There’s a chance they’re overweight.
That American characteristic of being ever on-the-go results in a lot of unhealthy food being consumed in an effort to save time. This is just part of the reason the United States has the highest obesity rate in the world—32.2% for men and 35.5% for women.
While 66% of American men and women are either obese or overweight, that same statistic is just 37% for the rest of the world. This isn’t to say that spotting an overweight person abroad means they’re American, but it does say the odds are in their favor.