Baseline intestinal microbiota composition influences response to a real-world dietary fiber intervention

The intestinal microbiota is shaped by fiber-rich ingredients, such as unripe banana flour (UBF), high in resistant starch (RS). We investigated the effects of RS-rich UBF and inulin on gut microbiota and intestinal function in a double-blind, randomized, placebo-controlled pilot trial. Forty-eight healthy adults consumed maltodextrin (control), inulin, or UBF three times weekly for six weeks. Microbiota composition and function were analyzed using 16S rRNA gene sequencing and PICRUSt, alongside fecal short-chain fatty acids, blood biochemistry, and gastrointestinal parameters. We observed two microbiota clusters at baseline, one Prevotella-rich (P) and one Bacteroides-rich (B), with distinct responses to the interventions. Only cluster P subjects consuming UBF showed significant global microbiota shifts (weighted Unifrac Beta diversity, PERMANOVA p = 0.007) and major functional changes (533 KEGG orthologs, FDR < 0.05). Inulin produced modest modulation (19 KOs) on cluster P, and no effects were observed on cluster B. RS-rich UBF modulated gut microbiota in a composition-dependent manner, supporting the potential of microbiota-based stratification to improve dietary fiber interventions.