First, I am not a register dietician. However, this is actually something I know quite a bit about as I am an exercise science major. The KEY to losing weight is calories in vs. calories out. Everything I've studies (research journals, scientific articles, course lectures, physiology textbooks, sports nutrition (taught by a registered dietician and nutrition PhD, etc.) says this. In essence, if you take in (eat) more calories than you burn, your body is in a caloric surplus and will store the excess energy. This is mostly stored as fat unless you are only in a 300-500 kcal surplus and are participating in a resistance training program. If you burn more calories than you take in, then your body must make up this difference by using some of its stored energy (fat or adipose tissue) to carry on basic functioning and metabolic processes. Many usually ask the question: "Why can I just not eat and then loose all the fat I want?" This is a terrible way to loose weight!!!! This puts your body in starvation mode. When your body is in starvation mode it uses just about everything it can for energy. Since muscle tissue is more easily converted to energy than fat, it will use a greater portion of muscle tissue first. So, if you starve yourself you will loose weight. However, alot of it will be muscle tissue and not fat. You will end up weaker but at a light weight, usually with a greater body fat percentage because you now have less lean tissue relative to fat mass. The KEY is to eat about 500 Kcals less than you burn so your body won't go into starvation mode. Doing it this way will make your body use a much higher percentage of stored fat because it is not in a crisis situation. So remember, kcals in vs. kcals out, withing moderation. This is the key to loosing BODY FAT and not just weight.