I breastfed all my children until they were/are about two years old, except my oldest who was weaned at 8 months. For my cf children, I was unaware that they had cf during the time they were breastfed. My oldest (who is still PS) was always satisfied, so supplementation was never an issue. With Jacob and Juliette(who were said to be PS at the time of diagnosis, but are now PI), they were always hungry. I had planned to exclusively breastfeed, but by 5 months, Jacob was grabbing for the table food. In hindsight, I would have supplemented Jake and Juliette more, with breastfeeding being their main means of feeding. I think the breastfeeding was definitely vital to their health, and I thimk that supplementation would have given them that little extra edge.