Search strategy
The present meta-analysis was performed according to the Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines23 and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We conducted a systematic literature search in PubMed, Web of Science, Embase, Cochrane Library and Chinese National Knowledge Infrastructure (CNKI) databases. The last search was conducted on April 30, 2020. We searched with a combination of keywords, including “adipokines” or “resistin” or “RETN” combined with “Crohn’s disease” or “CD” or “ulcerative colitis” or “UC” or “inflammatory bowel disease” or “IBD”. The corresponding Chinese terms were applied for CNKI. We also checked other relevant publications on the references of the retrieved studies.