Resistant starch and diabetes-associated cognitive dysfunction: structure-dependent fermentation and gut-brain framework

Diabetes-associated cognitive dysfunction (DACD) affects memory, executive function, attention, and processing speed through interacting metabolic, vascular, inflammatory, and neural disturbances. Human observational studies show heterogeneous microbial profiles and associations between circulating short-chain fatty acids (SCFAs), particularly acetate, and cognitive status, although causal relationships remain unestablished. Resistant starch (RS) escapes small-intestinal digestion and is fermented in the colon. Differences among RS1–RS5 in physical accessibility, crystallinity, retrogradation, chemical modification, and lipid complexation determine microbial access and fermentation kinetics. Fermentation produces an integrated acetate–propionate–butyrate response: acetate supports cross-feeding, propionate contributes to FFAR2/FFAR3 and hepatic signaling, and butyrate links colonocyte energetics with epithelial, immune, and histone deacetylase-dependent pathways. This narrative Mini Review integrates human DACD observations, controlled RS feeding studies, and mechanistic animal evidence within a structure-dependent microbiota-gut-brain framework. The available evidence indicates that RS responses are conditioned by substrate structure, food matrix, and baseline degraders and cross-feeders, providing a basis for responder stratification. We therefore propose a proof-of-concept design using a chemically and physically specified RS, longitudinal microbiome and fecal/circulating SCFA profiling, separate intestinal and cerebrovascular measures, and multidomain cognitive outcomes. RS efficacy for cognitive outcomes in DACD remains unestablished, but RS offers a food-compatible and experimentally controllable platform for determining whether a reproducible microbial-metabolite response can modify cognition-relevant pathways in diabetes.