Over the past two decades, accumulating evidence has demonstrated bidirectional communication between the gastrointestinal tract and the central nervous system, commonly referred to as the gut–brain axis. This complex network integrates neural, hormonal, immunological, and metabolic pathways and plays a critical role in maintaining both physiological and psychological homeostasis. Increasing attention has been directed toward its involvement in mood and anxiety disorders, which constitute a major global public health challenge. This narrative review aims to synthesise current human-based research examining gut–brain axis dysfunction in mood and anxiety disorders, with particular emphasis on underlying pathophysiological mechanisms, diagnostic challenges, and emerging therapeutic strategies. A comprehensive literature search was conducted using PubMed, Scopus, and Web of Science, focusing on original clinical, neuroimaging, and translational studies published between 2000 and 2025. The available evidence indicates that alterations in gut microbiota composition, increased intestinal permeability, immune system activation, and changes in microbial metabolite production are consistently associated with depressive and anxiety-related symptoms. Moreover, the high prevalence of psychiatric comorbidity observed in functional and inflammatory gastrointestinal disorders supports the existence of shared biological pathways. Despite significant advances, the clinical translation of gut–brain research remains limited by the lack of standardised diagnostic tools and validated biomarkers. This review highlights the therapeutic potential of novel interventions, including psychobiotics, dietary modifications, and microbiota-targeted therapies, while emphasising the need for interdisciplinary collaboration and further human studies to support their integration into routine clinical practice.
Olewińska et al. (Mon,) studied this question.