Efficacy of heat-treated postbiotic Lacticaseibacillus rhamnosus in patients with functional bowel disorders: a randomized, double-blind, placebo-controlled clinical trial

Functional bowel disorders (FBDs) are characterized by chronic abdominal discomfort, altered bowel habits, and bloating, impairing quality of life. Current treatments, including dietary interventions and laxatives, have limited effectiveness and raise safety concerns. Although probiotic-based interventions have gained attention, their mechanisms remain poorly understood. This randomized, double-blind, placebo-controlled pilot trial tested the heat-treated postbiotic Lacticaseibacillus rhamnosus IDCC 3201 (RHT) over an 8-week period in patients with FBDs (RHT, n = 19; placebo, n = 15). Outcomes were measured using the IBS Symptom Severity Scale (IBS-SSS) and IBS Quality of Life (IBS-QOL) questionnaire. Results suggested that the RHT group showed reductions in IBS-SSS scores, alongside improvements in IBS-QOL and bowel activity across physical and psychosocial domains. Gut microbiota profiling revealed decreased Klebsiella pneumoniae and increased beneficial taxa, including Fusicatenibacter saccharivorans and Bacteroides caccae. Metabolomics analysis revealed progressive alterations in the RHT group, with clear distinction from baseline by week 8. Amino acid metabolism-related metabolites increased, whereas inflammation-associated eicosanoids decreased. These findings suggest that RHT alleviates FBD symptoms and improves quality of life by modulating gut microbiota and fecal metabolome, supporting its potential as a postbiotic-based therapeutic strategy.