Inclusion: ≥6 years old with CF, taking ETI for at least 8 weeks prior to the study; Exclusion: Type I or type II diabetes, undergone organ transplantation, pregnancy, individuals taking insulin or glucose homeostasis medications, antibiotic use within 4 weeks of starting the study, hospitalization or steroid usage within 8 weeks of starting the study. The gene discussed is INS; the disease is cystic fibrosis.