I think it's more likely diet rather than exercise that makes the difference. Can't outrun (or outwalk) a poor diet, and you can be a healthy bodyweight while eating "unhealthy" food and not exercising by just limiting the quantity you are eating.
I would argue that to be healthy you should exercise a reasonable amount and have some muscle rather than just being at a good weight. Gives you a stronger body, and helps your mental health (which Japan seems to struggle with).
I would argue that to be healthy you should exercise a reasonable amount and have some muscle rather than just being at a good weight. Gives you a stronger body, and helps your mental health (which Japan seems to struggle with).