Ok sorry for the stereotype, I figured there wasn't enough space to put many words. I meant "In developed countries, why do poor people tend to be fat compared to general population and rich people tend to be thin?"
Yes, I've heard of the so-called "cheap calories" you can get from junk food. Also, stress slows down your metabolism and you may be more stressful when faced with finacial uncertainties.
However, I can think of other factors which could suggest why rich should be fatter, intuitively speaking.
Rich people tend to have jobs that require less manual labour while low paying jobs tend to have more manual labour.
Rich people can afford to have a few cars per family and everyone drives everywhere without having to walk much.
Yes, rich people can afford to pay for fitness programs but less face it, some middle-aged people are too lazy to go on a fitness program even when they can afford it anyway. Also, everyone tends to have junk food ocassionally even when they can afford healthier foods.
So I guess less stress and good nutrition overrides other factors such as exercise?