Introduction: Dietary interventions are central to the management of obesity, insulin resistance, type 2 diabetes and related cardiometabolic disorders, yet clinical responses vary substantially between individuals exposed to apparently similar nutritional prescriptions. The gut microbiota may explain part of this variability because it transforms dietary substrates into bioactive metabolites and influences intestinal, immune and endocrine pathways. Methods: A narrative review informed by a structured literature search was conducted using PubMed, ScienceDirect and Google Scholar. Search terms combined concepts related to gut microbiota, intestinal microbiota, dietary intervention, nutrition, fiber, prebiotics, probiotics, metabolic response, obesity, insulin sensitivity and glycemic response. Forty records were initially identified, and 21 references were retained for qualitative synthesis after duplicate removal, screening and full-text eligibility assessment. Results: The reviewed literature indicates that baseline microbial diversity, community structure and functional capacity are associated with differential metabolic responses to calorie restriction, fiber-rich dietary patterns, probiotics, prebiotics and glycemia-oriented personalized nutrition. Key taxa and communities discussed in the evidence include Bacteroides, Prevotella, Akkermansia muciniphila, Bifidobacterium, Lactobacillus and Christensenella-associated communities. Mechanistic pathways include short-chain fatty acid generation, bile acid transformation, tryptophan-derived signaling, incretin-related pathways, epithelial barrier integrity and low-grade inflammation. Conclusion: The gut microbiota should be regarded as both a biomarker and a potential mediator of response to dietary interventions. Microbiota-informed nutrition is promising for precision diabetes and endocrinology care, but standardized prospective studies integrating microbiome profiling with robust metabolic outcomes remain necessary before routine clinical implementation.