Abstract
The balance between physiological, psychological, and environmental factors often shapes human experience. In recent years, research has drawn attention to the gut microbiota as a significant contributor to brain function and emotional regulation. This narrative review examines how changes in gut microbiota may relate to depression. We selected studies that explore the link between intestinal dysbiosis and mood, focusing on mechanisms such as inflammation, vagus nerve signaling, HPA axis activation, gut permeability, and neurotransmitter balance. Most of the available data come from animal models, but findings from human studies suggest similar patterns. Findings are somewhat difficult to compare due to differences in measurement procedures and patient groups. However, several microbial shifts have been observed in people with depressive symptoms, and trials with probiotics or fecal microbiota transplant show potential. These results remain limited. We argue that these interventions deserve more attention, especially in cases of treatment-resistant or inflammation-driven depression. Understanding how the gut and brain interact could help define clearer subtypes of depression and guide new treatment approaches.