From Dysbiosis to systemic health: Microbiome modulation as a unified therapeutic framework.

The gut microbiome is a dynamic microbial ecosystem regulating gastrointestinal, metabolic, immune, and neurobehavioral physiology. Dysbiosis has been linked to irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and systemic disorders including metabolic syndrome, autoimmune conditions, and neurodegenerative diseases. This narrative review synthesizes mechanistic, clinical, and translational evidence to delineate molecular pathways of microbiome-targeted interventions, evaluates clinical outcomes in IBS and IBD, and proposes a unified framework linking gastrointestinal modulation to systemic health. A structured literature search across PubMed/MEDLINE, Scopus, Web of Science, and Google Scholar (2012-2024) identified approximately 68 eligible sources, appraised using Cochrane Risk of Bias 2.0 and AMSTAR-2. Five principal molecular pathways were identified: competitive pathogen exclusion, epithelial barrier reinforcement, immune modulation, short-chain fatty acid (SCFA) production, and neurotransmitter signaling. Clinically, dietary strategies, biological agents (probiotics, prebiotics, synbiotics, postbiotics, and fecal microbiota transplantation [FMT]), advanced modalities (rifaximin, psychobiotics, bacteriophage therapy), and lifestyle interventions collectively engage these pathways. The same mechanisms underpin emerging applications in metabolic, autoimmune, neurological, and cardiovascular disease. We propose a three-tier model progressing from molecular mechanisms through gastrointestinal outcomes to systemic benefits, with precision medicine and standardized trial designs as prerequisites for therapeutic translation.