Cystic fibrosis is an autosomal recessive inherited disease linked to various mutations in the gene coding for the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein, with respiratory and digestive disorders conditioning the prognosis. Digestive damage may be responsible for malnutrition of multifactorial origin (insufficient energy intake, increased energy losses, increased basal metabolic rate), and studies show a correlation between reduced lean body mass and respiratory function. In 2019, the French National Authority for Health (HAS) redefined undernutrition by including quantified reduction in muscle mass and/or function as a phenotypic diagnostic criterion. Elexacaftor-Tezacaftor-Ivacaftor, an innovative therapy (authorization in 2021) for this population, aims to restore the function of CFTR protein. Significant improvements in lung function and weight gain were observed from the first weeks of treatment. These improvements have also led to the emergence of lesser-known nutritional problems in these patients, such as overweight and the development of metabolic complications. Nonetheless, new management options in terms of dietary adjustments and adapted physical activity for these patients are possible, given the development of their abilities. Adapted Physical Activity (APA) helps to improve general muscular function by strengthening respiratory and skeletal muscles, improving aerobic capacity, and aiding bronchial drainage through muscle strengthening and endurance work. Maintaining or even increasing muscle mass depends not only on appropriate food intake and optimal dietary management, but also on regular physical activity, as recommended by the HAS. Our hypothesis is therefore that a structured dietetic/adapted physical activity program (DIAPASOM program) can increase the percentage of lean body mass at 12 months in adult cystic fibrosis patients treated with Elexacaftor-Tezacaftor-Ivacaftor.