The World Health Organization International Agency for Research on Cancer (IARC) issued a report in late October claiming processed meat causes cancer. IARC reviewed epidemiological studies and decided to classify the consumption of processed meat as “carcinogenic to humans” and consumption of red meat as “probably carcinogenic to humans”.
IARC did not do any new research. It reviewed approximately 800 epidemiological studies on cancer relating to red and processed meat.
One story written by the Canadian Broadcasting Company stated “…it isn’t clear on what products [processed meat] that includes.” The CBC noted that processed meat may also contain poultry. In fact, the CBC claims “Processed poultry accounts for 40% of processed meat sold worldwide.”
The researchers said there was an association between eating red and processed meat with colorectal cancer. The IARC press release indicates “Current evidence supports approximately a 15 to 20% increased risk of cancers of the colon and/or rectum per 100 g of red meat or 50 g of processed meat consumed per day” (An ounce = 28.3 grams).
It also might have been helpful if news reports had advised individuals that radiation, alcohol, tobacco, and obesity are also risk factors for bowel cancer.
The press release issued by IARC on October 26, 2015, advises that 22 experts from 10 countries reviewed approximately 800 studies and said “…based on limited evidence that the consumption of red meat causes cancer in humans and strong mechanistic supporting a carcinogenic effect.” The news media, from what I heard, did not make clear that consumption of processed meat creates a small risk. In fact, one IARC researcher said, “For an individual, the risk of developing colorectal cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed.” IARC also said “Red meat contains high biological-value proteins and important micronutrients such as B vitamins, iron…, and zinc.”
This study is based on epidemiology. There are a number of problems in relying on such a study. “Epidemiology is concerned with the incidence of disease in populations and does not address the question of the cause of an individual’s disease. This question, sometimes referred to as specific causation, is beyond the domain of the science of epidemiology.”(Reference Guide on Epidemiology, National Research Council, 2011). Georgia Ede M.D. states “There are many types of studies researchers can conduct to try to understand the world around us, and the epidemiology study is the weakest, least reliable method available.” In fact, another study entitled “The Problems with Some Epidemiological Studies” states that if studies are not evaluated and interpreted with care, they may result in more harm than good.
The IARC Monograph released on October 26, 2015, qualified the study but you never read about the qualifications. For example, the report evaluated whether high temperature cooking methods of meat create a cancer problem. IARC’s answer is that such cooking “…may contribute to carcinogenic risk but [cooking methods] is not yet fully understood.”
As to the issue of which type of red meat is safer, IARC said “…there is not enough information to say whether higher or lower cancer risks are related to eating any particular type of red meat or processed meat.
Another interesting question was comparing the risk of eating red meat versus eating processed meat. IARC declares, “Consumption of red meat has not been established as a cause of cancer…” I suspect this nuanced answer escaped most news outlets.
After setting forth the number of cancer deaths per year worldwide based on diets high on processed meat, IARC suggested 34,000 cancer death per year worldwide are attributable in diets high in processed meats, but in comparison there are 600,000 cancer deaths per year due to alcohol consumption and approximately 1 million cancer deaths globally due to tobacco smoking.
With all the media attention about the risks of red meat and processed meat, IARC says on page three of its paper on the carcinogenicity of red and processed meat that “…eating processed meat causes colorectal cancer. An association with stomach cancer was also seen but the evidence was not conclusive.”
It is extremely important to understand that the IARC study is evaluating epidemiological data. No doubt epidemiological studies and data are helpful but as one writer said, “Epidemiologists are complacent about methodology, and…epidemiologists encourage over interpretation of epidemiologic data by the public.”
(This article first ran in Farm Futures on November 3, 2015)