Dietary Modulation of Gut Microbiota in Obesity and Type 2 Diabetes: A Narrative Review

Abstract

Obesity and type 2 diabetes mellitus (T2DM) are major metabolic disorders shaped by interactions among diet, host physiology, and the gut microbiota. Growing human evidence indicates that dietary fiber, prebiotics, probiotics, synbiotics, polyphenols, fermented foods, and Mediterranean-style dietary patterns can alter microbial composition and function, with potential effects on short-chain fatty-acid production, intestinal barrier integrity, inflammatory signaling, and glucose homeostasis. This narrative review synthesizes human clinical and mechanistic evidence on dietary modulation of the gut microbiota in obesity and T2DM, with a structured literature update through September 2026. Recent systematic reviews and meta-analyses suggest that microbiota-targeted dietary interventions can produce modest improvements in glycemic and inflammatory outcomes, but effects on microbial diversity, body weight, and specific taxa remain heterogeneous. Inter-individual variation in baseline microbiota, intervention composition and dose, medication use, geographic dietary patterns, sequencing methods, and study duration limits direct comparison across trials. Emerging evidence supports a shift from universal microbiome-targeted recommendations toward food-based and precision-nutrition approaches that account for microbial and metabolic phenotype. Well-powered, longer-duration randomized trials using harmonized microbiome and metabolomic methods are needed before specific microbial signatures can be routinely used to guide clinical nutrition practice.