Table 2:

Characteristics and Findings of Studies Evaluating Gut Microbiome Composition as a Predictor of low Fermentable Oligosaccharide Disaccharide Monosaccharide and Polyol diet efficacy for Irritable Bowel Syndrome

Reference	IBS Population studied	Study Design	Diet Responder Definition	Microbiome Analysis	Discriminant Analysis	Key Baseline Microbiome Findings
Chumpitazi et al.12	Children (ages 7–17 years), n=8	Open-label: low FODMAP × 1 week	≥50% decrease in abdominal pain frequency from baseline	16s rRNA pyro-sequencing	Yes: LEfSE	Responders (n=4) enriched in Sporobacter, Subdoligranulum, Alistipes, and an unclassified Ruminococcaceae. Non-responders (n=4) enriched in Bacteriodes, unclassified Bacteriodales, and a different unclassified Ruminococcaceae.
Halmos et al.10	Adults, n=30	Cross-over RCT (low FODMAP vs. Australian diet) × 21 days	10 mm decrease in visual analogue scale	Select PCR probes of total bacteria and 9 specific targets	No	No differences between Responders (n=21) vs. Non-responders (n=9).
Chumpitazi et al.11	Children, n=33	Cross-over RCT Low FODMAP vs. Typical American childhood diet × 48 hours	50% decrease in abdominal pain frequency during the low FODMAP diet alone.	16s rRNA pyro-sequencing	Yes: LEfSE	Responders (n=8) were enriched in 63 microbial OTUs including: Bacteriodes, Ruminococcaceae, F. prausnitzii, Dorea and Clostridiales. Nonresponders (n=15) were uniquely enriched in Turicibacter. Placebo-responders (n=10) not included.
Bennet et al.49	Adults, n=31 placed on low FODMAP	Parallel group RCT (low FODMAP vs. traditional IBS diet) × 4 weeks	Reduced IBS-Symptom Severity Score by ≥ 50	54 DNA probes targeting ≥ 300 bacteria. Calculation of Dysbiosis Index.	Yes: Multivariate factor orthogonal partial least square discriminant analysis	No bacteria found to be enriched in Responders (n=19). Nonresponders (n=12) enriched in several bacteria including Bacteroides stercoris, Parabacteriodes, Bacillus, Pseudomonas, Acineteobacter, Desulfitispora, Streptococcus, Dorea, Ruminococcus gnavus. Nonresponders had a higher dysbiosis index score at baseline.
Valeur et al.48	Adults, n=61	Open-label, 4 week FODMAP restriction	50% reduction in IBS-Symptom Severity Score	54 DNA probes targeting ≥ 300 bacteria. Calculation of Dysbiosis Index.	No	Responders (n=32) were enriched in Bacteroides fragilis, Acinetobacter, Ruminiclostridium, Streptococcus, and Eubacterium. Nonresponders (n=29) were enriched in Clostridia, Negativicutes, Bacilli; Actinomycetales, Anaerotruncus; Clostridiales; and Shigella, Escherichia. No difference in dysbiosis index between Responders and Nonresponders.

IBS= irritable bowel syndrome; RCT = randomized controlled trial; LEfSE= Linear Discriminant Analysis Effect Size; OTU = operational taxonomic unit