The aim of the study is to describe the evolution of caloric intake in patients with cystic fibrosis with an indication to start treatment with Elexacaftor/Tezacaftor/Ivacaftor according to the Marketing Authorization, between the start of treatment and at 12 months.

Cystic fibrosis is a genetic pathology linked to a dysfunction of the CFTR protein.

Undernutrition is common in the natural course of cystic fibrosis, it is linked to exocrine pancreatic insufficiency but also to the increase in energy expenditure due to respiratory damage.

At a time when these CFTR modulators are greatly modifying the prognosis and management of cystic fibrosis, it is important to describe how caloric and nutritional intake evolve under treatment with Elexacaftor/Tezacaftor/Ivacaftor in order to be able, in the long term, to adapt nutritional recommendations under treatment with CFTR modulators.

The aim of the study is to describe the evolution of caloric intake in patients with cystic fibrosis with an indication to start treatment with Elexacaftor/Tezacaftor/Ivacaftor according to the Marketing Authorization, between the start of treatment and at 12 months.

Inclusion Criteria:

• Patient with cystic fibrosis
• Patient with an indication to start treatment with Elexacaftor/Tezacaftor/Ivacaftor according to the Marketing Authorization.
• Patient who has not received treatment with CFTR modulators in the 6 months preceding inclusion.
• No opposition expressed by the patient (if ≥ 18 years) or by at least one of the holders of parental authority and the child (if < 18 years).
• Be affiliated to a social security scheme or be a beneficiary of such a scheme.

Exclusion Criteria:

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• Refusal to participate
• Patients and/or holders of parental authority presenting difficulties in understanding and/or communication.
• Inability to complete a reliable food collection.
• Any pathological condition making interpretation of results difficult from the investigator's point of view.
• Transplant patient
• Pregnant or breastfeeding woman
• Person under guardianship or curatorship.