There is an intricate interplay that takes place between the gastrointestinal system and the central nervous system. The bi-directional cross-talk between these two seemingly separate systems is often referred to as the “Gut-Brain Axis”.
What is the Gut-Brain Axis?
The gut-brain axis is a two-way communication pathway between the gut and the brain. Signals can be sent directly from the gut to the brain and vice versa. This communication pathway consists of the signals from the enteric nervous system (the trillions of nerve cells that line the gastrointestinal tract), the vagus nerve, and the microbiota populations that reside within the gut.
The gut-brain connection accounts for why we have gut feelings and can experience nervousness or anxiety in our stomach. Those ‘butterflies’ in our stomach and the urge to ‘follow your gut ‘ are examples of the gut-brain connection at work.
The Gut’s Own Nervous System
As an extension of our nerve network, the gut has its own operating system called the enteric nervous system. The brain depends on messages from this network, made up of the trillions of nerves lining every corner of the gut. Messages are carried from the gut back to the brain with the help of the vagus nerve.
What might come as a surprise is that the enteric nervous system is in no way an inferior part of the nervous system. The enteric nervous system is massive and actually has more neurons than the spine! It also carries a lion’s share of neurotransmitter production, including those that are essential to our moods, such as serotonin and dopamine.
The Vagus Nerve – The Connector
The vagus nerve is the longest cranial nerve of the body, spanning from the brain to the waist. It crosses into multiple organ systems including the mouth, throat, heart, lungs, liver, and importantly, the gut. The vagus nerve is the communication superhighway that carries messages from the enteric nervous system and microbiota back to the brain.
Dysfunction or damage of the vagus nerve can have widespread health effects, many of which impact the digestive system. A dysfunctional vagus nerve may result in symptoms such as; abdominal pain, bloating, reflux, problems with swallowing, appetite loss, nausea, vomiting, and unexplained weight loss.
The vagus nerve is a fascinating nerve. Not only does it keep the brain informed of what’s happening at an organ level, but it holds a massive responsibility in regulating the digestive system, inflammatory responses, and immune processes. Interestingly, the vagus nerve responds favourably to mind-body interventions such as deep breathing exercises, yoga, meditation, and singing.
How Microbiota Influence Brain Health
Gut microflora (good bacteria) plays a key role in conveying messages back to the brain and can have a direct and measurable influence on the way we think and feel.
The populations of bacteria that live in our digestive system influence bowel movements, food digestion, enzyme production, and the uptake of nutrients. This gut bacteria also influences the integrity of the gut lining which has implications for immunity and inflammation, which in turn can affect mood and behaviour. They also secrete metabolites that have direct effects on mood chemicals.
There’s an emerging area of health care exploring psychobiotic focussed diets and specific probiotic bacteria strains for their mood-enhancing benefits. Therapy of this nature has the potential to change the way psychological health is managed, by having a focus on gut health and the beneficial bacteria within to improve a person’s mood and response to stressful situations.
Gastrointestinal inflammation has been linked directly with neuroinflammation. Given the widespread nature of the enteric nerves throughout the gut, it’s no surprise that an inflamed gut can create a domino effect of inflammation through the central nervous system to the brain. Inflammatory gut disorders (such as IBS) often result in mood, energy, and sleep changes and conversely, people diagnosed with depression often have associated gut dysbiosis (bad gut bacterial populations).
The complex links between messages from the microbiota, the vagus nerve, the enteric nervous system, and the brain highlight just how important gut health is to overall cognitive well-being. The close connection between the gut and the brain lends credence to the statement that you are what you eat!
REFERENCES
- Breit S, et al. Vagus Nerve as Modulator of the Brain-Gut Axis in Psychiatric and Inflammatory Disorders. Front Psychiatry. 2018 Mar 13;9:44.
- Limbana T, et al. Gut Microbiome and Depression: How Microbes Affect the Way We Think. Cureus. 2020 Aug 23;12(8):e9966.
- Sarkar A, et al. Psychobiotics and the Manipulation of Bacteria-Gut-Brain Signals. Trends Neurosci. 2016 Nov;39(11):763-781.