Table 4.

Research studies investigating the relationship between the gut microbiota and gastrointestinal symptoms.

Model/cohort	Findings	Reference
IBS patients	- Microbial signatures clustered into two groups: normal microbiota vs. increased F/B ratio.	Jeffery et al. (2012)
	- IBS with normal microbiota were more likely to have depression.
	- Suggests potential differing triggers for IBS-like symptoms.
IBS patients and MD mouse model (male)	- FMT from IBS patients to MD-mice transferred phenotype.	Ge et al. (2017)
	- SCFAs and secondary bile acids were subsequently decreased in recipient mice.
IBS patients and GF mouse model	- FMT from IBS patients to GF-mice transferred phenotype including intestinal barrier dysfunction, innate immune activation, and anxiety-like behaviour.	De Palma et al. (2017)
IBS patients and healthy donor	- FMT from healthy donor to IBS patients reduced abdominal pain symptoms and increased α- and β-diversities.	Cruz-Aguliar et al. (2019)
	- Patients with microbiota mostly like the donor had the greatest reduction in pain.
	- Abundance of Akkermansia muciniphila inversely correlated with pain intensity.
Review – multiple cohorts	- Potential influence of Lactobacillaceae and Bacteroides metabolites on inflammation and bloating.	Pittayanon et al. (2019)
IBS patients	- Significant differences in microbiome and metabolome profiles compared to controls.	Jeffery et al. (2020)
	- Faecal metabolomes could differentiate IBS patients with and without bile acid malabsorption.
	- Decreased bacterial diversity.
Meta-analysis of IBS patients	- FMT from healthy donors significantly decreased IBS symptoms and improved QoL.	Wang et al. (2023)
Meta-analysis of IBS patients	- FMT from healthy donors significantly decreased IBS symptoms but decreased QoL.	Halkjær et al. (2023)
Review of IBS patients	- Increased F/B ratio in IBS.	Shaikh et al. (2023)
	- No specific microbial signature.

FMT, faecal microbiota transfer; IBS, irritable bowel syndrome; SCFA, short-chain fatty acid; QoL, quality of life.