A recent report concluding that if you eat processed meat (bacon, sausages and suchlike) you’re more likely to get cancer in your pancreas has attracted predictably wide media coverage. More surprisingly, the reports I noticed (BBC News, Sky News and Guardian) were fairly reasonable accounts, quoting the main figures, the source of the information (British Journal of Cancer) and one or two ‘expert’ comments thereon. Usually science reporting in the ‘media’ is more feel than fact and appears to be motivated by coming up with eye-catching headlines rather than precise explanations (being precise, there is a Bacon Eaters Warned Of Deadly Cancer Risk in the above – but let’s not be too critical).
What the papers didn’t say
What such reports almost always fail to mention – and these were no exception – is how devilishly difficult it is to do surveys linking what we eat to what happens to our bodies. One method is to get a group of people with a given disease and ask them what they’ve eaten over the last umpty months/years/decades. You don’t need to be a stats wizard to see the major problem with this! Alternatively, so-called ‘prospective studies’ start with healthy individuals who are followed for exposure to potential factors and subsequent development of disease. Exposed and unexposed sub-groups are compared for disease rates. There are huge problems with these studies too, not the least being that you have no real idea how well the punters stick to the rules – in this case, what they eat.
The predictable upshot over many years has been that, apart from fruit and veg (good anti-cancer stuff, as we all know), for pretty well every survey showing something we eat gives us cancer there’s another that says it either has no effect or it’s actually protective.
Much easier than actually doing either type of survey is to do what these processed meaters did: put together all the sensible studies you can find (in this case eleven prospective surveys between 1966 and 2011) and see if a clear message emerges. Though not perhaps evident at first sight, this is actually quite a useful thing to do because by lumping all the data together you get a large number of patients and controls and the hope is that, out of the confusion of multiple smaller surveys, clarity will come forth.
And, up to a point, it did. The relative risk of pancreatic cancer emerged as 1.19 if you eat 50 g of processed meat every day (it would be 1.00 if you take The World Cancer Research Fund’s advice and avoid the stuff altogether). And, of course, the risk goes up the more of it you eat.
How scary is that?
So where does that leave us and how scared should we be by the scary headline? Have I been unwittingly irresponsible indulging a life-long taste for bacon, sausages and such like? Mmm…bacon…Mmm…sausages. (Sorry – Homeric moment there). Well, something like a 20% risk increase may be significant but it isn’t huge. Then 50 g is a fair wodge of bacon or whatever to eat every day. What’s more, the authors admitted that they’d had to make a few assumptions about just how much processed meat people actually had eaten in the various studies they collated, because some only listed ‘servings’ or ‘times’. Then there’s the question of how is the deed done if processed meat does drive cancer? The study authors noted that the most likely culprit is preservatives commonly added to such food – because these can indirectly cause DNA mutations. Having just salivated round the wondrous display of meats, hams, bacons, sausages etc. in my local Farm Shop (Gog Magog Hills: don’t miss it if you’re anywhere near Cambridge) I note than none of their stuff contains additives or preservatives. Whew!!
And the bottom line…
So my advice to me is: don’t panic, don’t pig out – but do keep an eye on where piggy bits come from. All of which is not to minimise the threat of pancreatic cancer. It’s the eighth biggest cancer killer worldwide, nearly 8,000 Brits died from it in 2008 and there’s no effective treatment. What’s the best thing to do – or not to do? Well, as we’ve said, take it easy on the bacon butties. But two things are strongly associated with pancreatic cancer: smoking (contributes to 20% of cases) and obesity. Not smoking’s easy, of course. Now, how to avoid getting fat…
Larsson, S.C. and Wolk, A. (2012). Red and processed meat consumption and risk of pancreatic cancer: meta-analysis of prospective studies. British Journal of Cancer advance online publication 12 January 2012; doi: 10.1038/bjc.2011.585.