http://www.newsweek.com/why-pizza-so-good-978590

If you find donuts, pizza and cheeseburgers difficult to resist, your flimsy willpower isn't necessarily to blame as a study has found our brains are programed to crave the double-whammy of carbohydrates and fats. 

When we are faced with foods both high in fat and carbohydrates, like many processed foods are, the part of the brain in charge of processing reward is kicked into a higher gear when compared with foods high in one or the other, according to a team of researchers in the U.S., Germany, Switzerland, and Canada.