[orwin]

It's probably due to genetics, their body assimilate food better than Caucasian, due to their diet for 5000 years being really light of fat and sugar, so when they follow the Caucasian diet (2300 cal a day high carbs high fat) it does not work.

Also, they are poor countries who can't produce the food they need for multiple reason (sometime it's population, but often it's mining/industrial pollution related) and they have to import the cheapest food available, ie leftover from US (and recently China) food processing.