There aren’t many foods that have the cultural appeal of bacon. Whether it’s being plastered everywhere online, or served on a BLT in your local cafe, something about bacon has captured the attention of people around the world. It might have a bit to do about a very successful marketing campaign by Sigmund Freud’s nephew (yes, actually), it might be because we’ve idealized this cured meat as the peak of delectability.
Of course, it might just be that bacon is delicious.
But, according to news from across the world, bacon isn’t the savior that we thought it was. No, bacon — and all preserved meats, in fact — are actually killing you from the inside. It turns out that eating bacon gives you a 20% increased risk of bowel cancer, which, if you’re like me and enjoy bacon but don’t like cancer, sounds pretty damn terrifying.
Thankfully for all of us, the headlines were wrong. You can get back to your butties.
Bacon probably isn’t giving you cancer.
The recent study that has everyone writing meaningless meat headlines was another Big Scary Study. I’ve written about these before — basically, the idea is that you take a very large group of people, test them for issues, and it’s even scarier because so many people were involved.
That’s not really how statistics work, but we run with it anyway.
This Big Scary Study took 500,000 people in the UK, asked them questions about their diet, and then followed up an average of 6 years later. At follow-up, people who ate the highest amount of red and preserved meats were at a 20% increased risk of getting colorectal — bowel — cancer, compared to people who ate very little/none. This was equivalent to eating about 76 grams of red and preserved meat a day, or ~3 rashers of bacon.
Hence the headlines.
The scientists in the study also controlled for a range of factors to try and ensure that the result reflected the truth. What this means is that they took into account things like age, weight, and education, which we know from previous research can have an impact on who gets bowel cancer. They accounted for all the factors they knew about in the study’s statistical model, meaning that it’s unlikely that these had an impact on the outcome.
So the study showed that more bacon meant more cancer. But before you run screaming from your full English, it’s worth noting that there’s more to the story.
The first big problem with the way that this study was reported is a fairly simple issue: relative vs absolute risk. It’s something that most people find very easy to understand, but can completely change how you think about research.
The basic idea is that relative risk is the risk ratio — the chance of one thing happening divided by the chance of another thing happening. Absolute risk is the risk difference — the chance of one thing happening subtracted from the other thing.
So let’s look at what happened in this study. There were 68,359 people who ate the lowest amount of bacon, and of these 274 got cancer. There were 192600 people who ate the highest amount of meat, and of these 1209 got cancer. That makes the rates 274/68359 = 0.4% and 1209/192600 = 0.6%
Based on those figures:
Relative risk = 0.006/0.004 = 1.5 = 50% increased risk of cancer
Absolute risk = 0.006–0.004 = 0.002 = 0.2% increased risk of cancer
We could say that there was a 50% increased risk of cancer — or, in the adjusted model (remember all those confounders?), a 20% increased risk — but we know that there are issues with this. It’s true, but doesn’t really communicate the real risk to individuals. It’s much better to communicate the risk using the absolute value, i.e. that there was an 0.2% increased risk of colorectal cancer for eating an extra 3 rashers of bacon per day.
Not nearly as scary when I put it like that, is it?
To put it another way, about 4 people out of every 1,000 get bowel cancer. In a group of people who eat more than triple the normal amount of red and preserved meat, 6 out of 1,000 will get bowel cancer.
Much less scary, but much more meaningful.
There were other issues with interpreting the study. It didn’t establish causality — we can control for the confounders that we know about, a bit harder for the ones we don’t/can’t measure — and it was done mostly in middle-aged white people in the UK. It’s possible that this result was an artifact of social factors, and even if it wasn’t, it only really applies to white people in the UK.
But really, the biggest issue was that the risk was wildly overblown considering how complex this all is.
Which brings us to the headlines. Yes, they were technically correct, but I think we can all agree that “KILLER RASHER: Pack of bacon a week increases risk of bowel cancer by a fifth” doesn’t really communicate the risk in a meaningful way.
Science is hard. Epidemiology is a complex field and communicating risk can be extremely difficult. More importantly, we’ve built a media system that rewards sensationalism, and doesn’t condemn misrepresentations, which means that the best way to earn money as a publisher is to churn out nonsense. The only way to really change that is for all of us, everywhere, to question what lies behind the headlines, and actually read some of the research we hear about in the news.
It might be hard, but at least we’ll know what’s really happening.
The media was wrong. We should probably cut back on bacon — it’s a calorie-dense food, and generally speaking not great for your health — but realistically the risk that it will give you, the person reading this article, cancer is very slight.
Don’t worry too much about the headlines.
There are worse things than an extra rasher of bacon in the morning.
You can now listen to Gid on the Sensationalist Science podcast: