I can tell you that if there's nothing wrong with you except fat it is easy to get thin. You eat and drink the same as always, only half. If you are handed a plate of food, leave half; if you have to help yourself, take half. After a while, if you are a perfectionist, you can consume half of that again ... On the question of will-power, if that is a factor, you should think of will-power as something that never exists in the present tense, only in the future and the past. At one moment you have decided to do or refrain from an action and the next moment you have already done or refrained; it is the only way to deal with will-power.