Efficacy of probiotics, prebiotics and synbiotics in irritable bowel syndrome: a systematic review and meta- analysis of randomized, double-blind, placebo-controlled trials

Introduction. Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that affects the quality of life of numerous people worldwide.Gap statement. The therapeutic role of gut microbiota modulation in IBS remains controversial.Aim. We aimed to assess the efficacy of probiotics, prebiotics or synbiotics in patients with IBS.Methodology. We searched MEDLINE and EMBASE up to 1 August 2023, to identify the randomized, double-blind, placebo -controlled trials investigating the effectiveness of probiotics, prebiotics or synbiotics among patients with IBS. Pooled analyses of the effects of probiotics in relieving IBS symptoms were calculated using a random-effects model. Further subgroup analyses were performed by different genera, doses and duration of treatment.Results. Our final analysis included 52 trials involving 6289 IBS patients. Probiotics significantly increased the overall response rate (RR:1.64; P<0.00001), subjective relief rate (RR:1.50; P=0.0002) and abdominal pain relief rate (RR:1.69; P<0.00001). As for specific genera, mixed probiotics (RR:1.41; P=0.0001), Bifidobacterium (RR:1.76; P<0.00001), Lacto-bacillus (RR:1.97; P=0.0004) and Saccharomyces (RR:1.31; P=0.0004) markedly relieved IBS symptoms. Mixed probiotics (RR:1.31; P=0.005), Lactobacillus (RR:2.22; P=0.04) and Bifidobacterium (RR:1.62; P<0.0001) elevated patients' subjective relief rate. Besides, probiotics effectively relieved the abdominal pain in IBS patients (RR:1.69; P<0.00001). Probiotics appeared to show a remarkable beneficial role at a dose of 109 c.f.u./day or above (RR:1.662; P<0.0001) and started to work at 4 weeks (RR 1.72; P<0.00001). Efficacy of prebiotics and synbiotics in IBS remained uncertain, due to the deficiency of available RCTs.Conclusions. Probiotics have a therapeutic role in IBS. However, the effect of different probiotics varies. The minimal effective dose of probiotics may be 109 c.f.u./day. With appropriate probiotic formula, the therapeutic effect can occur at 4 weeks. These data provide a basis for further research on the optimal probiotic therapy in IBS.