I have an op-ed on the new JAMA meta-analysis which concludes that a BMI between 25 and 35 correlates with a lower mortality risk than that observed among so-called normal weight people. (In America, the former group includes nearly 80% of everyone who public health authorities claim weigh too much).
I’m not under the illusion that a three-million person study authored by five distinguished senior scientists and published in the nation’s leading medical journal is going to actually cause anyone in a position of authority to reconsider anything — for reasons that I allude to in the piece, the actual data still have almost no effect on public policy in this area.
Still, it’s an encouraging sign that the obesity racket continues to be exposed as a product of an invidious combination of cultural obsession, and the economic interests that obsession generates.
A brief note on hazard ratios: Something that ought to tip off the skeptically-minded about the degree to which the focus on weight has nothing to do with mortality risk per se is just how minor the correlations observed in this area are. For example, it’s true that the fattest people in this study — those with a BMI of 35 and above — had a 29% higher mortality risk than the “normal weight” (sic) reference group. But what people tend not to take into account about these sorts of statistics is that, for most demographic groups, baseline mortality rates are extremely low, which means a few extra deaths will produce an impressive-sounding spike in relative risk.
For example, if you compare the risk that a 50-year-old man will die within the next five years to that of a 50-year-old woman, you’ll find that the man’s mortality risk is 71% higher. That sounds pretty bad, especially if you happen to be a 50-year-old man, but what this actually means is that the man has a 2.51% chance of dying over that five-year span, rather than a 1.47% chance. And note that this hazard ratio is nearly two and half times higher than that found among the very fattest people. So among the middle-aged, gender correlates far more powerfully with mortality risk than even the highest levels of “obesity.” (No word yet on what the government plans to do about the masculinity epidemic).
And of course we shouldn’t lose sight of the even more significant fact that we’re talking about correlations in observational studies, rather than any clinical demonstration of real causality. But when you can’t even demonstrate a correlation in the data for your thesis, you should probably reconsider it.