Depression is one of the leading causes of disability worldwide. While cognitive therapy and antidepressants that increase serotonin can be effective treatments for depression, these treatments don’t work for more than a third of depressed patients. More recent theories of depression suggest that an imbalance in gut microbiota and dysfunction in the axis connecting the gut and the brain may be involved. Aspects of modern life such as high stress, diets high in processed food, antibiotics, pesticides, and sanitized, urban environments have decreased both the amount and richness of healthy gut microbiota, while increasing the level of unhealthy microorganisms. Depressed patients show a different profile of gut microbiota from healthy people.
Some new treatments for depression are designed to regulate gut microbiota. The brain and gut may communicate via the vagus nerve, a large nerve that travels throughout the body. Probiotics have been shown in animal studies to reduce inflammatory cytokines. Omega-3 supplements can beneficially affect the composition of gut microbiota and increase the production of anti-inflammatory compounds. New theories of depression emphasize the role of leaky gut leading to chronic inflammation, gut microbiota, and gut-brain axis dysfunction in depression.