Recently, the International Agency of Research into Cancer (IARC), a body affiliated with the World Health Organization (WHO) announced that red meat is “probably carcinogenic to humans” and that processed meat is “carcinogenic to humans.” These findings have been widely reported, with misleading headlines comparing eating meat to smoking in terms of cancer risk.
However, these headlines are entirely alarmist and rather off base, for two reasons.
Firstly, the IARC classifies things as carcinogenic based on the confidence in the evidence for a carcinogenic effect, and not on the magnitude of that effect. For example, the IARC would classify something as “carcinogenic” if a number of studies were in very good agreement and suggested an increase in cancer risk, even if the actual rise in cancer risk were quite small — say, one percent. Therefore, within the IARC’s “carcinogenic” category, things like smoking (high risk behavior) and eating processed meat (relatively low risk behavior) get inappropriately lumped together; consumers have no way of knowing based on the IARC’s classification scheme whether something that is “carcinogenic” is truly risky or not.
Professor David Philips, an expert in cancer risk at Cancer Research UK, has been quoted in the Cancer Research UK Science Blog saying that the “IARC does ‘hazard identification,’ not ‘risk assessment.’
Philips provides the analogy of banana skins. Banana skins certainly cause accidents, but banana peel slips and the resulting injuries are relatively rare. The injuries you would sustain also would not be too severe, in most cases: perhaps a bump or a bruise. Cars also cause accidents; obviously, these accidents pose a major risk of bodily harm. However, under the IARC hazard identification system, banana skins and cars would both be categorized the same, in a category called “causing accidents” — the frequency and severity of the accidents does not get taken into account.
Secondly, as alluded to earlier, the actual risk associated with eating processed meat is rather small, even if confidence in the data is very high. One of the really shocking findings reported by the IARC is that people who eat the most processed meat have a 17% greater chance of developing colorectal (bowel) cancer. That sounds really scary! But, it is important to remember the difference between a relative risk (17% greater) and absolute risk (the actual chance you have of developing a certain condition). For colorectal cancer, the baseline risk is something like 56 cases per 1000 individuals in those who eat the least amount of processed meat. For those who eat the most processed meat, a risk 17% higher means that 66 of every 1000 individuals will get colorectal cancer in this group.
Of course, people’s risk tolerances will vary, but I would not make sweeping changes in my diet based on such a small change in absolute risk. Keep in mind the risks are even lower for individuals who eat moderate amounts of red and processed meats — the 17% number only applies to those individuals who consumed the most processed meat. If you are consuming red meat and processed meat in moderation, it is likely perfectly safe for you to continue doing so. However, you should consult your doctor or a nutritionist before considering any major dietary change.