Short-chain fructo-oligosaccharides modulate gut microbiota composition and metabolism: dose–response assessment in an ex vivo gut model

Short-chain fructo-oligosaccharides (scFOS) are prebiotic fiber rapidly fermented in the colon and known to stimulate beneficial bacteria, such as Bifidobacterium spp. and Lactobacillaceae. While their overall effects on the gut microbiota are established, the dose–response relationship remained only partially characterized. This study aimed to determine the minimum effective dose of scFOS required to modulate gut microbiota composition and functions. An ex vivo chemostat model was used to simulate colonic fermentation with different doses of scFOS (1 to 10 g/d). Microbiota composition and metabolic activity were assessed by qPCR, short-chain fatty acid (SCFA) quantification, and shotgun metagenomics. An increase in scFOS dose led to higher SCFA levels, particularly acetate and butyrate, along with a modification in microbial composition, with a minimum significant effective dose of 2.5 g/d. Significant increase in Bifidobacterium adolescentis, Anaerostipes hadrus, and Clostridium innocuum was observed at the same dose. Functional analysis revealed an enrichment of GH32 genes in the pangenomes of species positively impacted by scFOS. These findings demonstrate that low doses of scFOS can effectively modulate the gut microbiota and enhance SCFA production, supporting their use in dietary interventions aimed at improving intestinal health.