I think this is mostly a social/societal thing - at an early age in schools they tell kids that they should only eat until they're 80% full. And there's substantial social pressure and bullying of anyone considered even mildly overweight.

Also, most people have a lot of walking/biking built into their daily schedule, especially in larger cities where having a car is impractical.

This all means that while there is a huge amount of sweets and fatty food, it's usually eaten in moderation, and people get exercise in their daily lives to work it off.

The public school food system also encourages healthy eating, and also general societal responsibility since children are the ones responsible for serving and cleaning up. https://www.youtube.com/watch?v=fze5s1SlqB8&t=1188s&pp=ygUsZ...