The killing game

Posted on October 27, 2015

After yesterday's announcement by the World Health Organisation that processed meat is a definite cause of cancer in humans and that red meat is a 'probable' cause, there has been something of a backlash from scientists trying to put the whole thing into perspective.

For example, Suzi Gage in the Guardian blamed 'simplistic reporting' for equating the risk of processed and meat with smoking. 'The WHO have deemed the strength of evidence that processed meats cause cancer to be equivalent to that showing that smoking causes cancer. This means that if you eat a lot of red or processed meats you are increasing your risk of cancer. But to compare it to something as lethal as smoking is confusing and dangerous.'

Over on the Cancer Research UK science blog Casey Dunlop emphasises the difference between relative risk and absolute risk. 'The results showed that those who ate the most processed meat had around a 17 per cent higher risk of developing bowel cancer, compared to those who ate the least.' She notes that for people who eat the least processed meat the absolute risk is 5.6 per cent, but for the people who ate the most it's about 6.6 per cent. Foregoing bacon, sausages and the rest to avoid an increased risk of one percentage point might seem, so the implication goes, unnecessarily drastic.

Comparing the risks of processed meat with active smoking seems alarmist, then. But the figures being bandied about for the risks from processed meat are much the same as those being quoted for passive smoking in the run-up to the introduction of smoking bans. Take this from a report by the US surgeon general in 2004: 'The pooled evidence indicates a 20 to 30 percent increase in the risk of lung cancer from secondhand smoke exposure associated with living with a smoker.'

And just as with the evidence for meat, there were plenty of confounding factors to call into question such a small effect. As the BMJ noted, also in 2004, 'The considerable problems with measurement imprecision, confounding, and the small predicted excess risks limit the degree to which conventional observational epidemiology can address the effects of exposure to environmental tobacco smoke.'

But, by and large, the kind of scientists who are now berating the media for 'simplistic reporting' were silent about the weakness of the evidence on passive smoking. Organisations like Cancer Research continue to trumpet the risks of 'secondhand' smoke despite the feeble conclusions of research on the matter. The consequence was a draconian and comprehensive ban on smoking in workplaces and enclosed spaces, regardless of the wishes of business owners or their customers.

It seems that politics, not statistics, is the decisive factor in such 'myth-busting' commentary. And it's also understandable why consumers should react badly to their food being labelled 'carcinogenic' – because they know that bans, regulations and taxes may soon follow.