The Dose-Dependent Influence of Type 2 Resistant Starch on Gut Microbial Communities and Metabolic Outputs: An In Vitro Simulation

This study systematically investigated the dose–response relationship of resistant starch type 2 (RS2; Hi-maize 260; 0–15 g/L) on gut microbial composition, short-chain fatty acid (SCFA)/gas output, and tryptophan catabolism using an in vitro fermentation model. The highest RS2 concentration (15 g/L) elicited optimal metabolic outcomes, including maximal SCFA production; significant H2S reduction; and redirected tryptophan metabolism from potentially detrimental indoles toward neuroprotective metabolites. Microbial profiling revealed dose-dependent enrichment of saccharolytic taxa (Bifidobacterium,Lactobacillus) with concomitant suppression of proteolytic pathobionts (e.g.,Escherichia-Shigella). Correlation analyses revealed strong positive associations between beneficial microbes and both SCFAs and neuroprotective metabolites, whereas pathogenic taxa correlated inversely with these compounds. Collectively, these findings establish that functionally relevant microbiome modulation requires a sufficiently high, dose-tailored intake of RS2, providing a rational basis for precision dietary strategies aimed at improving host metabolic and gut health.