What Is the Gut-Brain Axis?
16 Jan 2022
The gut-brain axis is typically described as the ongoing and rather complex two-way communication that occurs between our central nervous system (CNS) and our digestive tract (GI tract).
The NHS states that around 4 in 10 people experience at least one digestive symptom at any one time, and chronic gastrointestinal health conditions are on the rise.1
Yet, with that said, why do we find talking about our bowels such a taboo topic? We are here to create that safe space and help lift the lid on all things gut health.
The gut contains up to an incredible 600 million neurons (more than our spinal cord!) that send and receive signals from the CNS.2 These processes are controlled by our enteric nervous system (ENS) which is a series of sensory and motor neurons lining the GI tract.
The nerve connecting our brain to our gut is the vagus nerve; the largest found in our body.3
Why is Our Gut Referred to as Our Second Brain?
It’s commonly stated when we sense threat or excitement or general overwhelm that our stomachs may ‘knot’ up, we sense a pit in our stomach and sometimes even feel the heat rising in our bellies when we are angry.
"I have a gut feeling about this" is another common phrase suggesting that we knew long before it was scientifically backed, that our brains and guts are connected in more ways than we previously understood.
There is new evidence daily to suggest that our gut health may have a significant effect on our mood, energy levels, and even our temperament.
But how and why is that? How can what we eat affect our mental health? and why does the state of our microbiome impact this?
Read on to find out why!
How Does Our Microbiome Affect our Brain Health?
Many of our hormones and neurotransmitters are actually produced in our gut through a fermentation process, triggered by ingesting fiber-rich carbohydrates (short-chain fatty acids).
This fermentation process produces bacterial strains which are then used to create several incredibly vital proteins and compounds affecting our endocrine system, gut hormones, and neurotransmitters.
If we have an overproduction of bad bacteria, this will negatively impact these processes, which leads to a dysregulated production of many proteins that affect our mental health.4
Creates Our ‘feel-good’ Neurotransmitters
A whopping 90% of serotonin (our happy hormone) is produced in the gut through the fermentation of bacteria. This neurotransmitter is also responsible for gut motility and can impact peristalsis (how quickly food moves through our digestive tracts).
If our serotonin production is low, it may negatively affect our mood along with increasing constipation.5
Other major neurotransmitters like dopamine (our feel-good transmitter), glutamate (responsible for GABA production), norepinephrine, and nitric oxide (a powerful antioxidant) are produced in the gut.6
Brain-Derived Neurotrophic Factor (BDNF), a protein that regenerates nerve cells, has been shown to be exceptionally vital to the survival of neurons and brain circuits involved in regulating mood and alleviating depression and anxiety.7
BDNF has also been shown to reduce symptom severity including abdominal pain associated with IBS. A study even supported a potential link between BDNF and a reduction in the damage of nerve axons in the colonic mucosa of patients with IBS.8
Supports Cognitive Function & Immunity
Studies have shown that our gut-brain axis may regulate cognitive function and immunity.
Two dozen small brain proteins, named neuropeptides reside with the major cells of the immune system inside our gut. These neuropeptides help to reduce harmful microbial activity in the gut and help modulate our immune response.9
How Can Probiotics and Prebiotics Improve the Gut-Brain Axis?
As shown, bacteria are needed to create a number of proteins and neurotransmitters that are vital for affecting our mood. It is vital, therefore, to have beneficial bacteria to help provide the right ingredients for these processes to take place.
Probiotics help populate the gut with good bacteria whilst prebiotics help to feed beneficial bacteria. Opting for a probiotic with a prebiotic strain is certainly beneficial and will help provide a great breeding ground for a thriving microbiome.
A relatively recent study showed that an imbalance of good to bad bacteria in the gut has been shown when studying a group of clinically depressed patients.10
Evidence has shown that probiotics may help to lower inflammation in the body which in turn benefits our mental health.
A study showed that chronic inflammation was a key driver in depressed patients.11
Inflammatory cytokines are released during these processes, which have been shown to strongly affect the central nervous system of patients with chronic anxiety.12
What foods Help the Gut-brain Axis?
So what foods can you include in your daily diet to help support your gut-brain axis?
Foods Rich in Short-Chain Fatty Acids
A diet rich in prebiotic short-chain fatty acids such as whole grains, brown rice, beans, and lentils is needed to create those neuroproteins that are vital for brain (and gut) health.
Omega 3 fatty acids from walnuts and oily fish have been shown to promote good bacteria in the gut and improve cognitive function.13
Polyphenol-rich flavanols such as green tea, cacao, and olive oil have been shown to feed beneficial bacteria and have even been shown to potentially benefit cognitive function.14
Prebiotic-rich foods such as sauerkraut, kimchi, tempeh, and kefir all feed the beneficial bacteria in our gut and help to populate our guts with good bacteria.
1. Common digestive problems and how to treat them - NHS (www.nhs.uk)