Gut microbiota and constipation: from causal evidence to therapeutic strategies-a state-of-the-art narrative review.

Constipation is a common functional disorder of the gastrointestinal tract with a global prevalence of approximately 10-20%, which seriously affects patients' quality of life and imposes a heavy socioeconomic burden. In recent years, the role of the gut microbiota in the pathogenesis of constipation has received increasing attention, particularly in the context of the brain-gut axis theory. In this narrative review, we critically examine the research literature on constipation and intestinal microecology published over the past decade, focusing on four aspects: (1) the characteristics of the gut microbiota in patients with constipation, including changes in microbial diversity, alterations in the abundance of specific taxa, and differences across constipation subtypes; (2) Mendelian randomization studies that provide genetic-level evidence consistent with the hypothesis that certain microbiota alterations may precede constipation rather than merely result from it; (3) mechanisms of microbiota-host interactions mediated by the brain-gut axis, with an emphasis on neural, metabolic and immune pathways; and (4) microbiota-based intervention strategies (probiotics, prebiotics, synbiotics, postbiotics and fecal microbiota transplantation) and their clinical evidence. Our findings suggest that specific microbiota alterations may contribute to constipation pathophysiology and the promise of personalized, microbiome-based therapies. Although microbiota-based interventions show potential therapeutic value in selected patients, current evidence is limited by substantial heterogeneity in study design, small sample sizes, inconsistent microbiome signatures, and limited long-term safety data. High-quality evidence from large, well-designed RCTs is lacking for most interventions, and findings from low-certainty studies (e.g., conference abstracts, animal experiments, small uncontrolled trials) should be interpreted as preliminary and hypothesis-generating rather than conclusive. Therefore, microbiota-targeted therapies should currently be considered exploratory or adjunctive rather than established standard treatments for constipation. Future progress will require standardized methodologies, mechanistic validation studies, and phenotype-stratified clinical trials to support translation toward precision microbiome-based medicine.