Read this VERY, very informative article in Newsweek this month:
There is an alternative theory, one that has also been around for decades but that the establishment has largely ignored. This theory implicates specific foods—refined sugars and grains—because of their effect on the hormone insulin, which regulates fat accumulation. If this hormonal-defect hypothesis is true, not all calories are created equal, as the conventional wisdom holds. And if it is true, the problem is not only controlling our impulses, but also changing the entire American food economy and rewriting our beliefs about what constitutes a healthy diet.
Oddly, this nutrient-hormone-fat interaction is not particularly controversial. You can find it in medical textbooks as the explanation for why our fat cells get fat. But the anti-obesity establishment doesn’t take the next step: that fat fat cells lead to fat humans. In their eyes, yes, insulin regulates how much fat gets trapped in your fat cells, and the kinds of carbohydrates we eat today pretty much drive up your insulin levels. But, they conclude, while individual cells get fat that way, the reason an entire human gets fat has nothing to do with it. We’re just eating too much.
http://www.thedailybeast.com/newsweek/2012/05/06/why-the-campaign-to-stop-america-s-obesity-crisis-keeps-failing.html