I bought food at a supermarket in China for the first time yesterday. Granted, I probably went to one of the most expensive supermarkets, at a Japanese department store near Jing An Temple, but it's really interesting to see food economics working essentially as they "should" for health. The lower down the food chain, the cheaper the food. For example, a whole bag of this reddish/green spinach-like vegetable cost 5 yuan (less than $1). But 6oz of beef cost about 50. "Organic" (the meaning of this word is questionable here) tomatoes cost about 12-15 yuan for three large tomatoes, which I'd consider pretty cheap, and "bottom-feeder" fish are cheaper than top-feeders like salmon, tuna, etc. Even outside the supermarket, you can see some of the effects. KFC is considered an upper-middle class luxury food, and one chicken sandwich there costs the same as a good meal for two or three people at a mid-range local Chinese restaurant.
Maybe this is why there are way fewer overweight people here compared to America.