For the purposes of this discussion, I will take your numbers as truth and run with it.

Are you arguing that 1:5 is good, but 1:4 is bad?

The only large populations of people in the world that aren't quite fat are southeast Asians. And this is fairly accurate whether they leave in southeast Asia or in the US or western Europe. Not 1:5, closer to 1:20 or in one case 1:50.

Even then, southeast Asian obesity rates are climbing. The US may have led the pack because of a consistently high standard of living, but I don't see any indication that there are macroscale populations anywhere in the world keeping the disease at bay.