
This is a question many immigrants ask since the food in the US is not only different; it also has a lot of hidden fats. In Austria, we are used to eat the visible fat on meat - most Americans feel disgusted just by the thought of it. We also use butter on sandwiches. Still, I believe our diet in Austria has been less fat-saturated than here.
In the first months after our arrival, I gained a couple of pounds because I just didn't realize how many calories are in a burger or in a slice of pizza. Since I returned to daily cooking, mostly Austrian dishes, the pounds are gone.
If you also wonder, what to eat and what to avoid - there is a great article on yahoo about take-out food. Don't miss it: http://food.yahoo.com/blog/editorspicks/7112/make-take-out-healthier-dishes-to-order-and-avoid