Average Japanese diets are much healthier than American diets; there is less of a car culture, public transport is common. But do go on about fat shaming being effective.
The same can be said about most western Europe countries, yet they still have obesity rates above 20% compared to 4% in Japan.
https://en.wikipedia.org/wiki/List_of_countries_by_obesity_r...
>But do go on about fat shaming being effective.
It looks like the most likely explanation here.