Despite around 200,000 years of evolution, there’s still a lot we don’t know about the human body. As far as organs and systems interacting, we understand that it happens, but scientists are still learning what mechanisms are at play and why they work the way they do. Times are changing, though. Piece by piece we are gaining a better understanding of how the body works and how all the puzzle pieces fit together. One of the most exciting avenues of exploration is the link between gut health and mental wellbeing.
What is the connection between the gut and the brain?
It’s easy to assume that as two distinct parts of the body, the gut and brain might function in isolation of each other. However, the brain and gut send signals and information to each other in a mechanism known as the ‘gut-brain axis’1, which could be why the gut is often closely linked to our mood, stress and anxiety. For example, the gut can release hormones into the blood that tells the brain when we’ve had too much food, or not enough.
The digestive tract is lined with millions of nerve cells known as the enteric nervous system, or ENS. This system is sometimes referred to as a ‘second brain’, and while it isn’t capable of independent thought, it’s responsible for several important processes that we take for granted. The ENS helps2 to modulate digestion, release enzymes that speed up the breakdown of food, and supports nutrient absorption3 from what we eat. This is where gut bacteria come into play. The gut microbiome is an eco-system comprised of trillions of bacteria and other microorganisms, many different kinds, some of which can be particularly beneficial to the host. The development of the human microbiome in infancy is believed to help shape and refine the ENS4 in postnatal weeks.
The vagus nerve
For a long time, it was believed that the gut-brain axis was exclusively responsible for the release of hormones into the blood. However, a 2018 study5 by Hoffman & Lumpkin demonstrated a neural pathway that could emit and receive signals immediately. The research built on an earlier 2010 study that found that enteroendocrine cells, which line the gut and release certain hormones, resemble synapses that neurons use to send and receive signals. It was found that these cells could use electrical signals to ‘talk’ directly to the brain through the vagus nerve, the same way that neurons do. Until this study, it was believed that enteroendocrine cells ‘talked’ exclusively through the release of hormones, which we now know isn’t accurate. There are many advantages to this express connection between the gut and the brain, such as sensing harmful chemicals or pathogens and letting the brain know it needs a helping hand. A further 2018 study6 showed a link between the communication through the vagus nerve and the release of striatal dopamine, a de-stressing chemical, in the brain.
Can the gut and brain influence each other?
Although the relationship is bi-directional, almost 90% of the neural communication between the gut and the brain starts in the gut. This indicates that the gut, and its condition, could have a powerful influence on brain function, cognition and mental health. Although we are just beginning to understand more about the significant role of the gut-brain axis and its wider influence on overall wellness, there is clear evidence of the influence of mood and stress on the gut microbiome, and equally the gut microbiome influence on stress modulation7. The condition of the gut and how we’re feeding our gut microbiome can influence how we cope with stress levels. In the future, this could point towards the possibility of managing or alleviating stress and anxiety with changes to the diet.
- Carabotti M, Scirocco A, Maselli MA, Severi C. The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Ann Gastroenterol. 2015;28(2):203-209.
- Relationships Among the Brain, the Digestive System, and Eating Behavior: Workshop Summary.
- Guandalini, Stefano Enteric Nervous System: Intestinal Absorption and Secretion, Journal of Pediatric Gastroenterology & Nutrition: Volume 25 - Issue - p 5,6.
- Mueller NT, Bakacs E, Combellick J, Grigoryan Z, Dominguez-Bello MG. The infant microbiome development: mom matters. Trends Mol Med. 2015;21(2):109-117.
- A gut feeling
- A Neural Circuit for Gut-Induced Reward
- Schmidt K, Cowen PJ, Harmer CJ, Tzortzis G, Errington S, Burnet PW. Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers. Psychopharmacology (Berl). 2015;232(10):1793-1801.
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