As you probably know, a calorie is a unit that measures the energy content of the food that you eat. On average, women need to eat about 2000 calories per day while men need 2500 (obviously, this depends on metabolic health, age, height, weight, activity levels etc.). If more calories leave your body than enter it, then you lose weight. But randomly cutting calories without any regard to your diet is not a sustainable way to lose weight. In order to maintain a calorie deficit we recommend a few lifestyle changes.