Inflammatory bowel diseases (IBD) can be broadly divided into Crohn's disease (CD) and ulcerative colitis (UC) from their clinical phenotypes. Over 150 host susceptibility genes have been described, although most overlap between CD, UC and their subtypes, and they do not adequately account for the overall incidence or the highly variable severity of disease. Replicating key findings between two long-term IBD cohorts we have defined distinct networks of taxa associations within intestinal biopsies of CD and UC patients. Disturbances in an association network containing taxa of the Lachnospiraceae and Ruminococcaceae families, typically producing short chain fatty acids, characterize frequently relapsing disease and poor responses to treatment with anti-TNF-α therapeutic antibodies. Alterations of taxa within this network also characterize risk of later disease recurrence of patients in remission after the active inflamed segment of CD has been surgically removed.

Background Many inflammatory bowel disease (IBD) patients follow a restrictive diet due to perceived positive effects on their symptoms. We assessed the prevalence of vegetarian (VD) and gluten-free diets (GFDs) in IBD patients, the reasons for following such a diet, and whether nutrition has an impact on disease activity and microbiota composition. Methods We included 1254 patients from the Swiss Inflammatory Bowel Disease Cohort Study with prospective acquisition of clinical data and psychosocial, disease-related and lifestyle factors between 2006 and 2015. Dietary habits were assessed through a self-report questionnaire. In 92 patients, we analysed intestinal mucosa-associated microbial composition using high-throughput sequencing. Results Overall, 4.1% ( n = 52) of the patients reported following a VD and 4.7% ( n = 54) a GFD. No differences regarding disease activity, fistula, hospitalization or surgery rates were observed. Patients on a VD or GFD had significantly higher levels of post-traumatic stress symptoms. Furthermore, GFD patients had significantly higher anxiety and depression symptom levels. The gut microbiota composition in IBD patients following a VD or GFD was significantly different compared to that of omnivores. Conclusions Although we did not identify a relevant impact of a specific diet on the course of the disease, there was a significant association with lower psychological well-being in VD and GFD patients.

Highlights d Inflammatory cues and the microbiota modulate Gpr35 expression across species d LPA modulates GPR35-dependent functions in zebrafish and mouse macrophages d GPR35-expressing macrophages have a protective role during intestinal inflammation d GPR35 controls intestinal inflammation by inducing TNF and corticosterone