Gut Brain Axis: The Gut & the Brain - How Gut Bacteria Affects Mental Health
Everybody is talking about the #GutBrainAxis. It’s fair to say that the idea of the connection between the gut and the brain is not a new one. ‘Go with your gut feeling’ is an old saying that might have its roots in this notion. So are we simply re-discovering old concepts here? Science has recently been looking into the possibility of a ‘gut-brain connection’ with much greater focus. Over the past ten years the concept has really gathered some momentum with hundreds of studies now exploring the potential of this fascinating subject.
The US National Institute of Mental Health invested over US$1 million on a research programme focused on unlocking the secrets of how the microbiome is connected to the brain. The evidence from this initiative was presented in November 2015 at the meeting of the Society for Neuroscience in Washington DC called under the title: ‘Gut Microbes and the Brain: Paradigm Shift in Neuroscience’1.
The fire has been further fueled by the publication of Dr. Robert Perlmutter's book ‘Brain Maker’ in which he fully explores the gut brain connection. I’m halfway through this one and can confirm that it’s certainly a feast for the brain. Giula Enders also added to the wave of interest in her book, ‘Gut’, which included a chapter on ‘The Brain and the Gut’. Enders is a German writer and scientist who is currently studying for her PhD in gastroenterology at Goethe University in Frankfurt, Germany. She is another scientist who firmly believes that good mental and physical health begins in the gut, and that the gut-brain axis is key to our overall well-being.
The physical connection between gut and brain
Now let's look at how these two, apparently remote, areas of the body actually connect. In physical terms, the brain is connected to the digestive system by the vagus nerve, which is the longest of twelve different cranial nerves that link our intestinal nervous system to the central nervous system (CNS). This vital part of the neural network controls and co-ordinates a variety of key but ‘unconscious’ bodily functions from our heart rate to the digestive process.
Most view our digestive system as a reasonably simple pipe through which our food and drink passes, when in fact the intestinal tract has its own highly complex nervous system, known as the ‘enteric or intrinsic nervous system’, which is connected to the CNS via the vagus nerve. Because it is now being recognised that the intestines, like the brain, host such a multitude of neurons, some scientists are re-christening the gut ‘the second brain’, a worthy ‘spouse’ for its cerebral partner2.
Whilst it’s a little easier to see how the physical body parts are connected, it’s not so easy to see where our gut bacteria adds to this ‘romance’. Well, apparently, microbes in the gut can actually release chemical messengers that influence cell responses along the vagus nerve – acting just like our body cells – that then send communications via the vagus nerve to the brain (2,7). The gut bacteria provide the (bio)'chemistry' that binds this couple together!
How does the ‘gut-brain’ connection affect our mental health?
Whilst we are all quite aware of the obvious gut-brain connection, the ‘fight or flight’ response that makes us feel like running to the loo in stressful situations, scientists are now recognising that may be far broader implications for health. Neuroscientists are now looking at the role of the gut microbiota in the study of many mental disorders from Parkinson’s Disease to depression. Other studies have also shown great promise for the use of probiotics in the support of social anxiety and other generalised anxiety-related conditions.
Even more exciting is the potential to unlock the minds of autistic children, as increasing evidence is suggesting a role for probiotics in the management of Autism Spectrum Disorders (ASD). Studies indicate that altered gut microbiota and digestive issues are often seen in children with ASD, and can adversely affect their behaviour, and also that the gut-brain connection could have a significant role in the development of the condition3.
For our thoughts on how probiotics may be able to help support autistic adults and children, healthcare practitioners may be interested in: ‘Probiotics for autism’.
Depression in focus
Depression is by far one of the most common mental disorders in modern society, however and so this scientific epiphany is good news for the millions of people worldwide who suffer from this broad range of syndromes falling under the term ‘depressive disorders’.
This term can encompass specific conditions such as social anxiety and seasonal affective disorder, and is linked to other mental health disorders such as ‘OCD’ (obsessive compulsive disorder) and PTSD (post-traumatic stress disorder). Specific studies have now looked at the possibility of applying probiotic bacteria to help alleviate symptoms of depression;
A recent study published in the journal ‘Nutrition’ looked at the effects of probiotic supplementation on a group of subjects known to be suffering from Major Depressive Disorder. The forty participants, who were aged between 20 and 55 years old, were separated into two groups: one group was given a probiotic supplement containing three species of bacteria, Lactobacillus acidophilus (2 × 109 CFU/g), Lactobacillus casei (2 × 109 CFU/g), and Bifidobacterium bifidum (2 × 109 CFU/g), and the other group was given a placebo. Their diets were also assessed along with their exercise regimes.
After an eight week period, it was determined that the group given the probiotics saw significant and measurable improvements on their Beck Depression Inventory, insulin, homeostasis model and assessment of insulin resistance4.
‘Psychobiotics’ – the anti-depressants of the future?
Obsessed as we are with all things probiotic, we have also been following this potential use for benefical bacteria closely for some time. In May 2014, our Kathy reported on the potential of probiotics for those suffering from psychiatric illnesses. Read her fabulous blog: ‘Psychobiotics – just a fad? Or here to stay?' Joanna also looked at another recent clinical trial which received a huge amount of media attention earlier this year: it examined the effects of a specific strain of probiotic bacteria - Bifidobacterium longum 1714 – in helping to reduce the symptoms of chronic stress.
Read more about this study, which was conducted at the APC Microbiome Institute at the University College Cork, in her blog: ‘New study supports probiotics for daily stress’
Don’t forget diet
Of course, if our microbiome can affect our mood and brain health so significantly, then it follows that our diet can also significantly affect our mental health too, as the type of diet we can directly influence the type of flora – ‘good’ or ‘bad’ – that flourish in our intestines. Dr. Perlmutter, an esteemed neurologist who is the president of the Perlmutter Brain Foundation, believes that eating a diet rich in fermented foods that feed the right types of gut bacteria is the key to good brain health, and offers a comprehensive diet plan in his book, 'Brain Maker'.
Conversely, on the blog recently, we covered the impact of junk food on our microbiome – if you want to be shocked, read another of Kathy’s blogs which explains how an excess of so-called ‘fast foods’ can have a significant negative effect on our gut microflora – and our brain function! - ‘Junk food alters gut bacteria and makes us less intelligent’.
To help promote his own book, which was also published this year, Professor Tim Spector from King’s College London put the junk food theory to the test using his 23 year old son, also called Tim. Prior to the experiment, young Tim’s gut microflora contained over 3,500 different species of bacteria, but after ten days these populations had plummeted down to just 1,300 species. Wipe-out!
Read more about this experiment in my blog: Fast food harms gut bacteria
Does our unique microbiotia influence our personality?
In the future, could psychological profiling soon include a breakdown of our microbiota? We know that it can affect our diet – pathogenic bacteria make us crave sugary foods (reference) but a recent study indicated that gut bacteria significantly affected the mood of toddlers. The research was conducted at Ohio State University, and focused on the spectrum of bacteria extracted from the intestines of a group of child subjects between the age of 18 and 27 months.
The intention of the study was not the assessment of behavioural patterns – it was originally focused on the role of the gut bacteria in the development of future health issues such as obesity, asthma, allergies and bowel disease. Whilst looking for clues as to how the microbiome in these toddlers might influence their adult health, the researchers noted that the presence of certain types of bacteria, the diversity of species and the size of the bacterial populations noticeably affected the behaviour of the children 5,6.
Fascinating stuff, and yet more ‘brain-food’ for us to consider when thinking about how to positively affect our mood; it appears that the key to our overall state of our sense of well-being lies in ensuring that there is a healthy relationship between our gut and our brain.
A marriage made in heavenly health
We think this year is the year for the Gut / Brain axis, when the two are officially recognised as a couple and truly married together by science. This marriage could have one of the most profound future potentials for good mental health that science has uncovered in recent years. Let’s hope that the research into this union continues to be fruitful, and gives birth to yet more evidence supporting the ‘Gut-Brain Connection’.
For related articles on this fascinating subject, click on the following links:
1. Reardon, S.,(2015), Idea that intestinal bacteria affect mental health gains ground. Nature, 12 November 2014, http://www.nature.com/news/gut-brain-link-grabs-neuroscientists-1.16316
2. Perlmutter, R. (2015) ‘Brain Maker’: Hodder & Stoughton: London
3. Krajmalnik-Brown et al, (2015) , ‘Gut bacteria in children with autism spectrum disorders: challenges and promise of studying how a complex community influences a complex disease’, Microbial Ecology in Health and Disease, Vol 26 (2015).
4. Akkasheh et al, (2015) ‘Clinical and metabolic response to probiotic administration in patients with major depressive disorder: A randomized, double-blind, placebo-controlled trial’, Nutrition, September 25, 2015
5. Lisa M. Christian, et al (2015), Gut microbiome composition is associated with temperament during early childhood. Brain, Behavior, and Immunity, 2015; 45: 118 D
6. Ohio State University Center for Clinical and Translational Science. "Toddler temperament could be influenced by different types of gut bacteria." ScienceDaily. ScienceDaily, 27 May 2015. www.sciencedaily.com/releases/2015/05/150527091438.htm>.OI:10.1016/j.bbi.2014.10.018
7. William W.L. Hsiao, et al (2008), The Microbes of the Intestine: An Introduction to Their Metabolic and Signaling CapabilitiesEndocrinol Metab Clin North Am. 2008 Dec; 37(4): 857–871.doi: 10.1016/j.ecl.2008.08.006