The microbiota-gut-brain axis perspective: mechanisms and intervention strategies for the comorbidity of chronic constipation and depression

Background: Chronic constipation and depression are highly prevalent worldwide. These two conditions frequently co-occur in clinical practice. Accumulating evidence indicates that gut microbiota dysbiosis mediates this comorbidity through the microbiota-gut-brain axis (MGBA). Methods: This narrative review systematically summarizes current research on MGBA bidirectional communication mechanisms, gut microbiota alterations in comorbid patients, and microbiota-targeted intervention strategies. Results: The MGBA facilitates bidirectional communication through four major pathways: neural pathways via the vagus nerve, immune pathways via cytokines, endocrine pathways via the HPA axis, and metabolic pathways via short-chain fatty acids and neurotransmitter precursors. Gut dysbiosis is associated with comorbidity and may contribute to its pathogenesis through multiple mechanisms. First, neurotransmitter metabolism becomes dysregulated, particularly in the serotonin and GABA systems. Second, chronic low-grade inflammation develops with elevated pro-inflammatory cytokines. Third, intestinal barrier dysfunction occurs, leading to increased permeability and bacterial translocation. Fourth, HPA axis hyperactivity emerges. Fifth, production of microbial metabolites is altered, including short-chain fatty acids and tryptophan metabolites. Comorbid patients exhibit characteristic microbiota signatures. These include reduced abundance of butyrate-producing bacteria such as Faecalibacterium, Roseburia, and Coprococcus. Microbial diversity decreases significantly. Pro-inflammatory taxa become enriched. Several evidence-based interventions show promise. These include psychobiotics, fecal microbiota transplantation, and dietary modifications such as Mediterranean diet and high-fiber intake. Exercise and integrative approaches including traditional Chinese medicine also demonstrate beneficial effects. Conclusion: The gut microbiota represents a critical hub connecting gastrointestinal and mental health. Microbiota-targeted therapies offer promising strategies for managing chronic constipation-depression comorbidity. Future research should establish causal relationships and develop reliable microbial biomarkers. Precision medicine approaches based on individual microbiome profiles are needed to optimize therapeutic outcomes.