Do gut feelings really exist?

–

Akanksha Mahajan

Final year MBBS

GMC Amritsar

Astonishingly, “gut feeling” or “butterflies in the stomach” weren’t mere expressions. Studies suggest that the gut and brain definitely influence each other’s overall functioning. So, the gut-brain axis involves various direct and indirect pathways between the cognitive, and emotional centres of the brain with the peripheral functions. Recent studies have brought up another interesting concept regarding how the gut microbiome can influence the structure, and functioning of the GUT-BRAIN AXIS.(1)

There are approximately 10¹⁴ microbes in the gut, which is 10 folds more than the cells in the human body. Disruption to the gut microbiota has been known to cause allergies, auto-immune conditions, and neuropsychiatric illnesses.

Studies suggest that the gut microbiome is responsible for the production of the various neurotransmitters which play a role in health and disease.

The gut-brain axis can involve the following major pathways:

• Vagus nerve: It is one of the largest nerves connecting the gut and brain

• Gut hormone signalling: The bacterial products influence the enteroendocrine cells to produce several neuropeptides that influence the enteric nervous system.

• Neurotransmitters: Gut microbes are also responsible for producing various neurotransmitters, such as gamma-aminobutyric acid (GABA), serotonin, etc., responsible for controlling various emotions and overall brain function.

Since gut microbes are directly involved in the production of neurotransmitters, therefore, disruption of the gut microbiota can have an adverse impact on the mental health of an individual.

Dysbiosis caused by a leaky gut has been found to be strongly associated with chronic neuroinflammation, which is the major cause of mental illnesses. (2) This inflammatory response can further induce cytokine production. These cytokines are further involved in the pathophysiology of mental disorders such as depression and anxiety disorders as they influence neurotransmitter synthesis, release, and reuptake. On the other hand, it has also been well-established how the response of CNS to various stressors can lead to dysbiosis by causing conditions such as irritable bowel disease, ulcerative colitis, etc.

Thus, the gut microbiome can be undoubtedly manipulated for the maintenance of appropriate mental health and the prevention of various neuropsychiatric diseases as well.

• Probiotics:

Various studies have suggested the role of probiotics in attenuating various neuropsychiatric symptoms. For instance- the role of lactobacillus rhamnosus in GABA expression has been found to be effective for the management of the major depressive disorder.(3)

• Antibiotics: Antibiotics have been found to have an adverse effect on the commensal bacteria in the gut. Research suggests that mice treated with antibiotics performed worse on memory tests as a result of the impaired hippocampal function. (4)

• Diet: Dietary habits are the most integral factor responsible for influencing the gut microbiota. Studies found that a gluten-free diet improved schizophrenia symptoms. However, more studies are needed to further prove the association between the two. (5)

And that’s not the end of it my friends, do you know that your gut microbiome can even influence your cravings for different foods? A new study by University of Pittsburgh researchers suggests that intestinal microbes may trigger foraging behaviours for foods containing certain nutrients. In the study, researchers saw that mice bred to have no microbiome but later colonised with the gut microbiomes of different animals showed significant variations in their dietary behaviours. The authors believe that gut bacteria could affect our food choices and cravings by influencing the availability of essential amino acids. (6) Tryptophan, an essential amino acid, is a precursor to the neurotransmitter serotonin. Scientists believe that this hormone may regulate diet selection.

Drs. Trevelline and Kohl discovered how the mice with different microbiota also had varying levels of tryptophan in their bloodstream before choosing different diets. The mice with more tryptophan also had more microbes that could produce the amino acid in their guts.

Tryptophan is one of the major chemical messengers that can communicate with the gut and brain. This experiment uncovers how tryptophan might directly affect day-to-day food behaviour.

The gut microbiome function and its influence on the gut-brain axis is quite fascinating, isn’t it? Doesn’t it trigger your curiosity to think of what might come next with the research still going on and on? Although, we still need more conclusive evidence regarding the extent to which the gut microbiome affects the GBA, however, one cannot deny the importance of healthy eating practices to ensure a healthy mind and a healthy body.

Bibliography:

1. Venter C, Eyerich S, Sarin T, Klatt KC. nutrients Nutrition and the Immune System: A Complicated Tango. 2020; Available from: www.mdpi.com/journal/nutrients
2.  Mörkl S, Lackner S, Meinitzer A, Mangge H, Lehofer M, Halwachs B, Gorkiewicz G, Kashofer K, Painold A, Holl A: Gut microbiota, dietary intakes and intestinal permeability reflected by serum zonulin in women. Eur J Nutr 2018, Epub ahead of print.
3.  Bravo JA, Forsythe P, Chew M V., Escaravage E, Savignac HM, Dinan TG, et al. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci U S A. 2011;108(38).
4. Möhle L, Mattei D, Heimesaat MM, Bereswill S, Fischer A, Alutis M, et al. Ly6Chi Monocytes Provide a Link between Antibiotic-Induced Changes in Gut Microbiota and Adult Hippocampal Neurogenesis. Cell Rep. 2016;15(9).
5. Eaton WW, Chen L-Y, Dohan FC, Kelly DL, Cascella N. Improvement in Psychotic Symptoms After a Gluten-Free Diet in a Boy With Complex Autoimmune Illness CASE PRESENTATION.
6. Trevelline BK, Kohl KD. The gut microbiome influences host diet selection behavior. Proc Natl Acad Sci U S A. 2022 Apr 26;119(17):e2117537119. doi: 10.1073/pnas.2117537119. Epub 2022 Apr 19. PMID: 35439064; PMCID: PMC9169907.