Are you sure this isn't just an optical illusion? Maybe Americans look fat, because everyone else in the world is too thin. The solution might be for the rest of the planet to start eating fat Americans to kind of balance things out.
You can usually find vast, roaming herds of them at the local Mcdonalds, Burger King, or Wendy's fast food outlets. I suggest using a juicy Whopper sandwich as a special lure, or a Wendy's Triple for the difficult cases.
Have an American today! Its on us! :) Upvoted.
RE: Why Americans are so fat, a fun theory.