While there are fat people from all walks of life I feel that fattness is becoming an epidemic amongst people in lower income brackets. The cheaper options for food and snacks are full of fake sweeteners and overly processed garbage that your body is not meant to process. If you're poor and buying the cheapest food and snacks at walmart you're filling up on all of that crap that your body will have a hard time burning off. Not to mention, I feel that a lot of diseases are linked to these chemically laden foods. Anything ingredient in your food that you can't pronounce, is probably killing you.
As we move up the socioeconomic ladder people are a little more aware of their health and can afford better products. Not to mention if you're well off you probably have time to jog, ride a bike or play a sport. Unfortunately for the less affluent folks, they are more likely to spend their "free time" working a 2nd or 3rd job so they don't loose their home. As a result they don't have the time to worry about their health and what they are eating. They're going to pop a micowave dinner in for there kids and get to their next job.
So as you can see, it is my opinion that America's growing disproportionate distribution of wealth is partly to blame, well that, and fat fatties who just want to eat