Some observations... 1) Japan is not built around cars. There are more trains. You get to walk more. 2) Food portions are smaller, making it harder to overeat. 3) Fish is more popular than meat. Fish section in supermarkets is larger. Most kitchens have fish cooking equipment. 4) They do not put cheese in goddamn everything. I guess they get to eat more mercury (from fish) and arsenic (from rice).
I hear this a lot, but what does this really amount to? I live in a city without a car, and all my walking on my daily commute (during non-covid times) burns 125 calories or so. That's nothing. Eating two oreo cookies is more calories than that.
Moreover, consider that America is no more car centric than it was in 1970 or 1980, but people are much larger now than then.