A total of 140 subjects who fulfilled Rome IV criteria for IBS will be recruited from a tertiary medical centre and among public volunteers. The depression status and categories will be assessed using the Centre Epidemiologic Studies Depression Scale Revised questionnaire (CESD-R): normal mood (score<16), or subthreshold depression (score>16). The subjects are randomised and blinded into four groups: Group A (Normal mood with placebo, n=35), Group B (Normal mood with probiotics, n=35), Group C (Subthreshold depression with placebo, n=35) and Group D (Subthreshold depression with probiotics, n=35). The subjects will be instructed to consume two bottles of cultured milk drink daily for 12 weeks. The probiotic cultured milk drinks contained 10^9 cfu L. CASEI-01 and LA-5. The severity of depression will be measured using Patient Health Questionnaire (PHQ-9) at pre- and post-12-week intervention. Secondary outcome on IBS symptoms severity will be assessed with IBS Symptoms Severity Score (IBS-SSS) and IBS Quality of Life (IBS-QOL).
Irritable bowel syndrome (IBS) is frequently associated with any form of psychiatric comorbidities including subthreshold or subclinical depression. Modification of gut ecology with probiotics has implicitly improved IBS and depressive symptoms. However, the efficacy of probiotics on IBS with existing subthreshold depression remain elusive. Therefore, the aim of this study is to evaluate the effects of lactobacillus-containing cultured milk drink on depression scores in adults diagnosed with IBS.