Calorie counting is no fun at all. It is, however, important to consume 400 kcal less each day than you expend. Why? Imagine a sand dune; every day, the wind blows away a little bit of sand off the top. Adding the same amount of sand as is blown away each day will keep the dune at its original size despite the wind. Adding less sand than is blown away each day will make the dune shrink over time. The very same principle can be applied to calories. If you give your body less calories than it needs to do its job each day, it will start using up stored body fat.