The food we consume everyday contains a certain amount of calories. These calories provide our body with the energy needed to do our daily activities. If we take less calories then our body will tend to use up the stored fats to meet the energy needs. The basic idea behind a low calorie diet is to reduce the number of calories taken in order to burn off the fats. This is the reason why many people who want to lose weight go on a low calorie diet trying to achieve fast weight loss.