There are other contributing factors as well, intrinsically linked to the evolving social/economics dynamics in our society. For example, it's now much more common for families to have two working parents, and thus less time to prepare nutritionally complete food from scratch. So people naturally gravitate toward engineered food which is easier to prepare, but less "good" as food. There are many other similar effects that lead to Americans eating more/poorer food like advertising, school lunches, etc, but the deck is definitely stacked against this world to reverse the obesity epidemic.