Abstract
Type 2 diabetes mellitus (T2DM) is a complex metabolic disorder influenced not only by genetics, diet, and lifestyle but also by the gut microbiota. Dysbiosis (imbalances in microbial composition) can disrupt gut barrier integrity, alter microbial metabolites, and trigger low-grade inflammation, contributing to insulin resistance and β-cell dysfunction. Nutritional interventions, such as probiotics, prebiotics, synbiotics, postbiotics, and bioactive food components, represent potential therapeutic approaches for ameliorating gut eubiosis and advancing glycemic regulation. This narrative review incorporates evidence from selected studies identified by searches in PubMed, Scopus, and Google Scholar for studies published up to November 2025. The methodology included a structured literature search of in vitro, animal, and human studies, with a focus on intervention trials and mechanistic research. There are many positive signals from randomized controlled trials (RCTs), but heterogeneity and short follow-up limit definitive recommendations. Evidence from clinical and experimental studies indicates a beneficial effect on fasting glucose, hemoglobin A1c, and inflammatory markers, though heterogeneity of the individual and the variability in study designs limit generalization. There is insufficient evidence to recommend microbiota modulation as standard therapy in any disease. Key knowledge gaps include standardized interventions, stratified analyses by medication use (e.g., metformin), clinically meaningful endpoints, and long-term safety data. This review summarizes current knowledge on gut microbiota-driven mechanisms in T2DM and evaluates emerging microbiota-targeted therapies as adjunctive strategies for metabolic improvement.