For many years, psychiatry primarily explained disorders such as depression, anxiety, and schizophrenia through imbalances in brain chemicals. However, recent research has revealed that the trillions of microorganisms residing in our digestive system—known as the gut microbiota—may have a far more profound impact on mental health than previously thought. These microorganisms do more than regulate digestion; they influence the production of neurotransmitters such as serotonin, dopamine, and GABA, which directly affect brain function. Remarkably, approximately 90% of the body’s serotonin is produced in the gut.
Communication between the gut and the brain occurs through several pathways. Via the vagus nerve, signals from the gut are transmitted directly to the brain. Animal studies have shown that certain bacteria reduce anxiety only when the vagus nerve is intact. Chemically, the microbiota influences neurotransmitter production, while the immune system pathway allows imbalances in the gut—known as dysbiosis—to trigger chronic inflammation, which is linked to psychiatric disorders such as depression and schizophrenia. This demonstrates how even minor disturbances in the gut can significantly affect brain function.
The relationship between the microbiota and psychiatric disorders is increasingly recognized. In depression, studies have found reduced diversity in the gut flora compared to healthy individuals, and probiotic supplementation has sometimes alleviated depressive symptoms. In anxiety disorders, species such as Lactobacillus and Bifidobacterium have shown anxiolytic effects. In schizophrenia, gut bacteria appear to influence dopamine metabolism, potentially affecting the course of the disorder. In autism spectrum disorder, alterations in gut microbiota have been observed, and certain probiotic interventions have shown improvements in social behaviors and repetitive actions.
The emerging concept of “psychobiotics” refers to probiotics that have a positive effect on mental health. For example, Lactobacillus rhamnosus has been shown in animal studies to reduce anxiety, while Bifidobacterium longum can alleviate depressive symptoms. These findings suggest that psychobiotics may, in the future, serve as complementary or alternative treatments to conventional antidepressants.
In daily life, supporting the gut-brain axis involves consuming a diet rich in fiber, minimizing processed and additive-laden foods, maintaining regular sleep, and engaging in physical activity. These practices not only support gut health but also positively influence mental well-being.
The gut microbiota is not merely a system for digestion; it is a powerful biological mechanism that influences brain function and mood. Disorders such as depression, anxiety, schizophrenia, and autism may involve both chemical imbalances in the brain and disruptions in gut health. In the future, psychiatry is expected to increasingly incorporate multi-dimensional treatment approaches that combine medication, nutrition, probiotic supplementation, and inflammation management.
