CFers tend to be more prone to easy weight loss. Many people who have respiratory issues will. For example if someone that doesnt have CF develops pneumonia, they will probably lose some weight. The difference is that with CFers that weight loss is as critical as the meds we take. A body needs "fighting power" when dealing with issues within it. If a CFers body loses too much weight then it doesnt have the stamina to fight as hard. We dont absorb our nutrition as well or as easy and most of us are fighting some type of bug at any given time or just burning calories with the coughing & exertions from treatments. Our bodies never get the proper "no calorie burning rest" it should. This combination of things is what causes weight loss in CFers.