Why are Europeans generally thinner than the Americans?

In two words, diet and exercise. European cultures prize quality over quantity. You can see this is in a lot of immigrant populations, actually- the first generation who moves to the US still eats their traditional, healthy foods, but their kids eat american junk food, and are usually much heavier than their parents. As for exercise- America is a big place. You can walk around an American suburb- you need a car to go anywhere. Europe is much more crowded, more people live in cities or small towns where you can walk from place to place, and Europeans do not work as many hours as Americans, so they have more time to be active.