Campaign: by reducing meat consumption, we might be able to slow down deforestation, which could keep our planet cooler longer by preserving carbon sinks and avoiding the release of nitrous oxide, a potent GHG (greenhouse gas); with less livestock production we create less methane, another potent GHG, on the farm; and by being choosier about what kind of meat we eat when we do eat meat, we increase the likelihood that food animals will be treated humanely and raised without the misuse of antibiotics.
We’re always going to get the “Bacon is the New Cigarette” stories and the “Woman Lives to 102, Says She Eats Bacon Every Day” stories. Those are the extremes. Somewhere in the middle lies the truth, which is that for every 1,000 worldwide cancer deaths related to tobacco there are 34 cancer deaths attributable to eating processed meat. The take home message from the WHO report is that red meat and processed meat are not foods that make you healthier, and that what our planet needs is to reduce meat consumption.