The “body mass index” gauge of obesity is easy to calculate, but that very same simplicity means it has some obvious limitations as a metric. Still, it seems to me that it’s a very useful one and much of the criticism misguided for reasons that Monica Lastnameunknowntome explains well at Feministe:
Here’s my response: of course it is. It’s an index. This is what indexes do, they aggregate individual pieces of information to tell you something about a whole. The BMI was never intended to be used as a measure of personal health, but was instead meant to tell us something about entire populations. It’s usefulness on that score remains intact: you can broadly say that, if America’s BMI average is increasing, Americans are getting fatter. Unless it can be explained by something else, like a population-wide protein-shake/weight-training-routine frenzy, which is unlikely to happen.
Similarly, these international comparisons of BMI are telling us something meaningful:
It’s simply not the case that very-high BMI is so much more common in the United States than in France because Americans are all incredibly muscular compared to French people. Admittedly, it would be nice to have more sophisticated information on this subject, but public health is an important subject and it’s necessary to draw some conclusions based on available data.