Systematic review and meta-analysis: the association of a pre-illness Western dietary pattern with the risk of developing inflammatory bowel disease.

Objective Previous studies have presented conflicting results on Western diets and the risk of inflammatory bowel disease (IBD). This study aimed to evaluate the role of a pre-illness Western dietary pattern in the development of IBD. Methods The Western dietary pattern was defined as that met at least two of the following, either a high intake of refined grains, red and processed meat, animal protein, animal fats or high-fat dairy products, or with a low consumption of fruit and vegetables. Four medical databases (PubMed, EMBASE, the Cochrane Library and the China National Knowledge Infrastructure) were searched to identify all relevant references. Risk estimate and corresponding 95% confidence interval (CI) were pooled using a random-effects model. Results Nine studies (seven case-control studies and two prospective cohorts) were included, with a total of 1491 IBD cases and 53 089 controls. A Western dietary pattern was associated with a risk of all IBD (relative risk [RR] 1.92, 95% CI 1.37-2.68) and separately with Crohn's disease (CD) (RR 1.72, 95% CI 1.01-2.93) and ulcerative colitis (UC) (RR 2.15, 95% CI 1.38-3.34). Subgroup analysis by region showed that a Western dietary pattern was associated with the risk of CD and UC for studies performed in Europe (RR 2.25, 95% CI 1.44-3.50 for CD; RR 2.65, 95% CI 1.61-4.36 for UC). The pooled RR was 2.26 (95% CI 1.42-3.59) in the pediatric CD subgroup. Conclusion This meta-analysis indicates that a pre-illness Western dietary pattern may increase the risk of developing CD and UC.