Not the OP, but for all the people commenting below, I think what the OP means to say is that the body is a very complex system and calories from different sources absolutely do have different affects, on your ability to control fat storage and fat burning and to modulate your appetite. The laws of thermodynamics still hold - if you overeat it doesn't matter what you're eating, you will gain weight. But calories in calories out is so simplistic by comparison to reality, that it's a harmful way to look at things.