This study is about how different diets affect adults with cystic fibrosis (CF), a disease that affects the lungs and digestion. CF patients are at high risk for diabetes, especially a unique type called CF-related diabetes (CFRD). The study will see if the regular high-sugar, high-fat CF diet increases diabetes risk and fat around the belly organs, known as visceral fat. Sixty participants will be split into two groups: one with a low-sugar, high-fat diet and the other with a standard CF diet without sugar limits. All food for the 8 weeks study is provided. Participants will have 4 visits at the Emory Hospital to undergo tests, including an oral glucose tolerance test to check for diabetes and magnetic resonance imaging (MRI) to measure fat around the organs. Participants will be compensated for their time.

• Study duration is 8 weeks with all meals provided.
• Participants must attend 4 hospital visits for tests.
• Compensation is offered for participation.