Gut brain axis

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You might know the expression, “I feel it in my gut”. Well, it sounds more real than you think!  Your gut and your brain are connected. Whether the butterflies in the stomach when you fall in love or the gut-wrenching experience before an exam, the gut-brain axis is the reason behind it. So, let’s unravel this fascinating science behind the gut-brain axis.

What is the gut-brain axis?

About 100 million neurons are embedded in the walls of your intestines and are collectively known as the enteric nervous system(ENS). This second brain in your gut communicates with your big brain directly. An upset gut can send signals to the brain, just as a distressed brain can send signals to the gut.

This bidirectional communication network that links the enteric and central nervous systems is referred to as the “gut-brain axis”.

The term “microbiota–gut–brain axis” is also used interchangeably to describe the role of gut microbes in the interplay.

How are the Gut and Brain connected?

The vagus nerve

The vagus nerve is one of the largest nerves that runs from your brain to your colon, physically connecting them, and carries an extensive range of signals from the digestive system to the brain and vice versa. 

Preclinical trials showed that feeding the mice probiotics (friendly gut bacteria) reduced the levels of stress hormones. But when the researchers cut the vagus nerve, this effect was no longer seen, suggesting that the vagus nerve is an essential part of the gut-brain axis.


Your gut and brain also communicate through chemical messengers called neurotransmitters that control your feelings and emotions. Interestingly, your gut bacteria can produce the same neurotransmitters as your brain.

For example, gut microbes can produce more than 90% of serotonin in the body. Serotonin affects your mood and feelings of happiness and pleasure.

Many species of Lactobacillus and Bifidobacterium bacteria also produce gamma-aminobutyric acid (GABA), a neurotransmitter that helps control feelings of fear and anxiety.

Post-biotics or short-chain fatty acids (SCFAs)

Through the fermentation of indigestible dietary fibers (called prebiotics), the gut microbes produce short-chain fatty acids (SCFAs) including acetate, butyrate, lactate, and propionate. SCFAs are beneficial metabolites (also known as post-biotics) that can cross the blood-brain barrier and influence brain functions.

Immune signaling

Another way that the gut microbiota seems to connect to the brain is via immune signaling. Gut and gut microbes are key role players in your immune system and inflammation by regulating what is passed from the gut into the body.

If harmful substances or pathogens pass from the gut into the blood, they will switch on the immune system and prolonged immune activation will lead to the release of inflammatory mediators which can connect to the immune cells in the brain.

Why is the gut-brain axis important, and what does it do?

“The gut-brain connection brings up new ways to think about diseases.” 

In the past, the gut was overlooked in finding solutions for neurological diseases. But for now, researchers and clinicians who are studying neurological disorders are keeping their eyes on the patient’s gut. Similarly, the clinicians who are treating certain gastrointestinal disorders now have a reason to include cognitive approaches like cognitive behavioral therapy in their recommendations.

#The gut-brain axis and anxiety

Studies have found that people with anxiety have different microbiomes compared to those without. They have more harmful gut bacteria that produce inflammatory chemicals linked to anxiety symptoms.

#The gut-brain axis and depression

In the past years, many studies have shown that gut microbiota dysbiosis influences brain functions and plays a vital role in the pathogenesis of depression. Although fewer studies are conducted in humans, the evidence so far suggests that gut microbiota modulation could become a new therapeutic target for depression.

#The gut-brain axis and neurodegenerative disorders

There is increasing evidence that the gut microbiota contributes to the pathogenesis of neurodegenerative disorders like Alzheimer’s and Parkinson’s disease. Alterations in the gut microbiota composition induce increased permeability of the gut wall and immune activation leading to widespread inflammation, which in turn may impair the blood-brain barrier and promote neuroinflammation, neural injury, and ultimately neurodegeneration.

#The gut-brain axis and functional gastrointestinal disorders 

IBS is a chronic functional GI disorder that is likely caused by intestinal dysmotility, abnormal immune activation, and changes in the composition of gut bacteria and the gut mucosal barrier. However, recent studies proposed that gut dysbiosis contributes to IBS symptoms via the induction of abnormal gut-brain connections. As a result, relaxation therapies have been shown quite effective as interventions to decrease IBS symptoms.

The rise of psychobiotics

A new understanding of the gut equals new therapeutic options. According to research, certain gut bacteria can potentially benefit mental health and cognitive function by 

  1. restoring normal microbial balance
  2. stimulating the vagus nerve
  3. producing neurotransmitters and SCFAs
  4. reducing inflammation

Researchers term these probiotic bacteria “psychobiotic”.

In one systematic review of clinical trials, psychobiotics have been shown to improve mental health and psychological function in people with depression, anxiety disorders, and Alzheimer’s.

How to support the gut-brain axis

Foster a healthy gut microbiome with probiotics

The gut microbiome plays an essential part in gut-brain communication. Therefore, it is vital to maintain a healthy gut microbiome. Probiotics are good bacteria that can beat their villainous counterparts and promote a natural balance in gut flora. You can get healthy probiotics from fermented foods and drinks like yogurt, kefir, kombucha, and sauerkraut or probiotic supplements.

Feed your microbes with prebiotic fibers

The gut microbes do a lot of beneficial work to clean your gut and expand your mind. So to keep them thriving, you need to feed them well. Vegetables, beans, and whole grains all have good amounts of fiber in them and can help to feed the friendly bacteria in your gut, acting as prebiotics.

Lifestyle changes

Eating a gut-friendly diet, minimizing stress levels, and being physically active are all important parts of improving your gut health which in turn will keep your brain healthier. For more detail, you can read here: How to improve gut health.

Change your gut to change your brain 

Though not all diseases begin in your gut, as Hippocrates said, your gut could likely be the culprit behind your neurological symptoms. Therefore, you can never go wrong with having a sound gut as it can pave the way to a sound mind.

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Dr Tun Min is s GP working in NHS UK and writing articles about supplements and vitamins based on personal clinical experience and clinical research.

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