The beginning is a lot of water weight loss. Once you get past that then your body has to burn fat. Your calorie needs to be less than what your body actually needs, in so far as calories, fat, protein, carbs, water, sodium, macro minerals, nutrients, etc. Once you know exactly what your body needs, you can work with it. There is a science behind it for some people. Not everyone can just cut calories and drop. I speak from experience.