Subclinical intestinal inflammation and gut dysbiosis have been reported in patients with spondyloarthritis (SpA). In common practice, rheumatologists are increasingly confronted with patients with inflammatory rheumatism who are on gluten-free diets (GFDs), despite the lack of reliable data from controlled studies. This study aims to determine the impact of a GFD on the quality of life of patients with axial SpA.

The GlutenSpA study is a 24-week, randomized, double-blinded, placebo-controlled, multicenter trial. Patients with axial SpA (n=200) will follow a 16-week GFD and be randomly assigned (1:1) to an experimental or control arm. In the experimental arm with receive at least 6 gluten-free breads per day + 200 g of gluten-free penne pasta per week + 6 rice flavor capsules per day. The control arm will receive at least 6 gluten-containing breads per day + 200 g of gluten-containing penne pasta per week + 6 vital gluten-containing capsules per day.

At baseline, the dietician will explain to the patients how to properly follow a GFD during a face-to-face interview. The patient's compliance to the GFD will be evaluated by the dietician at S2, S16, an S24 using an online 3-day alimentary questionnaire.

The bread and penne pasta were chosen for their visual resemblance and similar taste to maximize the blindness of the study. In order to reach the daily amount of gluten in a standard diet (estimated in France between 10 and 15 g/d) in the control arm, each day patients will have to ingest six capsules of vital gluten wheat made for the study. Vital gluten flour is an over-the-counter food supplement used to enrich a protein diet or as a base for making products, such as seitan. Capsules will be made using commercially available vital gluten and contain 0.35 g of gluten per capsule. The total amount of gluten in the control arm will be approximately 10.5 g/day.

After the 16-week GFD, patients will be offered to follow or not follow the GFD according to their own decision for an 8-week open-labelled follow-up period. The study duration for each patient is 24 weeks. The patient recruitment is expected to last 2 years

Inclusion Criteria:

• diagnosis of axial SpA defined by ASAS criteria
• Rheumatologist not wish to change the treatment within 4 months of inclusion,
• stable treatment (NSAID and/or DMARD) for at least 3 months but no corticosteroid infiltration in the month prior to inclusion,
• able to follow a GFD and to provide written informed consent and submit to the requirements of the study

Exclusion Criteria:

• Any diet at the time of inclusion or within 3 months prior to inclusion;
• have a history of celiac disease;
• received antibiotic treatment within 3 months of inclusion or are taking a probiotic;
• are pregnant, breastfeeding,
• not covered by social security;
• minors or adults under the protection of the law or under the protection of justice.