A reader sent me a link to an article about a rise in bowel cancer over the past 35 years. Let’s take a look:
Bowel cancer rates among men have soared by more than a quarter in the last 35 years, new figures have shown.
In contrast, women have experienced a rise of only 6 per cent, according to the report from Cancer Research UK.
Increasing rates of bowel cancer may be linked to obesity and diets high in red and processed meat and low in fibre.
You just knew as soon as you read that first paragraph that red meat would get the blame, didn’t you? I believe the reporter’s thinking process (if you can call it that) went something like this:
Hmmm, bowel cancer is on the rise. Well, we all know red meat causes bowel cancer, so it must be diets high in red meat that are the problem. Okay, off to write the story.
In the internet/search engine age, it takes perhaps two minutes to find out if people have been eating more red meat over the past 35 years. Here are some graphs based on USDA data. (Yes, the article is from the U.K., but I sincerely doubt food-consumption trends in the U.S. and U.K. are wildly different.)
Looks to me as if red meat consumption has gone down. We’ve been eating less cow meat since the mid-1970s – hey, that would be about 35 years ago, wouldn’t it? Pork consumption is about the same, but chicken consumption is way up. Perhaps we should blame the rise in bowel cancer on chicken.
But wait … I can think of another explanation. In a post last week, I linked to several studies suggesting that sugar feeds cancer. So let’s take a look at sugar consumption:
Red meat consumption has been dropping since the mid-1970s, but sugar consumption has gone up.
Is this proof that sugar is driving the rise in bowel cancer? Nope. Correlation does not prove causation. But when you have a negative correlation, it’s pretty strong evidence that there’s no causation. In other words, if I propose that drinking coffee causes obesity but then gather data showing that obesity has gone up while coffee consumption has gone down, I’d have to conclude that it’s extremely unlikely coffee causes obesity.
Suggesting red meat is causing the rise in bowel cancer was just a knee-jerk reaction by the reporter. It’s an opinion based on “everybody knows” evidence. He could have fact-checked that opinion without ever leaving his desk, and in less time than it took me to type this paragraph – but he didn’t. Sadly, this kind of intellectual laziness seems to run rampant among media health reporters.
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