Updated: Jan 18
We’ve thought for a very long time that there is a connection between our gut and our brain, and recent interest in this hypothesis is proving our ‘gut-feeling’ correct.
Evidence from research studies is showing that the gut microbiota does, in fact, influence the brain (1), with mounting evidence demonstrating that an imbalanced gut microbiome may affect brain function in adults, resulting in an impact on stress, anxiety, and depression, and vice versa (2).
It has been found that manipulation of the microbiota may positively influence both the gastrointestinal and neurological symptoms of IBS. Furthermore, it has been noted that the management of IBS should have a large focus on managing stress through various non-pharmacological approaches, which should include dietary modification, probiotics, exercise, hypnotherapy and cognitive behavioural therapy (CBT) (3).
It’s not only adults who are affected. There is a clear connection of children experiencing ‘sore tummies’ when they are unhappy, anxious or stressed.
According to a systematic review from 2015, published by PLoS ONE (4), of up to 19% of school-aged children suffering from chronic abdominal pain and other gastrointestinal symptoms, almost 90% had no identifiable diagnosed disease attached to their symptoms.
It was concluded that teaching young people to identify their triggers and implement coping techniques to help reduce their stress such as mindfulness practice, and daily exercise can also be really helpful.
What is the connection you might ask?
There are multiple routes of communication between the gut and the brain. The gut-brain axis involves crosstalk between the endocrine system, the immune system, and the autonomic nervous system, and more specifically the vagus nerve, short-chain fatty acids, and the amino acid, tryptophan.
The gut-brain axis is a bi-directional communication system between the enteric nervous system (the gastrointestinal tract) and the central nervous system. Serotonin, or 5-HT, otherwise known as our happy hormone, is a key neurotransmitter in this system.
While it is well-known that serotonin is a brain neurotransmitter, scientists estimate that up to 90% of serotonin is actually made in the digestive tract (5).
The production and metabolism of tryptophan, or 5-HTP, the precursor to serotonin, relies on microbial regulation within the gut and may contribute to stress-related psychiatric disorders if this system is challenged (6).
Tryptophan metabolism occurs in both the central nervous system (CNS) and the enteric nervous system (ENS). Ensuring adequate dietary sources of tryptophan (i.e. protein) is key to maintaining a balanced mood, as well as stable blood glucose levels.
The vagus nerve is the longest cranial nerve in the body and its’ main function is to activate the parasympathetic nervous system, or the ‘rest and digest’ system, which can be stimulated by practising stress management techniques, outlined below.
These techniques may be especially relevant for those people affected by Irritable Bowel Syndrome (IBS), as IBS is thought to be due to a dysregulated gut-brain axis.
The Bottom Line
If you struggle with IBS, experience digestive distress or anxiety and/or depression regularly, you might want to consider if you are providing your brain and your gut the nutrients and stimulus that they need to function well and flourish.
How to keep your gut (and your brain) healthy
Dietary protein should be included at every meal. Especially those foods high in tryptophan, such as nuts and seeds, chicken and turkey, lamb, beef, pork, fish and shellfish, eggs, cheese, and legumes.
Tryptophan is an essential amino acid and the precursor to serotonin and melatonin (our sleep hormone), which supports a stable mood and a good nights’ sleep.
Probiotics and Prebiotics
Increasing evidence is showing us that the diversity of our gut bacteria is not only essential for our gut health but also normal physiological function in other organs, especially our brain (7).
A healthy gut microbiota consists of bacteria, viruses, fungi, and protozoa. When there is an imbalance of good (beneficial) bacteria versus pathogenic (bad) bacteria, this results in what is called ‘dysbiosis’ of the gut.
Dysbiosis is an imbalance of bacteria that occurs when the good bacteria have been overtaken by the not so good, or opportunistic bacteria. This can easily occur during times of great stress, excessive alcohol consumption or medications such as antibiotics, as well as poor dietary factors. It is important to get the ecosystem back into balance as soon as possible, as dysbiosis of the gut may lead to other chronic health problems.
Stool testing of the microbiome can help to determine exactly which microbes have become imbalanced, and a protocol can be put in place to correct and maintain balance, and to restore a healthy ecosystem.
Probiotics are live microorganisms that have beneficial effects on the host when consumed, by restoring the gut flora. Specific species and strains are important for the management of IBS, and these include Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus reuteri, Lactobacillus plantarum, Bifidobacterium longus, Bifidobacterium infantis, and Bifidobacterium breve.
Prebiotics are found in foods such as whole grains, onions, garlic, legumes, nuts, fruit, and vegetables. They are food for the probiotic bacteria or beneficial microbes in the gut. Including prebiotics helps the microbiota to thrive, positively influencing our gut health, behaviour, and mood.
Supplementary sources of prebiotics include galacto-oligosachharides (GOS) , fructo-oligosachharides (FOS), partially hydrolysed guar gum (PHGG), and polyphenol-rich ingredients such as citrus bioflavonoids, blackcurrant, grapeseed, cocoa, pomegranate and green tea.
Relaxing activities such as walking in nature, yoga and meditation, have positive benefits to our health by regulating our cortisol levels and stimulating the vagus nerve, therefore activating the parasympathetic nervous system. When the parasympathetic nervous system is activated, our digestion works more effectively, we sleep better, and we are more able to deal with stressful situations calmly and confidently.
Studies show that meditation and mindfulness when practised regularly, improve wellbeing, and decrease symptoms of stress and anxiety (8). Even a few simple breathing exercises can very quickly calm us down when we are stressed, anxious, and overwhelmed. Spending as little as 10 minutes a day practicing meditation can have far reaching health benefits. Ensuring to eat a healthy well-balanced diet and exercising daily are also excellent strategies to help with the management of stress.
There have been over 50,000 published documents relating to the microbiome in the last 10 years, with almost 2,000 of those articles directly relating to the microbiome gut-brain axis (9). While there has been considerable progress in this field of study, questions still remain, and further research is warranted.
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McEwen, Bradley and Fenasse, Rose. Probiotics and depression: 'The link between the microbiome-gut-brain axis and digestive and mental health' [online]. Journal of the Australian Traditional-Medicine Society, Vol. 25, No. 3, Spring 2019: 127-132. Availability: <https://search.informit.com.au/documentSummary;dn=954218795454605;res=IELHEA> ISSN: 1326-3390. [cited 06 May 20].
Hasan Mohajeri, M. et al. (2018) ‘Relationship between the gut microbiome and brain function’, Nutrition Reviews. doi: 10.1093/nutrit/nuy009.
Qin, H. Y. et al. (2014) ‘Impact of psychological stress on irritable bowel syndrome’, World Journal of Gastroenterology. doi: 10.3748/wjg.v20.i39.14126.
Korterink, J. J. et al. (2015) ‘Epidemiology of pediatric functional abdominal pain disorders: A meta-analysis’, PLoS ONE. doi: 10.1371/journal.pone.0126982.
Gheorghe, C. E. et al. (2019) ‘Focus on the essentials: tryptophan metabolism and the microbiome-gut-brain axis’, Current Opinion in Pharmacology. doi: 10.1016/j.coph.2019.08.004.
Dinan, T. G. and Cryan, J. F. (2017) ‘The Microbiome-Gut-Brain Axis in Health and Disease’, Gastroenterology Clinics of North America. doi: 10.1016/j.gtc.2016.09.007.
Carmody, J. & Baer, R.A., 2008. 'Relationships between mindfulness practice and levels of mindfulness, medical and psychological symptoms and well-being in a mindfulness-based stress reduction program'. Journal of Behavioral Medicine.
Zyoud, S. H. et al. (2019) ‘Global research trends in microbiome-gut-brain axis during 2009-2018: A bibliometric and visualized study’, BMC Gastroenterology. doi: 10.1186/s12876-019-1076-z.