Every body requires a different amount of daily caloric intake to function
properly. Your heart, lungs, kidney, brain and other internal organs require 1000-1400 calories a day to function while laying down. This is called you RMR-Resting Metabolic Rate. Your DCI - Daily Caloric Intake is what determines how many calories you require to do your other daily tasks. This will vary from person to person depending on your level of activities.
Now we all know that if we eat more calories than our DCI requires, our wonderful bodies will store that extra energy as fat. Well, we can thank Mother Nature for a few foods that actually burn more calories preparing, chewing and digesting them, than what is actually in them. I found a list of great negative calorie foods. With that said, you cannot survive on just eating these foods alone, so just try to add a few to each meal. See if you notice a difference.