Cystic fibrosis (CF) is a genetic disease with an autosomal recessive, chronic and progressive character about 10 to 25% of patients develop CF-related diabetes (DRFC). Until now, there is no evidence to support the use of low glycemic index diet to improve glycemic response in pre-diabetic and CF patients. The objective of this study is to evaluate the glycemic improvement after nutritional orientation in patients with cystic fibrosis.