> Skinnier countries aren't skinnier because the people there have more willpower, it seems, but because they live in a skinnier country and are surrounded by the culture, laws, physical layouts of the created world, et c., that come with that.

Do we have data on that?

I guess you could look at natural experiments, like people who lost and won H1B lotteries, and see if only the ones actually making it to the US get fat?