I lived in Japan for two years. Not a large metropolis like Tokyo but a mere 45 minute train ride to the NE, a modern planned city full of research institutions, had the feel of a wealthy US suburb. It was a car based city, you basically drove to work, but there was ample room for those who wanted to walk or ride bikes in most areas.
One thing I noticed, the young generation (18-22 something) had become either big boned or borderline obese (i.e. both kinds) just like in America. Not everyone, but it was surprisingly common.
I attribute it to ample access to fast food (McD's, Pizza Hut, KFC, 7-eleven, high availability of western style deserts and pastries, etc...).
I had a terrible eating habit then, still mostly western style. The only reason I think I didn't gain weight tremendously is that things were still a bit healthier there food wise and I had much more walking activity. Once I moved to another country (SEAsia) for a few years, things went down hill fast - no way I was walking around in the heat