Dietary risk factors for inflammatory bowel disease: A systematic review and meta-analysis

Background: Existing evidence indicates that diet is a modifiable risk factor for IBD. However, data on certain nutrients, food groups and individual food items and their associations with IBD is still lacking. This review aims to systematically assess which dietary factors are associated with the onset of IBD. Method: Computerised bibliographic searches of Ovid MEDLINE, Web of Science, and the Cochrane Library (Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Methodology Register) were conducted. Studies were included if they were case-control, cohort studies or randomised controlled trials (RCTs) investigating the association between dietary risk factors and onset of IBD and if they included patients with a diagnosis of IBD (including Crohn's Disease [CD] and/or Ulcerative Colitis [UC]), defined and measured according to clinical symptoms, endoscopy, and histology. Summary relative risks (RRs) were calculated using random effects models to provide risk estimates for the associations between dietary factors and IBD. Results: Twenty eligible studies were identified and included in the systematic review and meta-analysis, encompassing 10 case-control and 10 cohort studies, with no RCTs identified. A total of 4,332 patients with IBD were included (1554 CD; 2550 UC; 225 IBD; 3 IBD unclassified [IBDU]). Nine significant predictors of IBD risk were identified. Pooled analysis highlighted a decreased risk of overall IBD was associated with high intakes of fruit (RR 0.70, 95% CI 0.45–0.96), vegetables (RR 0.48, 95% CI 0.19–0.78), carbohydrates (RR 0.70, 95% CI 0.51–0.89), rice (RR 0.65, 95% CI 0.32–0.97), milk (RR 0.43, 95% CI 0.25–0.62), dairy (RR 0.67, 95% CI 0.38–0.97), vitamin C (RR 0.65, 95% CI 0.35–0.96) and vitamin D (RR 0.72, 95% CI 0.46–0.97). High protein intake was associated with a 4.1-fold (RR 4.07, 95% CI 1.51–6.62) increased risk of IBD. Conclusion: This systematic review and meta-analysis highlights the potential role of diet as a modifiable risk factor for IBD. From a patient management perspective, our results may aid clinicians and dietary practitioners in guiding dietary interventions and modifications, particularly in those at a high-risk of developing the disease. Moreover, our results provide novel data on specific food items and vitamins which may confer a protective effect against IBD, of which evidence has previously been lacking.