The Gut Microbiome Can Directly Affect Our Mental Health

Your gut feelings may be transcribed by microorganisms…

The gut microbiota is a diverse collection of bacteria, viruses, protozoa, archaea, and fungi that live in the human gastrointestinal tract and are essential for many physiological processes. These microorganisms communicate with the peripheral and central nervous systems through the microbiota-gut-brain axis. The exact mechanisms of this communication are still being studied but involve neural, endocrine, and immune pathways. These pathways are often found to be altered in psychiatric disorders.

The gut microbiota can be modified through prebiotics, probiotics, antibiotics, synbiotics, postbiotics, and fecal microbiota transplantation to potentially treat psychiatric disorders, as these approaches are believed to improve mental health through their microbiota-modifying properties.

The primary phylotypes in the gut are called Firmicutes and Bacteroidetes and most studies use Lactobacillus and Bifidobacteria species [though probiotic yeast strains such as Saccharomyces boulardii have also been used.

However, microbial communities are unique to each individual and have specific finger-print-like characteristics. Therefore, the commonly used terms a ‘healthy gut microbiome’ and ‘dysbiosis’ may not be specific or diagnostic.

Probiotics are thought to contribute to a balanced gut environment by suppressing pathogens and interacting with host microbiota.

Possible Mechanisms of Psychobiotics on the Gut-brain Axis

• Hypothalamic-pituitary-adrenal axis (HPA) modification
• Neurotransmitter synthesis (such as gamma aminobutyric acid, serotonin, dopamine, noradrenaline, melatonin, histamine and acetylcholine)
• Modulation of brain-derived neurotrophic factor (BDNF)
• Modulation of oxytocin
• Interaction with the 10th cranial nerve (nervus vagus)
• Postbiotics (such as short chain fatty acids)
• Preservation/improvement of the intestinal barrier function
• Training of the immune system, immunomodulation
• Suppression of pathogens
• Shaping of neural networks
  
  

Source: Mörkl, Sabrina et al. “Probiotics and the Microbiota-Gut-Brain Axis: Focus on Psychiatry.” Current nutrition reports vol. 9,3 (2020): 171-182. doi:10.1007/s13668-020-00313-5 This article is licensed under a Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/.

The evolving field of nutritional psychiatry should be integrated into clinical practice to treat and prevent psychiatric disorders as well as metabolic comorbidities

Although the therapeutic use of probiotics to support mental health is promising, there are a number of factors that must be considered:

• Randomized, controlled studies to date have been small and diverse
• Probiotics may not work the same for every individual
• Probiotic bacteria are subject to natural selection and may acquire unwanted traits
• Probiotic therapy should be combined with a diet rich in micro- and macronutrients that support the development of a favorable gut flora
• Colonization resistance after probiotic ingestion may occur and debate continues as to whether colonization by probiotics is stable or merely a transient event
• Animal- and plant-based diets cause dramatic shifts of the gut microbiota within days
• Certain dietary patterns, such as the Mediterranean diet, are rich in plant-based foods and fiber that promote the growth of beneficial bacteria

Reference

Mörkl, Sabrina et al. “Probiotics and the Microbiota-Gut-Brain Axis: Focus on Psychiatry.” Current nutrition reports vol. 9,3 (2020): 171-182. doi:10.1007/s13668-020-00313-5 T