“Red meat blamed for 1 in 10 early deaths,” blared the Drudge Report last week. The linked news article referred to a study by Harvard scientists finding that unprocessed red meat and processed meat like bacon and hot dogs are linked to a higher risk of mortality.
So is meat a big killer? Hardly. For those familiar with the phrase “the latest study,” it’s another opportunity to learn whether these studies are as reliable as they seem. (It won’t require too much math, I promise.)
Consider, for example, that the data in this study comes from a questionnaire mailed out once every 2 years to a sample of people asking them about the kinds of foods they ate. I don’t know about you, but I have a hard enough time remembering what I ate last week, much less what I was eating last July.
The authors also noted: “Men and women with higher intake of red meat were less likely to be physically active and were more likely to be current smokers, to drink alcohol, and to have a higher body mass index.” Now, the authors did try to control for this mathematically — but when there are three times as many smokers at the high-red-meat-consumption end than at the low-consumption end, that’s a pretty significant confounder.
Further, consider the conclusion that red meat increases the risk of dying by 10 to 20 percent. Anything less than a 100% increased risk — a relative risk of 2 — can be considered pretty weak, according to experts. According to the National Cancer Institute, “Relative risks of less than 2 are considered small and are usually difficult to interpret. Such increases may be due to chance, statistical bias, or the effect of confounding factors that are sometimes not evident.”
Remember that the link between smoking and cancer was enormous — a several thousand percent increased risk. That’s truly significant. Ten percent, not so much.
That’s relative risk. The absolute risk is another matter — my risk of getting colon cancer in any given year could be, say, 1 in 10,000 if I don’t eat red meat. If I eat red meat, and it becomes 1.2 in 10,000, I hope you’ll understand if I don’t drop my BLT and make a beeline for the nearest ER.
All this doesn’t even consider publication bias. Researchers recently writing in the International Journal of Obesity reported that studies on the link between sugary drinks and obesity suffered from “white hat bias.” In other words, research finding a link between soft drinks and weight gain were more likely to be accepted for publication than those that found no such link.
Still with me? It’s incredibly hard to legitimately prove much of anything with a study, or even a handful of studies, that are conducted observationally.