Wednesday, 28 October 2015

How bad is having a bacon sandwich really?

Reading this week’s headlines warning us that eating bacon and sausages cause bowel cancer will probably turn you into a vegetarian instantly. But the way this message has been put forward is very misleading. The headlines are referring to a press release  of the International Agency for Research on Cancer (IARC) in which processed and cured meats like bacon are classified as group 1 carcinogens. The IARC reached that conclusion after carefully studying research which convinced them that there is a causal link between consuming these meats and bowel cancer. Eating 50 grams of processed meat a day will increase your risk of bowel cancer by 18%. To put things in perspective, group 1 carcinogens also include tobacco, alcohol, arsenic and asbestos, all known to cause certain cancers. So, is having a bacon sandwich as risky as smoking a cigarette or having a drink? Before diving into the interpretation of the outcome let’s first have a look at the research conducted.

It’s just an opinion

The above estimated risk increase originates from a meta-analysis of prospective studies on meat consumption in relation to bowel cancer published in 2011, it’s a “mashup” of research conducted in the past. In a prospective study a group of individuals with a meat rich diet is monitored over a period of time and compared to a control group that has a different diet (no meat, or to a much lesser extend). So, a relative risk is estimated. To have a like for like comparison between the two groups, as this is not a controlled experiment, the estimated relative risks are corrected with factors like age, BMI, alcohol consumption, sex, hypertension, diabetes, etc. As different studies probably correct for different factors and in different ways, it’s at least questionable whether the results from different studies can be compared. Are apples being compared to apples? More important however, there might be a factor not included in the corrections that explains why an individual eats more meat (red or cured) and develops bowel cancer. This is also known as confounding, which leads to spurious correlations. So, the IARC found that there is a positive correlation between meat consumption and bowel cancer, but can’t provide the proof that the relation is a causal one. It’s the opinion of the IARC.

Is eating bacon as risky as smoking?

What everybody should know is that the classifications of the IARC are based on strength of the evidence not on the degree of risk. So, two risk factors could be classified similarly even if one causes many more types of cancers than the other. Therefore bacon ends up in the same class as cigarettes and asbestos. These classifications are not meant to convey how dangerous something is, just how certain we are that something is dangerous. I can imagine that this way of communicating the risk is really confusing to anyone trying to work out how to lead a healthy life. CancerResearch UK is doing a much better job, by making explicit what the risks are. Clearly smoking is much riskier than eating a bacon sandwich.

Source : Cancer Research UK

Should you change your diet?

The IARC reports an 18% increased risk of getting bowel cancer when eating 50 grams of cured meat a day. But what does this mean? Increased risk compared to what? Clearly the missing information to know whether we should be worried about the increase in risk is how many people will get bowel cancer even if they don’t eat bacon sandwiches.  If there is a large risk, an 18% increase will be a lot worse than when the risk is small. The risk for an individual to get bowel cancer in the Netherlands is about 1 in 20, or 5%. It’s this risk of people getting bowel cancer that increases. So the risk becomes 5.9% instead a 5%. In absolute numbers, when 100 people eat a bacon sandwich every day, the number of people diagnosed with bowel cancer will increase from 5 to 6. So the 18% increase sounds a lot, but in absolute terms we should expect just one extra person to get bowel cancer. What do you think?  Will this stop you from eating bacon sandwiches? I’m not too fond of them, but with the above you should be able to decide if you want one. And in case you do, enjoy!