Dietary modulation of the gut microbiota in type 2 diabetes and obesity: mechanisms, interventions, and clinical perspectives

Obesity and type 2 diabetes mellitus (T2DM) are associated with heterogeneous changes in gut microbial composition and function, while mechanistic studies support plausible links among diet, microbial metabolism, intestinal barrier function, immune signaling, and host metabolism. This narrative review integrates diet-microbiome mechanisms, dietary-assessment and multi-omics methodology, major dietary patterns, quantitative clinical intervention evidence, treatment-related microbiome modulation, and implications for precision nutrition. High-fiber, Mediterranean, plant-based, and Western-style dietary patterns can modify microbial functions and metabolites, but responses vary across populations, substrates, baseline microbiota, medications, and study methods. Randomized trials and meta-analyses show selected metabolic effects of dietary and microbiome-targeted interventions; effects are generally modest and heterogeneous, and prebiotics, probiotics, synbiotics, and postbiotics are not interchangeable across products or populations. Medication and procedural exposures can also alter microbiome and metabolome readouts and confound interpretation. Current evidence does not provide a validated basis for routine microbiome-guided pharmacological or surgical treatment selection. Integration of dietary, microbiome, metabolome, and clinical data may identify metabotypes and candidate response patterns, but individualized microbiome-based nutrition remains an emerging, validation-dependent research domain rather than routine clinical practice.