While I agree with the point that the science of obesity is mostly crap, I'm not really sure that data given by this blog post is particularly conclusive.
An important fact to remember: many people lose weight at the end of their life.
Nonsensical argument based on mortality rates between teens and 30s, precisely before obesity-related health effects begin to kick in. What's truly terrifying, and mentioned not at all by TFA, is that we're seeing an uptick on when said health effects start showing up. That's the line people should be looking at, not some lackadaisical projection that everyone will be obese...and, oh my gods, athletes aren't on the curve and they're healthy, right?!? Very, very poorly reasoned.
Thought a similar thing - just comparing mortality rates by BMI seems very imprecise. All sorts of factors could come into play, like (making this up) teenagers tending to be less overweight than older people and a lot of teenagers dieing in car crashes. Or whatever - it is not even clear to me what the mortality rate is meant to be - deaths per year?
The irony is that LGM's analysis buys into using the BMI as the horribly blunt instrument it is, in just the same manner that he is criticizing.