Depends on your personal preference, that's all. Many people believed "heavy" was beautiful back in the 80s, and many still do today, in the US. So the "heavy" people, or you call the obese, have been breeding more in the US, thus ... heavy children.<quoted text>
As opposed the rampant obesity that you are so used too?
Dont know much about europe do you? Eastern european girls are often very pretty, probably for the last 50 years or so by far the higher proportion of worlds top fashion models have been eastern European and the majority of what is termed super models
In Europe the opposite trend was popular, and it seems it still is, thinner people are preferred, thus, thin people there breed more, resulting in more thin people.
It's very simple genetics and evolution.