Impact of gluten intake on clinical outcomes in patients with chronic inflammatory diseases initiating biologics: Secondary analysis of the prospective multicentre <scp>BELIEVE</scp> cohort study

Chronic inflammatory diseases (CIDs) pose a growing healthcare challenge, with a substantial proportion of patients showing inadequate response to biological treatment. There is renewed interest in dietary changes to optimize treatment regimens, with a growing body of evidence suggesting beneficial effects with adherence to a gluten-free diet. This study compared the likelihood of achieving clinical response to biological treatment after 14-16 weeks in patients with CID with high versus low-to-medium gluten intake. Secondary outcomes of interest included changes in disease activity, health-related quality of life and C-reactive protein. The study was a multicentre prospective cohort of 193 participants with a CID diagnosis (i.e. Crohn's Disease, Ulcerative Colitis, Rheumatoid Arthritis, Axial Spondyloarthritis, Psoriatic Arthritis or Psoriasis) who initiated biological treatment between 2017 and 2020. Participants were stratified based on their habitual gluten intake: the upper 33.3% (high gluten intake) and the remaining 66.6% (low-to-medium gluten intake). The proportion of patients achieving clinical response to biological treatment after 14-16 weeks was compared using logistic regression models. The median gluten intake differed significantly between groups (12.5 g/day vs. 5.9 g/day, standardized mean difference = 1.399). In total, 108 (56%) achieved clinical response to treatment, with no difference between 35 (55%) in the high gluten group and 73 (57%) in the medium-to-low gluten group (OR = 0.96 [0.51-1.79], p = 0.897). No differences were found with secondary outcomes. In conclusion, this study found no association between gluten intake and response to biological treatment in patients with CID.