It's a combination of nature and nurture, I think.
The genetic 'spread-out', so to speak, is similar, at least within people of the same 'race'. Yet some nations (most notably the US) have a much larger percentage of obese people.
Obese people like to blame genes, and in some cases, that's justified. In most, it's about taking in more energy than you burn. And of course, a matter of what kind of energy, in the form of food, one gets.