I have been diabetic for about 18 years.
You need to talk with a good endo who also knows CF.
CF patients because we don't absorb fats and we are usually malnutrioned should not be cutting back on carbs or fats. You should be able to eat all the carbs you want ( sugars, starchs) and then you just dose yourself with insulin to cover it.
A nutrionist at the endo office should help you with this.
Try to exercise, drink lots of water. But it is important to eat well, and stay healthy. Some foods you think might not have carbs, do. Like pasta, bananas, potatoes, corn, beans. You can get a book on carb counting too. That will show you the breakdown. Eating out, especially at fast food places is killer with carbs. You will shoot through the roof, so you have to dose with insulin to compensate. Also pizza from take out places can be loaded. You don't realize how much sugar they put in these foods... makes people love it, and eat it.
Joanne Schum