Why BMI is Bloody Mindless Idiocy

I've posted the odd critique of the obsession on the part of public health officials with BMI (here, here, and here for example), but in case you're not persuaded, here's Paul Campos to set you straight:

A particularly clear example of this is provided by the Harvard School of Public Health, which for many years has been pushing a phony claim with great success. The story is simple: That it's well-established scientific fact that being "overweight" — that is, having a body mass index figure of between 25 and 30 — is, in the words of Harvard professors Walter Willett and Meir Stampfer, "a major contributor to morbidity and mortality." This claim has been put forward over and over again by various members of the School of Public Health's faculty, with little or no qualification. According to this line of argument, there's simply no real scientific dispute about the "fact" that average-height women who weigh between 146 and a 174 pounds, and average-height men who weigh between 175 and 209 pounds, are putting their lives and health at risk. Furthermore, according to Willett, such people should try to reduce their weights toward the low end of the government-approved "normal" BMI range of 18.5 to 24.9 (the low end of the range is 108 and 129 pounds for women and men respectively).

It's difficult to exaggerate the extent to which the actual scientific evidence fails to support any of this. In fact, the current evidence suggests that what the Harvard crew is saying is not merely false, but closer to the precise opposite of the truth. For the most part, the so-called "overweight" BMI range doesn't even correlate with overall increased health risk. Indeed "overweight," so-called, often correlates with the lowest mortality rates. (This has led to much chin-scratching over the "paradox" of why "overweight" people often have better average life expectancy and overall health than "normal weight" people. The solution suggested by Occam's Razor — that these definitions make no sense — rarely occurs to those who puzzle over this conundrum). Furthermore, it's simply not known if high weight increases overall health risk, or is merely a marker for factors, most notably low socio-economic status, which clearly do cause ill health.