Summary: There is mounting evidence that the gut-brain axis plays a broader role in health. It also appears to have much influence on the brain health. The gut has more neurons than the spinal cord, producing numerous hormones, neurohormones, and neuropeptides. The gut produces 95% of serotonin. Additionally, the vagal nerve that innervates the gut also has a greater number of ascending fibers. All this means that managing gut health or even influencing the production of neurohormones by the gut could manage various systemic diseases and brain disorders.
Keywords: gut, gut-brain axis, serotonin, gut-brain axis and depression, depression
The role of the gut in influencing food choices, metabolic disorders is all too obvious. However, new studies show that the role of the gut is not just limited to digestion. It seems to have a much greater say in decision-making, influencing various choices made by people. It also means that dysregulated gut may cause brain disorders.
The gut can differentiate between various food items. Its preference for sugars and fast-absorbing carbs may cause metabolic disorders like diabetes. However, it appears that the gut can send strong signals to the brain, thus influencing various lifestyle choices.
The gut-brain axis has a much broader role in human health than thought earlier. Experts are now calling the neural network of the gut a second brain1.
Most people know that the brain can influence various body functions. It does so by sending signals via nerve cells. Additionally, an autonomic nervous system independently controls various body tasks with minimal intervention by the brain.
Although the brain does not interfere much in the day-to-day activity of internal organs, if needed, it can control the functioning of organs by sending signals via the vagal nerve and hormonal messengers. But, to the surprise of researchers, it appears that the vagal nerve has a greater number of ascending fibers than descending fibers. This indicates a two-way communication between the gut and the brain and shows that perhaps the gut has greater influence over the brain2.
Further, the presence of more neurons in the gut than in the spinal cord also suggests that the gut can significantly influence the brain. This is because the gut does not need so many neurons just to maintain its motility. Instead, these neurons produce various neurohormones and neuropeptides.
It is now a well-known fact that one of the most vital neurohormones influencing mood, serotonin, is primarily produced in the gut. It is estimated that almost 95% of serotonin is made in the gut3.
Experts are now trying to understand the broader role of the gut in human health. Especially they would like to know how the gut influences brain health. It appears that the gut primarily uses serotonin to communicate with various brain centers. At the same time, the role of serotonin in mood and emotional disorders is quite well known.
Drugs used to treat depression may enhance serotonin and thus may cause osteoporosis. Therefore, it may be possible to manage this osteoporosis by suppressing serotonin production in the gut. Similarly, there is a need to explore the role of the gut in other systemic disorders.
This understanding of the role of the gut in brain health is already helping manage some conditions like irritable bowel syndrome and chemotherapy-associated nausea more effectively.
Researchers are already thinking about targeting serotonin molecules in the gut by using non-absorbable medications that bind to the gut lining. Such medications might help treat anxiety and depression without causing systemic side effects caused by traditional drug therapy.
However, there is still a need for developing a greater understanding of the role of the gut, particularly the role of serotonin, in maintaining communication between the gut and the brain
Thus, researchers recommend people,to consume a diet rich in dietary fiber to maintain optimal brain health. In addition, exercise regularly, quit smoking to prevent various metabolic disorders, lower cholesterol, and prevent brain disorders.
1. Avetisyan M, Schill EM, Heuckeroth RO. Building a second brain in the bowel. J Clin Invest. 2015;125(3):899-907. doi:10.1172/JCI76307
2. Bonaz B, Bazin T, Pellissier S. The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis. Frontiers in Neuroscience. 2018;12:49. doi:10.3389/fnins.2018.00049
3. El-Merahbi R, Löffler M, Mayer A, Sumara G. The roles of peripheral serotonin in metabolic homeostasis. FEBS Letters. 2015;589(15):1728-1734. doi:10.1016/j.febslet.2015.05.054