Sugar, usually in the form of HFCS is added to almost any processed food these days, to make it more delicious and to make the food more profitable. HFCS is very, very cheap to produce. You're eating more sugar without perhaps even knowing you are. Low fat foods, introduced in the late 70's have the same amount of calories, but sugar was added to make the food more palatable.
Sugary items, like sodas, are also coming in larger portions, as well.
Sugars from fruit are less of a problem, as the fruit also contains fiber, which slows down the absorption of the fructose, and helps to not overload your liver.
Calories in the form of glucose are digested differently than fructose or HFCS - the latter two which are processed in your liver. You shouldn't worry about eating too much bread - you should be looking at if the bread contains added sugar.
Good video to watch:
Fruit?
I'd put my money on a relation between abundance of food plus obesity because too high calorie intake is the main culprit of obesity.
From Wikipedia.
Sugar has been around far longer than our very recent obesity epidemic.
One point to make from the article, though: "They suggested that the physician-authors were trying to con the obese with the fraudulent argument that they could become lean without doing the hard work of curbing their perverted appetites."
If you want to really confuse what's going on, turn to moralism. Desire to judge and to avoid being judged completely messes with incentives and people will line up to the "hard working" side while avoiding the "lazy" side, regardless of what is actually true.