America is not fat. The scale used to determine whether or not one is fat is severely screwed up. Even some Olympians are considered obese. (no they are not sumo wrestlers)
Yes, the BMI is inaccurate, especially in special cases like weightlifters. But most peoplee with a BMI of 30+ are not weightlifters.
But saying America is not fat only because the BMI is inaccurate doesn't hold water, since in most studies countries are compared between each other. In order to compare you have to make the same analysis with the same measure method. And in all these studies America is on top of the fat scale. So even if not absolutely so, America is surely relatively fat.