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Our Gut - The Second Brain

From as early as the 1930’s, scientists were beginning to understand that the health of our digestive system could influence our mood.



At a very early stage in the development of the fetus, the brain and digestive system develop from the same lump of tissue. This lump of tissue divides and forms our central nervous system and our enteric nervous system (this is the nervous system of our gut). The stomach and intestines are so rich in nerves that the enteric nervous system is often referred to as the “second brain.” There are about 100 million nerve cells in the gut and it stretches to around 9 meters in length.


Digestion is a complicated business, so it requires a dedicated network of nerves to oversee the functioning. As well as controlling the mechanical mixing of food in the stomach and coordinating muscle contractions to move it through the gut, the enteric nervous system also maintains the biochemical environment within different sections of the gut, keeping them at the correct pH levels and chemical composition needed for digestive enzymes to do their job.


An important ‘wire,’ the vagus nerve, connects our central nervous system and our enteric nervous system. The vagus nerve uses 90% of its fibers to send information from the intestines to the brain.


Our ‘second brain’ also shares many features with the first; it is made up of various types of neurons, it has its own version of a blood-brain barrier to keep its physiological environment stable and it produces a wide range of hormones and neurotransmitters similar to those found in the brain. In fact, neurons in the gut are thought to generate as much dopamine as those in the head and about 95 per cent of the serotonin present in the body at any time is in the enteric nervous system.


The state of our intestinal lining and the balance of bacteria within our digestive system has a major role to play in the production of our neurotransmitters: the chemical transmitters that tell our brain whether we should be feeling happy, sad, agitated or calm.


When the balance of our gut bacteria (collectively referred to as the microbiome) is affected, this has a major affect on our mood and levels of stress and anxiety.


The nerves in our digestive system are constantly speaking to the central nervous system. If the gut is irritated for some reason – if you have eaten something that you’re intolerant to, if you have a bad diet, if there is an imbalance in your microbiome or you have an infection – this can create an inflammatory reaction and will make your overall mood irritated as well.

Studies show that people with digestive-based problems and disease such as coeliac disease, Chrohn’s disease and irritable bowel syndrome (IBS), are significantly more likely to suffer from anxiety, depression and mood disorders. A recent study showed that 94 per cent of people with mood disorders such as major depression and anxiety also suffer from IBS. Depression is often worsened by an inflammation of the gut and therefore the troubled mind and unstable gut feed into one another in a negative way. So the connection can travel both ways; a troubled gut can send signals to the mind just as a troubled mind can send signals to the gut.


As mentioned earlier, serotonin is primarily produced in our digestive system. Serotonin is best known as the “feel-good” molecule and it is involved in preventing depression as well as regulating sleep, appetite and body temperature. Having too much or too little serotonin in the gut can cause an imbalance and trigger emotional disturbances.


When your gut is upset, you feel upset. But stress can affect your digestive system just as much as it affects your mood. Stress can alter the microbiome, leaving us more vulnerable to bowel issues, inflammatory conditions and the mental effects of these changes. It can impair the secretion of digestive acids, slow down the motility of the gut, allow unfriendly bacteria to grow, reduce your friendly bacteria and exacerbate leaky gut. This is a recipe for an unhappy digestive system, which can then go on to send more messages to your brain: so the cycle continues.


Clearly, there is a strong link between digestive issues and mental/emotional issues. Treating digestive issues through optimal diet, avoidance of food allergies and enhancing the intestinal microbiome can open up doors to improved mood and mental clarity. By treating these digestive problems it is possible to help with conditions such as anxiety, depression, chronic fatigue syndrome, schizophrenia and autism. Probiotics are one of the best tools when it comes to treating the gut, but it is always a good idea to consult with your health practitioner first.

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