While there is some correlation between wealth and obesity (it's hard to overeat if you literally can't afford food), correlating being first world and obesity problems is a bad idea. Just look at this map, as you can see America is somewhat of an exception, with most mega fat nations being second rate at best.  https://cdn1.sph.harvard.edu/wp-content/uploads/sites/56/2012/10/global-obesity-map-2008-medium.jpg