The Guardian wins today's award for misleading science reporting. "Bacon, sausages and ham rank alongside smoking as causes of cancer," their headline thunders, and technically that's true. About as true as saying that my housecats "rank alongside" elephants as large mammals.
In other words, size matters, not just taxonomy. So what does the World Health Organization really say? This is from their handy Q&A:
About 34 000 cancer deaths per year worldwide are attributable to diets high in processed meat....These numbers contrast with about 1 million cancer deaths per year globally due to tobacco smoking, 600 000 per year due to alcohol consumption, and more than 200 000 per year due to air pollution.
The consumption of processed meat was associated with small increases in the risk of cancer in the studies reviewed....An analysis of data from 10 studies estimated that every 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by about 18%.
In other words, the WHO took care to explicitly say that processed meat didn't rank alongside smoking when it comes to cancer risk.
Colorectal cancer is fairly common as cancers go, but it still affects only about 4.5 percent of the population. What's more, an increase of "18 percent" does not mean your cancer risk skyrockets from 4.5 percent to 22.5 percent. It means that if you eat a few ounces of processed meat—bacon, bratwurst, ballpark franks, spam1—every day, your lifetime risk of getting colorectal cancer goes up from 4.5 percent to 5.3 percent.
That's not nothing. You're probably better off taking it easy on the spam. Nevertheless, not everything in the category "causes cancer" is created equal. If you're really worried about cancer, cut out the smoking, the drinking, the overeating, and the city living. Once you've done that, then it's time to decide if you also want to skip the bacon.
1But not hamburger, despite what the Guardian's photo editor seems to think.