Our pilot studies using once-daily Levemir in children with CFID1 and 2 found that this simple insulin regimen (rather than multiple daily injections) was well accepted by patients, with minimal hypoglycaemia, and resulted in significant weight gain and improved lung function (compared with 12 months prior to insulin). Sample size calculations for the CF-IDEA Trial are based on our pilot studies. When 70-80% of patients have completed the protocol, the study statistician will perform an interim analysis (blinded to the other investigators) to check the original power calculations.