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Personal Health Q3 2021

Understanding the impact of the gut brain connection

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Dr Cara Dunne

Gastroenterology Consultant, St James’s Hospital and @CHI, IrSPEN Director, ISG member

We all know that we can feel tension and anxiety in the “pit of our stomach” but also happiness and excitement. Now there is the science out there to prove it too. 

The gut microbiome is made up of trillions of live microbes living in the human intestine. It contains at least 150 times more genes than the human genome. It is a complex ecosystem with amazing diversity. It consists of bacteria, viruses, fungi and yeasts. They live symbiotically with us, metabolising foods, processing vitamins, and supporting our immune system.

The gut-brain axis is a two way communication system between the brain and the enteric nervous system.

The gut-brain axis

The gut-brain axis is a two way communication system between the brain and the enteric nervous system (ENS). The ENS is an integrated circuit of 100 million neurons embedded in the lining of your gastrointestinal tract. It coordinates the digestive process devoid of input from the brain, earning it the name of the “second brain”. 

How the microbiome interacts with the ENS and the brain was proposed in the landmark study by Nobuyuki Sudo and colleagues. They discovered that germ-free mice, which are born without any bacteria, had an impaired stress response. Sudo then gave the germ free mice healthy gut microbes and showed that the mice developed a normal stress response. The experiment demonstrated how gut bacteria can affect behaviour.

Further research on the mechanism was proposed by John Cryan and Ted Dinan at University College Cork. They demonstrated a combination of ways the axis communicates including hormones, microbial metabolites, neurotransmitters and immunological factors. When these are released from the gut, they send signals to the brain. To describe bacteria which affects the brain and mood, the team coined the term psychobiotic. 

Ways to balance your microbiome

Eat fibre rich foods: Short-chain fatty acids (SCFA) are produced from microbial fermentation of fibre and appear to have an anti-inflammatory affect and are a source of energy for your colon cells. Eating fibre-rich foods, such as fruit and vegetables promotes their formation. 

Good news, wine and chocolate are good for you, in moderation: Dark chocolate i.e. 70% cocoa, red wine, coffee and tea all contain polyphenol which our microbiome metabolise into bioactive metabolites. These can help to control bodyweight by inhibiting appetite and improving lipid metabolism.

Eat fermented foods: A new study from researchers at Stanford School of Medicine demonstrated that eating foods such as yogurt, kefir, fermented vegetables and kombucha tea led to an increase in overall microbial diversity.

Therapies such as cognitive-behavioural therapy (CBT) involve relaxation techniques and cognitive restructuring, teaching people to challenge negative thoughts and manage stress better. 

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