The US population probably isn't much different from the rest of the world, in that regard. What's different about them is they live in the US. Drop foreigners

The US population probably isn't much different from the rest of the world, in that regard. What's different about them is they live in the US. Drop foreigners from skinnier countries in the US, and, as a cohort, they'll gain plenty of weight (as with lifelong Americans, some individuals will buck the trend, of course) It's a complex social-environmental, economic, and political problem.