> For example, do you think the US has an obesity problem and Japan doesn't because, by pure chance, there are far more people who "choose" to eat unhealthy in the US?

Yeah a good example is when a family member visited the USA and sent me a picture of their food that they got at a restaurant. It was a downtown restaurant in one of the 20 largest US cities. I was stunned as it was easily 30% more than a food portion you would get in our home country of Germany. In the country I am currently residing in, with BMI scores somewhere between Germany and Japan, you are usually getting 30% less on your plate.

So defaults definitely skew you into one particular direction. But there are also often stronger nudges than just large portions at restaurants. I have heard from friends from rural USA that while their home village is surrounded farmland it's still a food desert because the farms are 100% cash crops and you can't transport vegetables that far economically. Apparently this is the case for many parts of the rural USA. On the other hand, back when people in the USA got excited about gold they would build infrastructure in no time. Just check the pictures how quickly say SF grew. If people got similarly excited about eating healthily, you might find good food even in these remote places.

So yes, it's easier to live in a society where a lot of people have your own lifestyle, than to live in a society where you live a lifestyle different from that of normal society.