&#62; There is no real "secret". Its simple mathematics.<p>It's math but it is definitely not simple math. Both overeating and undereating lead to adaptations and those adaptations can be very different in different people and different conditions, for example stress levels and macronutrients. Those adaptations can affect the body as well as the mind (through perceived energy levels). And body and mind are intertwined in a way you cannot ignore.<p>Ultimately there is a delta calorie equation that is simple, but it's as useless and trite as saying that a pregnant woman gains weight because she eats more calories than her body burns. It's trivially true, but misses the most important levels.