The Brain-Gut Connection

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If you have ever had “a gut feeling” to make a decision, or had “butterflies in your stomach” when nervous, it is likely that you are getting signals from an unexpected source: your second brain. In your digestive system, there is a “brain in your gut” and it  revolutionising medical and scientific understanding of the links between digestion, mood, health and even thoughts.

Scientists call this little brain the enteric nervous system but it’s not so little. The enteric nervous system has more than 100 million nerve cells lining your gastrointestinal tract from the oesophagus to the rectum.


Unlike the central brain in your head, the enteric nervous system (ENS), cannot do calculations or help compile a poem. The main role is controlling digestion, from swallowing to the release of enzymes that break down food to the control of blood flow that helps with nutrient absorption to elimination. The enteric nervous system appears to be not capable of ‘normal’ thought as we know it, but it communicates  with our central brain, with some insightful results.

The ENS may trigger big emotional shifts experienced by people coping with gastro-intestinal problems such as irritable bowel syndrome (IBS) and bowel problems such as constipation and diarrhoea, bloating, pain and stomach upset. Researchers and doctors have long believed that anxiety and depression contributed to these problems, but several studies have shown that it can also work the other way around. Researchers are finding more evidence that irritation in the gastrointestinal system may send signals to the central nervous system (CNS) that trigger mood changes.

This may explain why a high percentage of people with IBS and bowel problems also develop depression and anxiety, and because up to 30 to 40 percent of the population have bowel problems at some point in time, this is a significant finding.


This new understanding of the ENS-CNS connection helps explain the effectiveness of IBS and bowel-disorder treatments such as anti-depressants and mind-body therapies like cognitive behavioural therapy (CBT) and medical hypnotherapy. With the two brains communicating with each other, therapies that can help one may also help the other. Gastroenterologists ( medical specialists in digestive conditions) can be like counsellors looking for ways to soothe this second brain because, for example, they may prescribe certain antidepressants for IBS. This is because these medications calm symptoms in some cases by acting on nerve cells in the gut, and not because of any mental issues. Psychological interventions like CBT may also help to improve communications between the central brain and the gut brain.


We all know that a healthy diet is important for physical well-being. Scientists have now accumulated evidence about the pivotal role played by digestive microbiota in the cross-talk between the central brain and the gut. Technological advances have revealed the key role of the digestive microbiota in our main physiological functions (digestion, immunity, endocrine system, nervous system etc.)

Researchers have also been studying whether probiotics (live bacteria that are safe to eat) can improve gastrointestinal health and your mood. Thanks to their interactions with the brain-gut axis, probiotics have stimulated high hopes for brain-related health.

The idea that a dietary intake of live beneficial bacteria could help treat a mood disorder was first published as early as 1910, but it took over another half-a-century before indications that the microbiota was involved in the brain-gut dialogue. Since then many studies have demonstrated the impact of probiotic supplements in prevention of stress-induced intestinal abnormalities, improvement in gut permeability, normalisation of stress hormone, improvement in cognitive function and memory, reduction of depression and anxiety, promotion of a healthy mood balance, improvement in sleep quality.

Could probiotics be the medicine of the future for brain health? New and ongoing studies indicate that there are some potential applications for the years to come in certain areas where microbiota seem to play a key role: depression, autism, schizophrenia and Alzheimer’s to name a few. So, although not a magic bullet, probiotics could represent an additional tool to help address mood and psychological disorder through their interaction with the microbiota-gut-brain axis.