The goal of the study extension is to see whether the incretin hormone GIP increases insulin secretion in individuals with CF and normal glucose tolerance compared to individuals without CF and normal glucose tolerance. This study includes 3 or 4 visits.

The purpose of this research study is to examine and understand the various mechanisms that contribute to CFRD and gain a better understanding of potential means to treat CFRD. Participation will include 2-3 visits, home monitoring, and will last about 2 years.