The Microbiota-Gut-Brain Axis 

The Microbiota-Gut-Brain Axis 

The gut and brain are in constant communication with each other. It’s a bidirectional signalling highway composed of neurons, hormones, and immune cells, and is commonly known as the microbiome-gut-brain axis. These systems work together in the microbiota-gut-brain communication system. This system has shed a lot of light on the ways in which the gut influences the brain and vice versa, and how it relates to physiological balance or homeostasis.  

It is telling then the gut contains more neurons than the spinal cord! As well as around 70-80% of immune cells in the body. It is for this reason that most of the chatter between the two is coming from the gut toward to brain – the gut is the perfect informer, since the trillions of microbes living there can, directly and indirectly, influence brain function, and this means how we feel – our mood, as well as how we behave. 

The gut has its own nervous system, called the ‘enteric nervous system’ which is why it’s often referred to as our second brain. This second brain can act independently of the brain, but often works in collaboration with the brain; communicating through the VAGUS NERVE – the main communication pathway in the gut-brain axis. What is interesting to note is that 90% of nerve fibres between the brain and the vagus nerve are signals travelling from the gut to the brain! 

Through this axis, the microbiome has an influence on cognition, memory, learning, mood and even our behaviour. 

Transmitters and neurotoxic substances produced by certain types of bacteria can enter the brain through systemic circulation and affect central nerve function by triggering a process called neuroinflammation. 

LPS is one such neurotoxin.  

When bacterial cells die, they shed their outer membranes – these membrane fragments are called Lipopolysaccharides (LPS). Trillions of bacteria in the gut contain LPS, and they are the primary source of this toxin in chronic, low-grade inflammation. If the LPS are kept within the confines of the gut, they are mostly harmless, but in cases where there is damage to the gut barrier system (aka leaky gut) LPS causes big problems, triggering an immune response and contributing to inflammatory diseases, including neurodegenerative diseases like Alzheimer’s Disease. An inflamed brain decreases nerve conductance, which can lead to depression and reduced activity of the vagus nerve – forming a vicious cycle – since poor vagal activity results in poor overall gut function.  

It is thought that the gut can have an effect on mood through a number of other mechanisms, too.  

For example, the gut microbiota is thought to directly affect the levels of mood-regulating neurotransmitters, such as serotonin, and has also been shown to have an affect on the HPA axis, which is important in our body’s stress response.  

There is a lot of recent research that mental disorders can be treated by regulating the microbiota – including anxiety, which is prevalent at the moment – with the use of probiotics. 

Microbiota modulating probiotics can improve the signals being sent to the brain via the vagus nerve and positively impact the way we think and feel and behave. Probiotics (aka live bacteria) can reduce intestinal inflammation and lower stress hormones, as well as increase short-chain fatty acid (SCFA) production.  

SCFAs are mainly produced by the bacterial fermentation of dietary fibres. They help reduce intestinal inflammation, support gut barrier defences, and communicate with immune cells. Evidence is now suggesting that SCFAs may also play a role in depressive-like behaviours. One animal study found that some SCFAs were significantly decreased in depressed mice compared to controls, with some species being correlated with serotonin. 

Fish oils are also able to modulate the gut microbiome. Omega-3 supplementation increases microbial diversity and enhances the production of something called intestinal alkaline phosphatase (IAP), which helps detoxify LPS.  

If you have persisting gut symptoms despite eating a paleo-style diet (no processed foods, limited grains, no gluten, no dairy, no refined sugars and a reduction in overall sugar intake, including from fruit) but you are still experiencing a lot of gut issues (bloating, abdominal cramps, heartburn or reflux, diarrhoea, constipation), that could indicate a brain-gut axis problem. Maybe you have also started recognises that your memory isn’t as good as it used to be, you’re more anxious, you have a short attention span, or even cold hands and feet. In fact, cold hands and feet is a very common sign of a dysregulated microbiota-gut-brain axis, since it is an indication of reduced blood flow in the periphery, and since your brain is essentially a peripheral organ, it indirectly shows a reduction of blood flow to the brain. 

The two best ways to increase blood flow to the brain are exercise and acupuncture, so anyone with a MGB axis issue should definitely be trying acupuncture.  

Ultimately the key intervention strategies for repairing or optimising the communication between the gut and the brain involve doing a complete gut restoration program. This might include introducing prebiotics, probiotics, glycine-rich bone broths – basically addressing anything that is either compromising the gut barrier system and causing leaky gut – which subsequently causes a leaky brain. Re-establishing good microbial balance through nutrition will positively influence the ‘gut ecosystem report’ that is being sent from the gut to the brain on a minute-by-minute basis.   

Another crucial point of intervention involves incorporating stress management techniques – this can be anything from mindfulness meditation, breathing techniques to soothe the soul, yoga, tai chi, acupuncture – whatever works for you.  

If you have gut problems and mood issues?

The two things may very well be connected via the gut-brain axis. If you are interested in addressing the root cause of both, our team of experienced naturopaths, nutritionists, acupuncturists, and network chiropractic practitioners will be on hand to offer a complete range of natural medicine therapeutics to get you back to your optimal self again.