In a nutshell it is not the amount of calories people eat that make them fat but what they eat. The culprit is insulin which allows fat to be stored. But the insulin is created by carbohydrates so eating a diet high in carbohydrates causes a high insulin production which causes fat to be stored. Over eat carbs i.e. pizza, fries, burger buns you've got real problems. As have type 2 diabetics which is often caused by obesity are then given insulin as a treatment - a bit of a catch22 situation.
Join the movement and we'll start a revolution - stop all unnecessary shopping - seperate your needs from your wants.