You will surely lose some weight with the HCG diet, but this is not going to be only fat loss. Besides, it is one unhealthy way of dieting, and you won't be able to do it for a long time. However, diets should be considered as a way of life - you can not just run a diet for a couple of months, and expect not to get back the lost weight once you return to your old nutrition that made you gain fat. Diet is about a lifestyle - a way of living all the way, not just for some months. Therefore, you should choose a well balanced diet that will cover all the needs of your body, such as Carb Cycling mentioned above - it is very easy to follow, and yet it is very effective.