TABLE 2.

Studies of gastrointestinal microbiota metabolites and their effects.

Ref	Metabolites	Primary sources	Effects
Markowiak-Kopeć and Śliżewska, (2020); Serpa et al., (2010); Haveaar, (2011)	ScFAs (formic acid, acetic acid, propionic acid, butyric acid)	The Clostridium group of Firmicutes phylum, and Lactobacillus, Bifidobacterium, Eubacteriaceae, Fecal bacteria	Regulation of the pH value in the intestine; Promoting the absorption of water, sodium, calcium, magnesium and other substances; Inhibiting the multiplication and growth of pathogenic bacteria and the activity of intestinal inflammatory mediator; Maintaining the integrity of gap junctions in the intestine.
Alexandrov et al. (2020)	Lipid (cholesterol, LPS, peptidoglycan)	Bifidobacterium, Lactobacillus, Enterobacteriaceae and Clostridium	Regulation of the intestinal permeability and intestinal immunity; Disruption of the body’s immune system and induction of inflammatory responses.
Brown et al. (2019)	Lipid (sphingolipids)	Bacteroidetes and Prevotellaceae	Aggravating intestinal inflammation
Gao et al., (2019); Gao et al. (2020)	Indole-derived (tryptophan)	Clostridium sporogenes and Escherichia coli	Regulation of the brain-gut axis and protection against stress-induced damage in the gastrointestinal tract