METHODS: A cross-sectional study of consecutive Asian adults attending a primary healthcare setting was conducted. This study was conducted in 2 phases: The association between BMI and common FGIDs (functional diarrhea/FD, irritable bowel syndrome/IBS, functional diarrhea and functional constipation/FC) was studied initially. The influence of anxiety and depression on BMI and FGIDs was additionally explored in phase 2.

RESULTS: A total of 1002 subjects (median age 32 years, 65.4% females, 90.7% Malay ethnicity, 73.2% higher than secondary level education) were recruited between August 2019 to January 2020. The majority of subjects were obese (39.2%), and had central obesity (51.7%), while 6.1% had metabolic syndrome. The prevalence of FD, IBS, functional diarrhea and FC were 7.5% (n = 75), 4.0% (n = 40), 1.2% (n = 12) and 10.5% (n = 105) respectively, based on the Rome III criteria. Among individual FGIDs, FD subjects had more underweight adults (BMI<18.5kg/m2) compared to controls (13.3% vs 3.5%, P = 0.002) and being underweight remained as an independent association with FD [OR = 3.648 (95%CI 1.494-8.905), P = 0.004] at multi-variate analysis. There were no independent associations between BMI and other FGIDs. When psychological morbidity was additionally explored, anxiety (OR 2.032; 95%CI = 1.034-3.991, p = 0.040), but not depression, and a BMI<18.5kg/m2 (OR 3.231; 95%CI = 1.066-9.796, p = 0.038) were found to be independently associated with FD.