Actually, obesity is more related to poverty and poor eating habits derived from low-income or low-SES.
>why is america fat
Obesity is huge among poor class of Americans, among white trash and negros. While theiro obesity rate among middle to high classes of society is lower than most European countries.
In USA you have very rich people and very poor people. There's a huge social and economical gap there.
Hell, even between middle class and upper class there is an astronomical gap.