I have the opposite problem and don't have CF, but annoyingly enough, I have advice anyway 
Although my husband and I tend toward skinny, we are the runts of our families and have observed the struggles of siblings and parents. And we want to avoid struggles for out kids, who haven't necessarily inherited our genes. (Let me clarify though, I never ever tell them how much to eat...only what to eat.) So here is my advice. If you already do this stuff, then ignore it
Entirely avoid certain aisles of the grocery store. If you can do the perimeter of the store only, you will lose weight by the effort of cooking alone: fresh fruits and veggies, potatoes, BEANS, rice, pasta, oatmeal, and meats. That stuff in the middle is convenience fluff (except for pasta sauce and whole grain cereals, and maybe some other stuff that I am not thinking of). BUT, don't forget to buy healthy treats: dried fruit, chocolate, nuts, honey for tea/toast. These things satisfy cravings but are not empty calories.
Do not fall into the diet soda trap. It is garbage. The containers hurt the Earth and it does nothing for you. Plus, someone is always doing a study about how it might mess us your ability to regulate your appetite.
Probiotics (obvious for those of us on abs a lot). S. Boulardi is one to look for.
If you do this stuff, plus your awesome exercise routine, and don't lose weight, then I would think that your body is best suited for the weight it is currently at.
Good luck!
Edited to add "Beans"--very important for non-fat protein.
Also, if you can get into foreign food, that may help too. I cook a lot of rice and beans (not the refried kind) and Thai food. The herbs and spices make me happy and it is not so hard. I buy a tiny jar of green curry paste, add fish sauce, a can of coconut milk, brown sugar, veggies and chicken or fish. Serve over rice. YUM.
Although my husband and I tend toward skinny, we are the runts of our families and have observed the struggles of siblings and parents. And we want to avoid struggles for out kids, who haven't necessarily inherited our genes. (Let me clarify though, I never ever tell them how much to eat...only what to eat.) So here is my advice. If you already do this stuff, then ignore it Entirely avoid certain aisles of the grocery store. If you can do the perimeter of the store only, you will lose weight by the effort of cooking alone: fresh fruits and veggies, potatoes, BEANS, rice, pasta, oatmeal, and meats. That stuff in the middle is convenience fluff (except for pasta sauce and whole grain cereals, and maybe some other stuff that I am not thinking of). BUT, don't forget to buy healthy treats: dried fruit, chocolate, nuts, honey for tea/toast. These things satisfy cravings but are not empty calories.
Do not fall into the diet soda trap. It is garbage. The containers hurt the Earth and it does nothing for you. Plus, someone is always doing a study about how it might mess us your ability to regulate your appetite.
Probiotics (obvious for those of us on abs a lot). S. Boulardi is one to look for.
If you do this stuff, plus your awesome exercise routine, and don't lose weight, then I would think that your body is best suited for the weight it is currently at.
Good luck!
Edited to add "Beans"--very important for non-fat protein.
Also, if you can get into foreign food, that may help too. I cook a lot of rice and beans (not the refried kind) and Thai food. The herbs and spices make me happy and it is not so hard. I buy a tiny jar of green curry paste, add fish sauce, a can of coconut milk, brown sugar, veggies and chicken or fish. Serve over rice. YUM.