Table 1.

Studies on the impact of probiotics on IBS patients.

Paper	Research Type	Participants Selection Criteria	Participants 1	IBS Subtype	Preparation (Dosage)	Placebo/Control (Dosage)	Duration	Outcomes
Sen et al. (2002) [79]	The randomized, double-blind, placebo-controlled study	Rome I	12 males/females 18–65 y 2	wd 3	ProViva (oatmeal gruel, 5 × 107 cfu/mL 4 of Lb. plantarum 299V) 125 mL/d 5	Oatmeal gruel 125 mL/d	First 4 weeks of placebo administration, then 4 weeks of treatment	No beneficial effect
Whorwell et al. (2006) [89]	The randomized, double-blind, placebo-controlled, multicenter, dose-ranging stud	Rome II	362 females 18–65 y	All	Excipient (no data on used compounds), B. infantis 35,624 (three different doses: 1.0 × 106, 1.0 × 108, or 1.0 × 1010 cells/capsules) 1 capsule/d 6	Excipient (no data on used compounds) 1 capsule/d	2 weeks of the run-in period, then 4 weeks of treatment, and 2 weeks of follow up	Improvement of IBS symptoms The effective dose was 1.0 × 108 cells/capsule
Barrett et al. (2008) [113]	Uncontrolled pilot study	Rome II	18 males/females 20–70 y	All	Yakult® (sucrose, skim milk powder, dextrose, 6.5 × 109 cells/dose L. casei Shirota) 65 mL/d	na 7	Up to 2-week run-in period, 6 weeks of treatment	Reduction in SIBO 8 Regression of ERBHAL 9, accompanied by improved abdominal symptoms
Sinn et al. (2008) [115]	The randomized, double-blind, placebo-controlled human study	Rome III	40 males/females 18–70 y	All	Excipient (no data on used compounds), freeze-dried Lb. acidophilus SDC 2012, and Lb. acidophilus SDC 2013 (a total of 2.0 × 109 cfu/mL) 2 capsules/d	Excipient (no data on used compounds) 2 capsules/d	4 weeks	Improved IBS symptoms
Hong et al. (2009) [116]	The randomized, double-blinded, placebo-controlled parallel-group clinical study	Rome III	70 males/females 19–75 y	All	B. bifidum BGN4, B. lactis AD011, Lb. acidophilus AD031, Lb. casei IBS041 (a total of 2.0 × 1010 cfu/packet 10 viable, lyophilized probiotics) 2 packets/d 11	Skim milk powder 2 packets/d	8 weeks	Reduced abdominal pain and defecation discomfort
Ligaarden et al. (2010) [88]	The randomized double-blind, placebo-controlled, crossover trial	Rome II	16 males/females 18–75 y	All	1010 cfu/capsule 12 Lb. plantarum MF1298 (live, freeze-dried) 1 capsule/d	No data on used compounds 1 capsule/d	1 week run-in period, followed by 3 weeks of treatment (probiotc/placebo), then 4 weeks of wash-out phase, and another 3 weeks of alternate treatment (placebo/probiotic)	Adverse effects of probiotic
Pedersen et al. (2010) [81]	Placebo-controlled study	Rome II	61 males/females 18–79 y	All	Milk (a total of 107–109 cfu/g 13 acidifiers: Lb. delbruckeii ssps. bulgaricus, S. thermophilus; probiotics: 5 × 107 cfu/mL Lb. paracasei F19, 5 × 107 cfu/mL Lb acidophilus LA-5, 5 × 107 cfu/mL B. lactis BB-12) 400 mL/d	Milk (acidifiers: D-(+)-gluconic acid, δ-lactone) 400 mL/d	2 weeks of wash-out period, then 8 weeks of treatment	Observed effects of treatment were due to acidified milk itself, not the probiotic
Simrén et al. (2010) [82]	The randomized, double-blind, placebo-controlled study	Rome II	74 males/females 18–70 y	All	Cultura (fermented with: Lb. bulgaricus, S. thermophilus; containing probiotics: 5.0 × 107 cfu/mL Lb. paracasei F19, 5.0 × 107 cfu/mL Lb. acidophilus La5, 5.0 × 107 cfu/mL B. lactis Bb12) 400 mL/d	Acidified milk 400 mL/d	2 weeks of the run-in period, then 8 weeks of treatment, and 8 weeks of follow-up	No beneficial effect
Guglielmetti et al. (2011) [90]	The prospective, multicenter, randomized, double-blind, placebo-controlled, two-arm nutritional study	Rome III	122 males/females 18–68 y	wd	Excipient (no data on used compounds), 1 × 109 cfu/capsule B. bifidum MIMBb75 1 capsule/d	Excipient (no data on used compounds), maltodextrin 1 capsule/d	2 weeks of the run-in period, then 4 weeks of treatment, and 2 weeks of wash-out phase	Improvement of IBS symptoms Maintained beneficial impact of probiotic during the wash-out period
Michail and Kenche (2011) [117]	The randomized, double-blind, placebo-controlled trial	Rome III	24 males/females average age of 21.8 ± 17	IBS-D	VSL#3 (cornstarch, S. thermophilus, B. breve, B. longum, B. infantis, Lb acidophilus, Lb plantarum, Lb paracasei, Lb. bulgaricus) 9.0 × 1011 cells/d 14	Cornstarch	8 weeks	No impact on fecal microbiota No influence on BMI
Søndergaard et al. (2011) [83]	The randomized, double-blind, placebo-controlled, parallel-group trial	Rome II	64 males/females 18–70 y	wd	Cultura 1000 mL/d	Acidified milk 1000 mL/d	2-week run-in period, then 8 weeks of treatment	No effect on IBS symptoms
Cui and Hu (2012) [118]	The double-blind, placebo-controlled study	Rome III	60 males/females average age between 44.38 ± 15.08 and 48.45 ± 14.08	All	Bifid triple viable capsule (B. longum, Lb. acidophilus) 6 capsules/d	No data on used compounds 600 mg/d 15	4 weeks	Improvement in overall IBS symptoms Higher abundance of gene copies of Bifidobacterium spp. and Lactobacillus spp. in feces
Dapoigny et al. (2012) [100]	The prospective, multicenter, randomized, double-blind, placebo-controlled, parallel-group pilot trial	Rome III	50 males/females 18–70 y	All	2 × 108 cfu/capsule Lb. rhamnosus (total freeze-dried culture) 3 capsules/d	No data on used compounds 3 capsules/d	2 weeks of the run-in period, then 4 weeks of treatment, and 2-week follow-up	Improvement of symptoms only among IBS-D patients
Ducrotté et al. (2012) [80]	The multicenter, parallel-group, double-blind, placebo-controlled study	Rome III	216 males/females 18–70 y	All	Excipients (potato starch, magnesium stearate) and 1 × 1010 cfu/capsule Lb. plantarum 299V DSM 9843	Potato starch and magnesium stearate	4 weeks of treatment, then 3 weeks of follow-up	Potentially beneficial in the management of IBS
Kruis et al. (2012) [107]	The randomized, double-blind, parallel-group, monocenter study	Rome II	120 males/females 18–65	IBS-C, IBS-D	MUTAFLOR® (2.5–25 × 109 cfu/capsule Escherichia coli Nissle 1917) 1 capsule/d (first 4 days) 2 capsules/d (the rest of the trial)	No data on used compounds 1 capsule/d (first 4 days) 2 capsules/d (the rest of the trial)	12 weeks	Therapeutic potential for PI-IBS 16 PA-IBS 17 subjects
Murakami et al. (2012) [91]	The placebo-controlled, double-blind, crossover trial	Rome III	35 males/females ≥ 6 y	wd	Corn starch, maltitol syrup, hydroxypropyl methylcellulose, calcium stearate, ≥1.0 × 1010 cfu/capsule Lb. brevis KB290 1 capsule/d	Corn starch, maltitol syrup, hydroxypropyl methylcellulose, calcium stearate1 capsule/d	4-week run-in period, followed by 4 weeks of treatment (probiotic/placebo), then 4 weeks of wash-out phase, and another 4 weeks of alternate treatment (placebo/probiotic)	Increased abundance of Bifidobacterium spp. and decrease of Clostridium spp. in fecal samples Improvement of IBS symptoms and subjects’ quality of life
Amirimani et al. (2013) [84]	The randomized parallel-group, single-blind, placebo-controlled study	Rome III	72 subjects (no information on sex, and age)	wd	Biogaia® (1 × 108 viable cells of Lb. reuteri) 1 tablet/d 18	1 tablet/d	4 weeks	Increased frequency of defecation No vital differences in IBS symptoms
Roberts et al. (2013) [85]	The randomized, double-blind, placebo-controlled trial	Rome III	179 males/females 18–65 y	wd	Yogurt with 1.2 × 109 cfu/cup 19 of standard strains (S. thermophilus CNCM I-1630, Lb. bulgaricus CNCM I-1632, and I-1519) with the addition of 1.25 × 1010 cfu/cap B. lactis DN-173 010 2 cups/d 20	Milk-based non-fermented dairy product without probiotics and with similar lactose content to the test product2 cups/d	12 weeks	No impact of tested probiotic on IBS symptoms severity
Abbas et al. (2014) [110]	The randomized, double-blind, placebo-controlled trial	Rome III	72 males/females 18–60 y	IBS-D	S. boulardii 750 mg/d	No data on used compounds 750 mg/d	2 weeks run-in period, then 6 weeks of treatment	Decreased blood levels of pro-inflammatory cytokines (IL 21-8, TNF-α 22) Increased tissue levels of anti-inflammatory cytokines (IL-10)
Lorenzo-Zúñiga et al. (2014) [86]	The multicenter, randomized, double-blind, placebo-controlled intervention clinical trial	Rome III	84 males/females 20–70 y	IBS-D	Lb. plantarum CECT7484, Lb. plantarum CECT7485, and P. acidilactici CECT7483 (ratio 1:1:1; a total of 1–3 × 1010 cfu/capsule in high dose or 3–6 × 109 cfu/capsule in low dose) 1 capsule/d	No data on used compounds 1 capsule/d	6 weeks	Improvement of IBS-related life quality No significant relief in the severity of IBS symptoms Lack of significant improvement of IBS symptoms Amelioration of quality of subjects’ life
Sisson et al. (2014) [119]	The single-center, randomized, double-blind, placebo-controlled trial	Rome III	186 males/females 18–65 y	All	Symprove (water-based barley extract, Lb. rhamnosus NCIMB 30174, Lb. plantarum NCIMB 30173, Lb. acidophilus NCIMB 30175, E. faecium NCIMB 30176; total of 1.0 × 1010 bacteria/50 µ) 1 mL/kg a day 23	Water, flavorings 1 mL/kg a day	12 weeks of treatment, and 4 weeks of follow-up	Significantly improved symptoms of IBS, especially pain and bowel habits Ameliorated symptoms severity The effect was not sustained during the follow-up period
Urgesi et al. (2014) [101]	The monocentric, double-blind, placebo-controlled, parallel-group clinical trial	Rome III	52 males/females 18–75 y	wd	Colinox® (excipient—no data on used compounds, simethicone, 1.5 × 109 spores/g 24 B. coagulans) 3 tablets/d	Excipient (no data on used compounds) 3 tablets/d	4 weeks	Significant improvement of IBS symptom
de Chambrun et al. (2015) [108]	The randomized, single-center, double-blind, placebo-controlled, parallel-group clinical study	Rome III	179 males/females 18–75 y	All	8 × 109 cfu/g S. cerevisiae CNCM I-3856 1 capsule/d	Dibasic calcium phosphate 1 capsule/d	2 weeks of the run-in period, then 8 weeks of treatment, and 3 weeks of follow-up	Reduced severity of abdominal pain/discomfort The relief of symptoms was limited to the duration of treatment
Yoon et al. (2015) [120]	The randomized, double-blind, placebo-controlled trial	Rome III	81 males/females 19–75 y	All	LacClean Gold-S® (maltodextrin, corn starch, silicon dioxide, B. bifidum KCTC 12199BP, B. lactis KCTC11904BP, B. longum KCTC 12200BP, Lb. acidophilus KCTC 11906BP, Lb. rhamnosus KCTC 12202BP, S. thermophilus KCTC 11870BP; a total of 5 × 109 viable cells/capsule) 2 capsules/d	Maltodextrin, corn starch, silicon dioxide 2 capsules/d	4 weeks	Increased abundance of administrated probiotic strains in fecal samples Amelioration of diarrhea-predominant symptoms of IBS
Majeed et al. (2016) [102]	The randomized, double-blind, parallel-group, placebo-controlled, multi-centered study	Rome III	36 males/females 18–55 y	IBS-D	Microcrystalline cellulose, starch, sodium starch glycolate, magnesium stearate, and B. coagulans MTCC 5856 2 × 109 spores/tablet 25 1 tablet/d	Maltodextrin 1 tablet/d	90 days	Attenuation of symptoms (bloating, vomiting, stool frequency, abdominal pain, diarrhea) Improved quality of life
Mezzasalma et al. (2016) [121]	The randomized, double-blind, placebo-controlled study	Rome III	157 males/females 18–65 y	IBS-C	Product 1: 5 × 109 cfu Lb. acidophilus DSM 24936, 5 × 109 cfu Lb. reuteri DSM 25175, inulin, silica, talc; product 2: 5 × 109 cfu Lb. rhamnosus DSM 25568, 5 × 109 cfu Lb. plantarum DSM 24937, 5 × 109 cfu B. lactis DSM 25566, inulin, silica, talc	Inulin, silica, talc	60 days of treatment, then 30 days of follow-up	Increasing abundance of tested strains in fecal samples during treatment Probiotic strains remained in the stool samples during follow-up period, except B. lactis Both products diminish severity of IBS-C symptoms
Spiller et al. (2016) [109]	The multi-center, randomized, double-blind, placebo-controlled trial	Rome III	379 males/females 18–75 y	All	S. cerevisiae I-3856 2 capsules/d	No data on used compounds 2 capsules/d	2-week run-in period, then 12 weeks of treatment	Improved GIT symptoms of IBS-C subjects
Compare et al. (2017) [98]	Ex vivo study	Rome III	20 males/females 18–70 y	PI-IBS/IBS-D	Lb. casei DG and its postbiotic	Healthy controls (10 out of 20)	na	Decreased inflammatory mucosal response in ex vivo model of PI-IBS-D subjects
Cremon et al. (2018) [87]	The multicenter, randomized, double-blind, cross-over, placebo-controlled, pilot trial	Rome III criteria	40 males/females 18–65 y	All	Gelatin capsule containing 2.4 × 1010 viable cells of Lb. paracasei CNCM I-1572 2 capsules/d	No data on used compounds 2 capsules/d	2 weeks of the run-in period, next 4 weeks of treatment (probiotic/placebo), followed by 4 weeks of wash-out phase, and another 4 weeks of alternate treatment (placebo/probiotic), then 4-week follow-up	No significant improvement of IBS symptoms compared to placebo Reduced Ruminococcus spp. Diminished levels of pro-inflammatory cytokines IL-6, and IL-15 Increased levels of butyrate
Hod et al. (2018) [122]	The randomized, double-blind, placebo-controlled, parallel-group clinical trial	Rome III	97 females 18–70	IBS-D	BIO-25 (3.0 × 109 cfu/capsule Lb. rhamnosus LR5; 2.0 × 109 cfu/capsule Lb. casei LC5; 1.0 × 109 cfu/capsule Lb paracasei LPC5; 1.0 × 109 cfu/capsule Lb. plantarum LP3; 5.0 × 109 cfu/capsule Lb. acidophilus LA1; 4.0 × 109 cfu/capsule B. bifidum BF3; 1.0 × 109 cfu/capsule B. longum BG7; 2.0 × 109 cfu/capsule B. breve BR3; 1.0 × 109 cfu/capsule B infantis BT1; 2.0 × 109 cfu/capsule S. thermophilus ST3; 3.0 × 109 cfu/capsule Lb. bulgaricus LG1, 3.0 × 109 cfu/capsule L. lactis SL6) 2 capsules/d	Cellulose2 capsules/d	2 weeks of run-in period, then 8 weeks of treatment	No effect on fecal microbiota diversity Increased abundance of Lactobacillus spp. and Lactococcus spp. in stool samples of subjects whose abdominal pain and bloating were reduced Individuals with decreased abdominal pain and improved stool consistency showed a decrease in Bilophila genus prevalence
Ishaque et al. (2018) [123]	The randomized, double-blind, placebo-controlled, equal allocation ratio, parallel-group, clinical trial	Rome III	360 males/females 18–55 y	IBS-D	Bio-Kult® (B. subtilis PXN 21, B. bifidum PXN 23, B. breve PXN 25, B. infantis PXN 27, B. longum PXN 30, Lb. acidophilus PXN 35, Lb. delbrueckii spp. bulgaricus PXN39, Lb. casei PXN 37, Lb. plantarum PXN 47, Lb. rhamnosus PXN 54, Lb.helveticus PXN 45, Lb. salivarius PXN 57, L. lactis PXN 63, S. thermophilus PXN 66; a total of 2.0 × 109 cfu/capsule) 4 capsules/d	Microcrystalline cellulose, hydroxypropyl methylcellulose4 capsules/d	16 weeks	Significantly improved IBS symptoms and their severity
Lee et al. (2018) [114]	The single-arm, open-label, pilot study	Rome III	11 males 19–70 y	IBS-D	Ther-Biotic® Complete (Lb. rhamnosus 6.0 × 109 cfu/capsule, B. bifidum 5.0 × 109 cfu/capsule, Lb. acidophilus 3.0 × 109 cfu/capsule, Lb. casei 2.5 × 109 cfu/capsule, Lb. plantarum 2.0 × 109 cfu/capsule, Lb. salivarius 2.0 × 109 cfu/capsule, B. longum 1.0 × 109 cfu/capsule, S. thermophilus 1.0 × 109 cfu/capsule, Lb. bulgaricus 1.0 × 109 cfu/capsule, Lb. paracasei 5.0 × 108 cfu/capsule, B. lactis 5.0 × 108 cfu/capsule, B. breve 5.0 × 108 cfu/capsule)	No placebo or control group	8 weeks	Ameliorated abdominal discomfort, dyspepsia, flatulence, and stool consistency Decreased SIBO prevalence Beneficial impact on GIT microbiota
Kim et al. (2018) [96]	The double-blind, randomized, placebo-controlled, parallel study	individual protocol	42 males/females 20–54 y	wd	Lb. gasseri BNR17 Low dose: 2 × 108 cfu/d 26 Medium dose: 2 × 109 cfu/d High dose: 2 × 5 × 109 cfu/d	Dextrin	7 days of the run-in period, then 4 weeks	Amelioration of IBS symptoms The abundance of probiotic strain in fecal samples of treated subjects The optimal dosage appeared to be high dose (2 × 5 × 109 cfu/d)
Majeed et al. (2018) [127]	The randomized, double-blind, placebo-controlled, multicenter, parallel-group clinical study	Rome III	40 males/females 20–65 y	wd	Microcrystalline cellulose, starch, sodium starch glycolate, magnesium stearate, 2.0 × 109 spores/tablet B. coagulans MTCC 5856 1 tablet/d	Microcrystalline cellulose, starch, sodium starch glycolate, magnesium stearate1 tablet/d	90 days of treatment, then 15 days of follow-up	Decrease in depression, along with diminished IBS symptoms Reduced sleeplessness Decreased serum levels of myeloperoxidase
Shin et al. (2018) [97]	The single-center, randomized, double-blind, placebo-controlled clinical trial	Rome III	51 males/females 20–55 y	IBS-D	Maltodextrin, microcrystalline cellulose, magnesium stearate, Lb. gasseri BNR17 (total of 1010 cfu/d) 4 capsules/d	Maltodextrin, microcrystalline cellulose, magnesium stearate4 capsules/d	8 weeks	Improved bowel habits (longer colon transit time) Positive impact on intestinal microbiota (decreased Firmicutes, increased Actinobacteria, and Bacteroidetes)
Sun et al. (2018) [105]	The prospective, multicenter, randomized, double-blind, placebo-controlled trial	Rome III criteria	200 males/females 18–65 y	IBS-D	1.5 × 107 cfu/capsule C. butyricum 9 capsules/d	No data on used compounds 9 capsules/d	4 weeks	Improvement in overall IBS symptoms and quality of patients’ life No significant changes in intestinal microbiota diversity Reduction of Clostridium sensu stricto in microbial community Improvement of alanine and tryptophan metabolism
Hong et al. (2019) [111]	Animal study	na	54 males C57L/B6 mice (15.5 ± 1.0 g) aged 4 weeks	na PI-IBS model (Trichinella)	Formulated probiotics (DW; Lb. acidophilus LA5, B. lactis BB12, S. boulardii) 0.2 mL of the solution of 5.0 × 109 cfu/g VSL#3 0.2 mL of the solution of 5.0 × 109 cfu/g	No data on used compounds 0.2 mL of the solution of 5.0 × 109 cfu/g	4 weeks	Decreased levels of serum pro-inflammatory cytokines in uninfected and infected mice treated with probiotics (DW and VSL#3) Diminished visceral hypersensitivity (DW)
Leventogiannis et al. (2019) [112]	Open-label clinical study	Rome III/SIBO-positive or SIBO-negative	Males/Females ≥ 18 y	All	Lactolevure® (1.5 × 109 cfu/capule S. boulardii, 1.75 × 109 cfu/capsule B. lactis BB-12, 1.5 × 109 cfu/capsule Lb. acidophilus LA-5, 5.0 × 108 cfu/capsule Lb. plantarum) 2 capsules/d	No placebo/control group	30 days	Amelioration of bloating More significant improvement of symptoms among IBS patients with SIBO Decreased abdominal pain severity
Madempudi et al. (2019) [103]	The randomized, double-blind, placebo-controlled trial	Rome III	108 males/females 18–60 y	wd	Excipient (maltodextrin), 2.0 × 109 cfu/capsule B. coagulans Unique IS2	Excipient (maltodextrin)	8 weeks	Relief in the severity of symptoms (bloating, incomplete evacuation, urgency, straining, the passage of gas, bowel habit satisfaction, and stool consistency) Reduced abdominal pain Increased number of complete spontaneous bowel movement
Oh et al. (2019) [124]	The randomized, double-blind, placebo-controlled trial	Rome III	50 males/females 19–60 y	With the exclusion of IBS-C	Foodis Lactobacillus—excipients (olive oil, pine oil), and Lb. paracasei, Lb. salivarius, 1 × 109 cfu/mL Lb. plantarum (ratio 5:4:1)	Excipients (olive oil, pine oil)	1 week screening period, then 4 weeks of treatment	Relief in global IBS symptoms Decreased severity of abdominal pain
Zhang et al. (2019) [125]	Pilot study	Rome III	15 males/females 18–65 y	IBS-D	Bifico® (B. longum, Lb. acidophilus, E. faecalis; a total of ≥1.0 × 107 cfu)20 mg 3 times a day	Antidepressant (Duloxetine) 30 mg/d for 4 days, then 60 mg/d	8 weeks	Changes in gut microbiota and SCFAs 27 concentrations (probiotic and antidepressant) Reduced severity of abdominal symptoms (probiotic and antidepressant) Decreased plasma levels of cytokines (probiotic and antidepressant)
Zhao et al. (2019) [106]	Animal studies	na	24 C57BL/6 male mice aged 6–8 weeks	na PI-IBS model (TNBS 28)	1 × 108 cfu/mL C. butyricum 200 µL/d	Saline	4 weeks of model preparation, one week of treatment	Attenuated intestinal visceral hypersensitivity Diminished low-grade mucosal inflammation (suppressed production of cytokines, decreased number of lamina propria dendritic cells)
Caviglia et al. (2020) [93]	The prospective study	Rome IV	16 males/females 16–65 y	IBS-D	B. longum ES1 1 × 109 cfu	Lack of control	8–12 weeks	Improvement in general IBS symptoms Amelioration of the immune-inflammatory condition (reduced cytokines, and zonulin levels) Increased integrity of the intestinal barrier
Lewis et al. (2020) [95]	The randomized, double-blind, placebo-controlled, 3-arm parallel-group study	Rome III	285 males/females ≥ 18 y	All	Excipients (potato starch, and magnesium stearate), and 10 × 109 cfu/capsule of B. longum HA-196, or Lb. paracasei R0175	Potato starch, and magnesium stearate	2-week run-in period, next 8 weeks of treatment	Significantly improved bowel habits, and stool consistency in IBS-D, and IBS-C subjects (Lb. paracasei R0175) The positive impact of social aspects of life (both probiotic strains) Increased number of Bifidobacterium ssp. in fecal samples (B. langum HA-196)No vital changes in A. muciniphila, and F. prausnitzii abundance Distinct placebo effect
Martoni et al. (2020) [92]	The randomized, double-blind, placebo-controlled, multicenter study	Rome IV	336 males/females 18–70 y	wd	Microcrystalline cellulose, and ≥1 × 1010 cfu/capsule of Lb. acidophilus DDS®-1, or B. animalis subsp. lactis UABla-12™ 1 capsule/d	Microcrystalline cellulose 1 capsule/d	2-week run-in period (only placebo), 6 weeks of treatment (probiotic/placebo)	Improvement in stool consistency Reduced abdominal pain severity Vital amelioration of IBS symptoms Diminished stress levels (Lb. acidophilus DDS®-1)
Zhou et al. (2020) [94]	Animal study	na	Male Sprague-Dawley rats (weight: 225~260 g)	na WAS model	B. longum 1 × 109 cfu/mL once a day	0.9% saline	10 days	Influenced Paneth cells function—enhanced lysozyme production, and repair of mucus No difference in serum cytokines levels Beneficial alteration of GIT microbiota Improved intestinal permeability
Gupta et al. (2021) [104]	The prospective, interventional, randomized, double-blind, placebo-controlled clinical study	Rome IV	40 males/females 18–65 y	wd	Excipient with B. coagulans LBSC 2 × 109 spores/sachet 3 sachets/d 29	Excipient with maltodextrin 3 sachets/d	Up to 80 days	Improvement in abdominal symptoms (pain, stomach rumbling) Attenuation of bloating, cramping, nausea, vomiting, diarrhea, anxiety Beneficial modulation of GIT microbiota Amelioration in stool consistency
Seong et al. (2021) [99]	Animal study	na	14 male Wistar rats (weight: 304 ± 1.4 g) aged 8 weeks	na IBS induced by chronic restraint stress	Maltodextrin and heat-killed 1 × 1011 cfu Lb. casei DKGF7	Maltodextrin	4 weeks	Improvement of IBS symptoms in the animal model Decrease in serum corticosterone levels, inflammatory cytokines in colonic tissue Enhanced expression of tight junction proteins
Skrzydło-Radomańska et al. (2021) [126]	The randomized, double-blind, placebo-controlled, parallel-group trial	Rome III	51 males/females 8–75 y	IBS-D	NordBiotic™ (B. breve BB010 B. longum BL020, B. bifidum BF030, B. lactis BL040, Lb. rhamnosus LR110, Lb paracasei LPC100, Lb acidophilus LA120, Lb. casei LC130, Lb plantarum LP140, S. thermophilus ST250; Total 2.5 × 109 cfu/capsule) 2 capsules/d	Maltodextrin 2 capsules/d	8 weeks	Improved quality of patients’ life Diminished severity of abdominal pain

¹ the final (after screening) number of participants who received treatment is given; ² years old; ³ without differentiation; ⁴ colony-forming units per milliliter, ⁵ milliliters per day; ⁶ capsules per day; ⁷ not applicable; ⁸ small intestinal bacterial overgrowth; ⁹ early rise in breath hydrogen after lactulose; ¹⁰ colony-forming units per packet; ¹¹ packets per day; ¹² colony-forming unit per capsule; ¹³ colony-forming units per gram; ¹⁴ cells per day; ¹⁵ milligrams per day; ¹⁶ post-infection IBS; ¹⁷ post-antibiotic IBS; ¹⁸ tablets per day; ¹⁹ colony-forming units per cup; ²⁰ cups per day; ²¹ interleukins; ²² tumor necrosis factor α; ²³ milliliters per kilogram; ²⁴ spores per gram; ²⁵ spores per tablet; ²⁶ colony-forming units per day; ²⁷ short-chain fatty acids; ²⁸ 2,4,6-trinitrobenzenesulfonic acid; ²⁹ sachets per day.