You have of course heard the sad news about bacon. As the World Health Organization's International Agency for Research on Cancer put it Monday in a news release:
"The experts concluded that each 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by 18 percent."
How much is 50 grams of processed meat? In bacon terms it's about two slices. Just to be clear, it isn't that eating two pieces of bacon will increase your colorectal cancer risk by 18 percent. It's that eating two pieces of bacon every day for the rest of your life will.
But here's the important question that isn't directly addressed in the pages and pages of information released Monday by the IARC or in any of the subsequent news coverage that I read: What's the risk of colorectal cancer to begin with?
To illustrate how much this can matter: In 1995, the U.K.'s Committee on Safety in Medicines issued a warning that third- generation oral contraceptive pills increased the risk of thrombosis by 100 percent. What that meant was that the risk of getting thrombosis -- potentially life-threatening blood clots in the legs or lungs -- went from one in 7,000 for women taking second-generation birth control pills to two in 7,000 for those taking the third-generation variety.
Not a huge risk, then. But a 100 percent risk increase sounds quite ominous. As psychologist Gerd Gigerenzer describes in his book "Risk Savvy," the warning scared many women away from the pill. One result was an estimated 13,000 additional abortions the following year in England and Wales. Another was, ironically, a lot of thrombosis cases -- pregnancies and abortions are much more likely to bring on the condition than does taking a third-generation birth control pill.
Information about relative risk can be misleading, then, unless it's presented in the context of absolute risk.
So what's the absolute risk of getting colorectal cancer? To sum up tables from the National Cancer Institute, men men 60 and younger face almost 5 percent chance of getting colorectal cancer in their lifetimes, and a greater than 2 percent chance of dying from it. For women it's about 4.5 percent and 1.9 percent.
Colorectal cancer, then, is a relatively common and deadly disease. It tends to hit people later in life, when they're eventually going to die of something in any case. But still, it's worth trying to avoid. Let's say you're a man, you have about a 5 percent chance of eventually getting colorectal cancer, and you up your bacon consumption by two pieces a day. That increases your cancer risk to almost 6 percent -- not a trivial jump.
Unlike the ill-advised and since-revoked U.S. dietary recommendations against cholesterol, these processed-meat cancer-risk estimates are based on years and years of empirical research. The 18 percent figure comes from a 2011 meta-analysis, published in the open-source journal PLOS One, of nine different studies of colorectal cancer.
It's just an estimate, and it's always possible that other things that processed-meat eaters tend to do -- such as standing around grills full of burning charcoal -- raise their cancer risk.
Still, it wouldn't be unreasonable to make changes in your diet based on this evidence (and similar but weaker evidence on the link between red meat and cancer).
I like bacon a lot, but I'd rather have a five in 100 chance of getting colorectal cancer than a six in 100 chance. Good on the World Health Organization for getting the word out. What I don't understand, though, is why they didn't present the risks in those terms.
Contact Justin Fox, a Bloomberg View columnist writing about business, at firstname.lastname@example.org