What are potential cultural and economic factors lead to high obesity prevalence rate in the United States?

According to the country rankings 2010 regarding global prevalence of adult obesity (http://www.allcountries.org/ranks/global_prevalence_of_adult_obesity.html ), in 2010, the United States had the 18^th highest obesity prevalence rates among male and female adults. The total number of included country was 153 and the ranking of China was 136.  We can see the adult obesity prevalence was much higher in the United States than in China. What are the reasons that lead to such big difference? Comparisons between various aspects in America and in China would be helpful to interpret obesity rates disparity between two countries.  Besides significant genetic disparity, cultural and economic factors may also provide interesting explanations. For example, did the short lunch time (exposure) contribute to high obesity (disease; BMI≥30) rate in America? In China, the afternoon working schedule often starts from 1pm (in winter) or 2pm (in summer), so most people have 1.5-2.5 hour to have lunch and to have a rest. Sufficient lunch time allow people to eat healthy lunch in a relaxing way. While, in the United States, the lunch hour is relatively short. Oftentimes, people are pushed to finish the lunch rapidly in order to go back to office on time. The fast food, which contains high calories and fat, is favored by most Americans since it can save their time. Also, people may want to consume more calories at evening if they were dissatisfied with poor lunch. So, should we conduct a prospective cohort study to explore the link between lunch time and obesity? In this study, investigators can follow subjects with several years, and measure their lunch time and weight status. What about other possible factors besides the lunch time? Perhaps we can consider economic factors behind the fact. Let us think about the food market in China and in America. China is a low-income country and America is a high-income country, however, the food prices in these two countries are almost the same. This means most Chinese would have much concern about money when they purchase food, thus, Chinese may purchase less food than Americans do. Moreover, in China, vegetables and fruits are much cheaper and more available than meat and western fast food, so, Chinese may consume more vegetables and fruits to save more money. The food choice, which is closely related to weight status, could be driven by food market.

Reference:

1. http://www.allcountries.org/ranks/global_prevalence_of_adult_obesity.html