Background and objectives: Although the association between dietary protein intake and inflammatory bowel disease (IBD) risk has been investigated, the results are inconsistent. Therefore, we conducted a meta-analysis to reassess the relationship between dietary protein intake and IBD risk.

Methods and study design: The PubMed, Web of Knowledge, and Wanfang databases were searched for pertinent studies through January 31, 2020. Relative risks (RRs) with 95% confidence intervals (CIs) were derived using a random-effect model. Subgroup analyses according to disease type, geographic location, and sex; sensitivity analysis; and publication bias analysis were performed.

Results: The current report includes 8 articles consisting of 12 studies with 1069 cases and 330,676 participants. The pooled RR (95% CI) of the highest vs. the lowest categories of dietary protein intake for the IBD risk was 1.561 (0.384-6.347) in cohort studies and 1.060 (0.663-1.694) in case-control studies. Evidence of heterogeneity was found both in cohort studies (I2=86.4%, p=0.007) and in case-control studies (I2=49.0%, p=0.039). However, the association was significant among Asian populations (RR=1.675, 95% CI=1.096-2.559) but not in other populations. We did not find any relationship of dietary protein intake with the risk of either Crohn's disease or ulcerative colitis.

Conclusions: Based on limited information, the highest dietary protein intakes among Asians may increase the risk of IBD, undifferentiated for ulcerative colitis or Crohn's disease. This may reflect dietary patterns for which protein is a marker rather than implicate protein itself.