There's also a different culture towards cooking. It's often easier and cheaper to eat out in the US than it is in Europe. I think in Europe, or at least in Belgium, most families cook their own meals every day. Because you go out and buy the individual ingredients, you usually end up with a much healthier diet. In terms of diet my favorite place to live would probably be southern Europe, especially because you can eat decent food at low prices at local restaurants (which is impossible in Belgium).
I wouldn't necessarily say you have more food in general. Some stores in the US are fantastic, but there are a lot that make it impossible to buy healthy food too.
The weirdest thing I've noted however is how vegetables and fruit taste differently in the US. I have no explanation for this at all.