Not high fat
One of the problems folks with CF have is that their pancreatic duct gets blocked.
This means that the fat-digesting enzymes from their pancreas
can't get to their gut and break down the fat they eat. A high-fat diet would be very bad in this situation. You need to have conversations with your CF doc to optimize your diet. You should have both a pulmonologist and a GI doc on your team.
Answer assisted by David Miller, Medical Student