Impact of Body Mass Index on the Development of Inflammatory Bowel Disease: A Systematic Review and Dose-Response Analysis of 15.6 Million Participants

Abstract

Background: A growing trove of literature describes the effect of malnutrition and underweight on the incidence of inflammatory bowel disease (IBD). However, evidence regarding the association between underweight or obesity and IBD is limited. The study aimed to assess the association of body mass index (BMI) with a risk of IBD (Crohn’s disease (CD) and ulcerative colitis (U.C.)) incidence. Methods: We systematically searched PubMed/Medline, Cochrane, Web of Science, and Scopus for observational studies assessing the association between BMI and IBD that were published up to 30 June 2020. We estimated pooled hazard ratios (HR) with corresponding 95% confidence intervals (CI). Random effect dose-response meta-analysis was performed using the variance weighted least-squares regression (VWLS) models to identify non-linear associations. Results: A total of ten studies involving 15.6 million individuals and 23,371 cases of IBD were included. Overall, obesity was associated with an increased IBD risk (HR: 1.20, 95% CI: 1.08–1.34, I2 = 0%). Compared to normal weight, underweight (BMI < 18.5 kg/m2) and obesity (BMI ≥ 30 kg/m2) were associated with a higher risk of CD, and there was no difference in the risk of U.C. among those with BMI < 18.5 kg/m2 and BMI ≥ 30 kg/m2. There was a significant non-linear association between being underweight and obesity and the risk of development of CD (Coef1 = −0.0902, p1 < 0.001 Coef2 = 0.0713, p2 < 0.001). Conclusions: Obesity increases the risk of IBD development. Underweight and obesity are independently associated with an increased risk of CD, yet there is no evident association between BMI and the risk of U.C. Further studies are needed to clarify the underlying mechanism for these findings, particularly in CD.

Lifestyle factors associated with inflammatory bowel disease: data from the Swiss IBD cohort study

“…A recently published meta-analysis reported an positive association between underweight and the onset of CD, but not for UC [40].…”

Smoking and drinking habits relating to development of ulcerative colitis in Japanese: A multicenter case–control study

“…24 In a recent systematic review, both underweight and obese status were independently associated with Crohn's disease, but BMI was not significantly associated with UC. 25 The present study has three main strengths. First, the possibility of reverse causality was minimized by including only patients with newly diagnosed UC.…”

Lifestyle Factors and Silent Inflammatory Bowel Disease

“…Each of these variables been studied in the context of IBD and have exhibited at least potential to influence disease activity and other patient-related outcomes [5,6]. For example, healthy dietary patterns (e.g., consumption of foods like fruits and vegetables even when asymptomatic and/or avoiding diets rich in processed proteins and/or carbohydrates) and having a normal body mass index (BMI) (e.g., 18.5-24.9 kg/m 2 ) appear to have positive effects on treatment efficacy, the course of IBD, and/ or likelihood of experiencing IBD-associated symptoms [7][8][9][10]. Regular exercise has also previously been associated with several positive outcomes, including reduction of IBDrelated disease activity and improvement in the severity or frequency of some symptoms (e.g., fatigue), particularly in the setting of quiescent disease [11,12].…”