Sugars are not going to weaken your immune system. When your glucose leves (blood suger) are out of control, you don't absorb nutrients on the molecular level. Over a period of time, this leads to malnutrition and that causes immune problems. Sugar is ok, but don't go overbord. Limit sweets, sodas which have empty calories. If you have a sweet tooth, eat ice cream, granola, drink chocolate milk...these all have good calories and fat. Fructose, the sugar in fruit, is wonderful and healthy.Debbie 22 yr old w/ CF, CFRD