Association between body mass index and irritable bowel syndrome in the young Japanese population: a cross-sectional study.

PURPOSE: The association between body mass index (BMI) and irritable bowel syndrome (IBS) has been inconsistent in the Asian population. Also, no evidence regarding this issue in the young population exists. The aim of the present study is to investigate the association between BMI and IBS based on the Rome III criteria in young Japanese people. METHODS: This study was a cross-sectional study consisted of 8923 Japanese university students. The definition of IBS was based on the Rome III criteria. BMI was divided into four categories (quartiles) on the basis of the study subjects' distribution (lowest, low, moderate, and high [reference]). The definition of lean, normal, and overweight was BMI < 18.5 kg/m2, 18.5 ≤ BMI < 25 kg/m2 (reference), and 25 ≤ BMI kg/m2, respectively. Age, sex, drinking, smoking, exercise habit, anemia, and sports injury were selected a priori as potential confounding factors. RESULTS: The prevalence of IBS was 6.5%, with females having a significantly higher prevalence than males (6.0% vs. 7.2%, p = 0.029). In females, being overweight was independently positively associated with IBS after adjustment (adjusted odds ratio [OR]: 1.81 [95% confidence interval (CI): 1.13-2.79]). In contrast, in males, no association between being lean or overweight and IBS was found. CONCLUSIONS: Among the young Japanese population, being overweight might be independently positively associated with prevalence of IBS in females but not in males.