Major Depressive Disorder

Depression is a mental health condition where symptoms include lack of interest in life, insomnia, and even suicidal thoughts. Major depressive disorder is a clinical condition with prolonged symptoms of depression which occurs most commonly due to inflammation of the nervous tissue. This condition severely affects the quality of life of an individual. In 2017, there were 25.8 million cases of depression worldwide, of which nearly 94% had major depressive disorder. The cause of depression is complex, with multiple factors playing a role, for example chemical imbalance, stress, medications and even genetics.

Microbiota-Gut-Brain Axis

Along with the factors described above, the authors of the article explain how, in the last couple of decades, there have been studies showing a strong correlation between microorganisms in the gut (microbiota), brain health and depression. The composition of the microorganisms differs between individuals and is dependent on their nutrition intake. Therefore, it becomes important to personalize the nutrition treatment for each person, taking into account their pre-existing microbiota composition, their general diet and their body and brain functions. Hence, to combat major depressive disorder, the authors have proposed five main ways in which the microbiota can help.

How Can Gut Microorganisms Help Depression?

• Improving richness of gut microbiota: Nutrition can directly affect and help the growth of a diverse and healthy community of microorganisms. A ‘westernized diet’ (rich in animal proteins and sugar) is associated with stress, depression, and low microbiota diversity. Whereas a ‘non-westernized diet’, which is rich in fibers, causes microorganisms to release important molecules that act as messengers between the gut and the brain, and improve mental and gut health. The authors report that a study found that when patients with depression consumed a Mediterranean diet for 12 weeks, their depressive symptoms reduced when compared to patients with only social support.
• Promoting stress resilience: Stress is one of the main factors in depression. Certain bacteria are known to promote stress, versus others that are known to make body resilient to stress. Therefore, shifting the microbiota towards these stress-resilient promoting microorganisms using a personalized nutrition plan can help combat depression.
• Modulating the immunity: Inflammatory components of the immune system are associated with depression. Molecules released by certain gut microorganisms are known to reduce the production of these inflammatory components. Promoting these microorganisms through personalized nutrition is important.
• Maintaining strong gut outer layer barrier: The gut microorganisms, both good and bad, need to remain within the gut and must be prevented from leaking into the blood stream. Some bacteria, if in the blood stream or the central nervous system, will induce an inflammatory response, which can cascade into behavioral changes related to depression. To prevent the gut microorganisms from leaking out of the gut, a healthy gut and a high-fiber diet is required.
• Improving response to antidepressants: Antidepressants are the main treatment for depression. Unfortunately, not everyone responds positively to the treatment. Research is being conducted now to understand if the microorganisms in the gut and the molecules they release affect the outcome of treatment using antidepressants. Preliminary research shows that patients with major depressive disorder who responded to antidepressants had a different composition of microorganisms than those who did not respond. The precise link of the microorganisms with the medication is not yet known, but in the future, it could help in developing better antidepressant treatments, potentially supplementing this with microorganisms for the gut.

Conclusion

Major depressive disorder affects millions of people worldwide. It is important to recognize that gut microorganisms interact with brain health in many ways and, hence, further research into the exact molecular mechanism and their nutritional impact is required. Based on the research, along with currently available treatments, modifying nutrition and the gut microorganisms of an individual could be used as a standard treatment method for patients with major depressive disorder in the future.