Anxiety and depression are among the most common mental health problems worldwide, affecting people’s daily lives, relationships, and overall well-being. Traditionally, these conditions have been explained mainly in terms of chemical imbalances in the brain and psychological stress. However, in recent years, researchers have started to look beyond the brain and have found that the gut microbiota also plays an important role in mental health. The gut microbiota consists of a large number of microorganisms living in the digestive system, and it communicates with the brain through what is known as the gut–brain axis. This communication happens through several pathways, including neural, immune, hormonal, and biochemical mechanisms. This paper examines how changes in gut microbiota, known as dysbiosis, are linked to anxiety and depression. It highlights that people with these conditions often show reduced diversity of gut bacteria, an increase in harmful or inflammation-causing microbes, and a decrease in beneficial bacteria that produce important substances like short-chain fatty acids. These changes can affect the body in several ways, such as increasing gut permeability, causing inflammation, and disturbing the production of neurotransmitters and stress hormones. The paper also explains how the gut and brain interact through different mechanisms, including signals sent via the vagus nerve, immune system activity, and the regulation of the body’s stress response system (HPA axis). From a psychological point of view, these biological changes can influence mood, emotional control, stress handling, memory, and motivation. In addition, the study discusses possible treatment approaches that focus on improving gut health, such as probiotics, prebiotics, dietary changes, and fecal microbiota transplantation. While these approaches show potential, especially for depression, the results are not always consistent, particularly in the case of anxiety, and more research is needed. Overall, the findings suggest that gut microbiota plays an important role in mental health. Understanding this connection may help in developing better and more personalized treatment strategies by combining both biological and psychological approaches.

Keywords— Gut Microbiota , Gut–Brain Axis , Dysbiosis , Anxiety and Depression , Psychobiotics