A Meaty Subject…

Right.  Is it safe to come out yet?  I’ve spent the last week or so hiding in a Metaphorical bunker, to try and avoid the coming apocalypse.  The media are on high alert.  World leaders have made important public statements.  Whole countries are arming for war.  And all the time, Sausage shaped grenades have been going off left, right and centre……

World Health Organisation:  Processed meat causes cancer!

(Deep breath)  OK, here we go….

So, first of all, what is the source of the furore?  The International Agency for Research on Cancer (IARC), is part of WHO, the World Health Organisaion.  Last week, the IARC released a report which evaluated the risks of cancer, due to consumption of red and processed meats.  After reviewing the evidence, they came to the conclusion that red meat (eg. beef, lamb, pork) is “probably carcinogenic to humans” and that processed meat (eg. bacon, sausages, ham, salami) “is” carcinogenic to humans, as they found sufficient evidence that processed meat consumption caused colorectal cancer.

And….BOOM!  Next thing you know, everyone is shouting at once.  Austrian and German politicians publicly defend their sausages.  Argentinians “would rather die” than give up their steaks.  The press are having a field day….

So, what is the truth?  Well, first off, the main point I would make is that, again, we are talking about risk factors.  As I mentioned back in Just One Cornetto, the way that these stats are worked out is to look at exposure to certain factors (eg. tobacco, alcohol, asbestos etc.) and to see if the exposure correlates to incidence of cancer.  If it does correlate, then further research will attempt to determine if the exposure can be classified as a contributing factor.  That is what happened in previous investigations into the risks caused by exposure to eg. tobacco and asbestos, and it is also what has happened now, with processed meat.

Processed meat has now been identified as a risk factor for colorectal cancer.  According to the IARC report, daily consumption of a 50 gram portion of processed meat will increases the risk of colorectal cancer by 18%.  But the important thing to note is this: what does this statistic really mean?  What is the real risk of contracting colorectal cancer?  How does meat-eating change this!  And how does it compare to other, previously identified risks?

Now for tobacco, the risks are astronomical.  According to Cancer Research UK, exposure to tobacco (both by active smoking and passive tobacco smoke) is responsible for almost a fifth (19%) of all cancer cases in the UK each year, and causes more than a quarter (27%) of all cancer deaths.

Pretty nasty.  So what are the equivalent stats for processed meat.  Well, as stated above, processed meat increases the risk of colorectal cancer by 18%.  But this is what is called the relative risk.  The increase is relative to the original number, so if the original number is tiny, even a small increase can appear, in relative terms, to be huge.

Let me clarify this.  Let’s say that wearing tight jeans has been shown to increase the risk of a heart attack by 100%.  It hasn’t by the way!  I’ve totally made that up!  But let’s just say it has.  Now, you might think Yikes!  Tight jeans increases the risk by 100%!  But this statistic is meaningless if you don’t know the original numbers – you’ve nothing to relate it to!  So, you dig a little deeper and discover that the risk of a heart attack from wearing loose jeans is 1 in a million.  So, if you increase “1” by 100%, you get “2”, or 2 in a million.  So, the relative risk may indeed be 100%, but the absolute risk is only increased by an extra 1 in a million, or 0.0001%.

So, for the 18% relative risk associated with processed meat, we need to do the same thing – look at the actual numbers in order to work out the absolute risk.  And if you dig into the stats, you find that the overall risk of contracting colorectal cancer is 6.1% (ie. 61 cases per 1000 people).  And when you take meat eating into account,  those who consume little or no meat have a risk of contracting colorectal cancer of 5.6% (56 cases per 1000 people), while those who consume a lot of meat have a 6.6% chance of contracting colorectal cancer (66 cases per 1000 people).  So, 10 more high meat eaters will contract colorectal cancer than low meat eaters.  And 10 is roughly 18% of 56.  So, yes, the relative risk of processed meat-associated cancer is 18%, but the absolute risk is just 10 extra people per 1000, or an overall increase of 1%.

So in conclusion, yes, it’s true, eating lots of sausages bacon and pepperoni can increase your risks of colorectal cancer.  But not by much, overall.  And if you still want to give up bacon rolls, go ahead – all the more for me!

(Goes off to get a bacon roll…)

Bouvard, V., Loomis, D., Guyton, K., Grosse, Y., Ghissassi, F., Benbrahim-Tallaa, L., Guha, N., Mattock, H., & Straif, K. (2015). Carcinogenicity of consumption of red and processed meat The Lancet Oncology DOI: 10.1016/S1470-2045(15)00444-1

AG McCluskey (2015). A Meaty Subject… Zongo’s Cancer Diaries