The JIA-ED study is a pilot project. Based on experience in another inflammatory disease, a 4-week period was extrapolated as sufficient to assess the effectiveness of the experimental intervention. This observation is supported by literature data showing that, halfway through phase I of the CDED (Crohn Diseasse Exclusion Diet), it is already possible to identify a subset of patients with Crohn's disease who are responsive to the dietary treatment and who also have a higher likelihood of achieving clinical remission by the end of the first phase of the diet itself.

Inclusion Criteria:

• Confirmed diagnosis of juvenile idiopathic arthritis (JIA) in the forms of enthesitis-related arthritis and oligoarticular forms according to the ILAR 2001 criteria (https://medicalcriteria.com/web/reujia/);
• Age between 6 and 18 years (not yet 18);
• Active disease of mild to moderate severity, assessed through the Juvenile - Arthritis Disease Activity Score (JADAS10) tool (Trincianti C. et al., American College Rheumatology, 2021);
• For study groups 2 and 3: failure of ongoing pharmacological therapy at the time of screening, defined as a failure to achieve at least a 20% reduction in JADAS10 values after 3 months of initiating DMARD therapy or biologic medication, or if the disease is inactive on such therapy, a 20% increase in those values;
• Signed informed consent.

Exclusion Criteria:

• Patients requiring systemic immunosuppressive therapy for active uveitis;
• Patients undergoing therapy with systemic corticosteroids (defined as prednisone equivalent >0.5 mg/kg for >7 days) or intra-articular corticosteroids in the 3 months prior to enrollment;
• Patients with fecal calprotectin values > 250 mcg/g at the time of screening;
• Use of antibiotics in the month prior to enrollment.