Structural diversity of dietary carbohydrates shapes gut microbiota, digestive physiology, incretin hormones, and systemic metabolic health

Dietary carbohydrates, including simple sugars, starches, and dietary fibers, play a crucial role in governing gastrointestinal digestion, gut microbial ecology, endocrine signaling, and overall metabolic balance. New evidence suggests that the physiological effects of carbohydrates depend not only on their intake but also on their structural features, such as glycosidic linkages, molecular weight, degree of polymerization, branching patterns, crystallinity, and chemical modifications. This review emphasizes current understanding of how structural differences in dietary carbohydrates impact digestion, gut microbiota composition, and host metabolic responses. Recent mechanistic, experimental, and clinical studies were reviewed to examine how carbohydrate structures interact with microbial fermentation and host metabolic signaling pathways. Evidence indicates that structural traits influence enzymatic digestibility and fermentation rates in the gastrointestinal tract, thereby affecting metabolite production, such as short-chain fatty acids (SCFAs), and interactions with bile acids. These processes subsequently affect enteroendocrine pathways involving incretins, like glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), as well as satiety hormones such as peptide YY (PYY). Additionally, slowly digestible starch, resistant starch, and fermentable soluble fibers can reduce post-meal blood sugar spikes, modify gut microbiota profiles, and support overall metabolic health. Microbial enzymes that break down carbohydrates and polysaccharide utilization loci further influence host–microbiota interactions. Although increasing evidence supports these connections, key gaps remain in linking specific carbohydrate structural features with targeted microbial responses and metabolic outcomes. Closing these gaps could enable the development of tailored dietary strategies and functional foods to improve metabolic health.