Glucose Metabolism in Cystic Fibrosis Related Diabetes (CFRD)

Inclusion Criteria: * Individuals who have at least one copy of the F508 deletion and are on ETI medications and individuals who have a different mutation and are not eligible for ETI medications * Age 21-75 years at time of consent * BMI 19-50 kg/m2 (In Asians BMI is \~ 2 points lower for comparison so it is 17-48 kg/m2) * Creatinine ≤ 1.4 mg/dl in women and ≤ 1.5 mg/dl in men * HbA1c ≤ 11% lifestyle treatment or mono/combination therapy with oral hypoglycemic agents (e.g. metformin or sulphonylurea or SGLT2i) and/or insulin. * Willing to be at a stable weight for duration of the study. * An understanding of and willingness to follow the protocol and sign the informed consent Exclusion Criteria: * Debilitating chronic disease * Anemia \<10 gm/dL in females and \<11.0 gm/dL in males * Symptoms of undiagnosed illness on history/exam * Abuse of alcohol or recreational drugs * Pregnancy * Active hepatic disease * Current use of the following drugs and supplements: corticosteroids, benzodiazepines, opiates, barbiturates, anticoagulant therapy * Any other medication that the investigator believes is a contraindication to the subject's participation