So the only thing you can think of to explain this is cultural factor?
You don't think genetics could be a factor here at all?
You don't think genetics could be a factor here at all?
Although for a thoughtful and thorough analysis:
An introductory wikipedia article: https://en.wikipedia.org/wiki/Epidemiology_of_obesity
Google scholar search: https://scholar.google.com/scholar?q=epidemiological+obesity