Table 2. Summary of included studies establishing the effect of probiotics in IBS patients.

GI, gastrointestinal; IBS, irritable bowel syndrome; IBS-C, IBS with predominant constipation; IBS-D, IBS with predominant diarrhea

Author	Study design	Study population	Salient remarks
Nobaek et al., 2000 [56]	Randomized control trial	60 IBS patients with a regular colonoscopy/barium enema	Flatulence reduced significantly in the test group. Abdominal pain reduced in both groups. Better overall GI function was observed during the follow-up.
Saggioro, 2004 [63]	Clinical trial	70 IBS patients (31 males and 39 females) with a mean age of 40 years, including patients ranging between 26 and 64 years of age	Efficacious in reducing the severity of abdominal pain after a short course of probiotic therapy, responses that were checked on days 14 and 28 proved beneficial in IBS patients.
Kim et al., 2005 [57]	Randomized control, double-blind	IBS patients	Reduction in flatulence and colonic transit time without altering bowel function.
Kim et al., 2006 [65]	Double-blind, prospective study	40 IBS patients	Marked reduction in the frequency and severity of abdominal pain in the subjects (P=0.044, P=0.038) but not in the placebo group.
Dolin et al., 2009 [58]	Randomized, double-blind	52 IBS-D patients	Significantly reduced the average number of bowel movements (P=0.042).
Guglielmetti et al., 2011 [59]	Randomized control trial	122 IBS patients	Improvement in pain, distention, urgency, and digestive disorder (P<0.0001).
Kruis et al., 2012 [64]	Double-blind, prospective study	120 IBS patients	Significant improvement noted to be Δ20.0% points (95% CI 2.6, 37.4), P=0.01, and Δ18.3% points (95% CI 1.0, 35.7), P=0.02, after 10 and 11 weeks, respectively. Best responses were from those with prior alteration in enteric microflora (Δ45.7% points, P=0.029) and also showed greatest change in all groups.
Yoon et al., 2014 [62]	Randomized, double-blind trial	49 IBS patients (probiotics: 25, placebo: 24)	Symptoms such as abdominal pain/discomfort, bloating, stool frequency, and consistency were relieved in the probiotics group compared to placebo (68% vs. 37.5%; P<0.05).
Mezzasalma et al. 2016, [60]	Randomized, double-blind, three-arm parallel-group trial	150 IBS-C patients	Patients responded well to each symptom. Effectiveness proved well.
Sun et al., 2018 [61]	Randomized, double-blind, prospective study	200 IBS-D patients	Overall symptoms, stool frequency, and quality of life improved.