> There's a couple of things in there that are just correlated to the fact that the author is around young/wealthy people, like the low obesity rate

The other issue is geographic - the author is a grad student in DC, which is one of the more fit areas of the country. This is one of the few cases where I'd say it's more a class thing than a wealth thing. Political staffers and the generic military types by and large, are not wealthy people, but are very scrupulous about avoiding obesity.