The Gut-Brain Connection

February 25 09:37 2022 Print This Article

The English language has many interesting expressions around the gut. Some of them are “it was a gut feeling”, “it was a gut-wrenching experience”, “felt sick to the stomach”, “feeling nauseous”, “my gut was in my mouth” etc.

So also, in India, traditional wisdom around health and diet has some interesting practices. Some of them are – eating curds before leaving home for an important event, not eating anything fried or spicy on the day of an exam, eating almonds for better memory, avoiding consumption of meat on certain days, having a light dinner, eating curd rice at the end of every meal, etc.

All of the above expressions and practices endorse, or emphasize what scientists are appreciating better, in the last couple of decades – which is – the gut-brain connection! One of our earlier articles “7 signs of an unhealthy gut” explored how an unhealthy gut can affect psychological or cognitive health. In this article, we will explore the gut-brain connection a little more.

The gut-brain axis

The gut, which is a collective expression for the digestive tract (excluding the mouth), is rich in microorganisms that affect our health in different ways. There are over 500 species of microorganisms collectively called the microbiome and the individual species – microbiota.

So it’s now acknowledged that gastrointestinal conditions like constipation, distension (swollen abdomen), nausea, diarrhea, gas and bloated sensation can be influenced by psychological conditions like anxiety, depression and stress. The connection works the other way too. Poor gut health caused by poor eating habits can affect one’s mental health causing irritability, anxiety, anger issues and depression.

So one can easily conclude that there is a clear neurological channel between the gut and brain. Scientists have even given a name for this – the gut-brain axis.

How does the axis work?

Bio-chemically speaking, the gut-brain axis is comprised of and influenced by five different factors.

The Vagus Nerve and Enteric Nervous System

The central nervous system comprises the brain, spinal cord and a vast network of major and minor nerves that carry signals from and to the brain, and different parts of the body.

• One such major nerve is the Vagus nerve that connects the brain to the gut. The gut is lined with nearly 500 million neurons which are constantly receiving signals from the brain and transmitting signals to the brain.
• This layer of nerve cells acts as a ‘little brain’ which is constantly conversing with the central brain, and forms what is called an Enteric Nervous System. Stress, anxiety, anger, etc. affect the signals sent by the Vagus Nerve and cause gastrointestinal conditions. In some studies, people with conditions like Irritable Bowel Syndrome and Crohn’s disease have reduced function of the Vagus Nerve. Similar findings have emerged from lab studies done on rats.

Neurotransmitters

Neural pathways between the gut and brain are not the only channel of communication between the gut and brain. There are chemicals secreted by the brain or gut which establish a conversation and these chemicals are called neurotransmitters.

• The best example for this would be the feel-good hormone serotonin. Only 30% of this is produced by the brain while the remaining 70% is produced by the gut. These neurotransmitters control emotions, feelings and also gastrointestinal health.
• Another such neurotransmitter is gamma-amino-butyric-acid or GABA which controls feelings of anxiety and depression. Consuming the right kind of food can control the production of GABA and relieve symptoms of such feelings.

Chemicals produced by gut bacteria

Neurotransmitters are not the only chemicals produced by the body. The 500 species which amount to trillions of microbes also produce chemicals that affect the brain.

• They produce innumerable short-chain-fatty-acids such as acetate, propionate and butyrate. Butyrate and the microbes producing it form a blood-brain barrier which acts as a filter preventing harmful chemicals from reaching the brain and only allowing water, oxygen, carbon-di-oxide and anesthetics to pass into the brain. Propionate reduces appetite slightly, which in turn helps reduce food intake and stimulating that part of the brain which feels rewarded by high-energy food. This goes a long way in curbing binge-eating.
• Gut microbes also metabolize or break-down amino acids and bile acids which are known to affect the brain. Bile acids are produced by the liver and play a part in absorption of dietary fat. But the way gut bacteria metabolize them can affect fat absorption and hence weight.

Gut microbes and inflammation

The gut-brain axis has a direct connection to our immune system. Toxins and pathogens that get into our body from food, water and air are filtered by the immune system and the gut barrier. The immune system attacks pathogens and reduces the effect of toxins. The gut barrier prevents toxins from leaking into the blood from the gut. If the immune system is constantly stressed by harmful chemicals and toxins in the body, it can lead to inflammation which is a major trigger for many health conditions. Gut microbes improve immunity and reduce inflammation.

• Constant stimulation of the immune system can lead to inflammation and trigger conditions like depression and Alzheimer’s.
• Lipopolysaccharide (LPS) is a toxic chemical produced by some of the gut bacteria and this can cause inflammation. In a healthy person, the gut barrier prevents LPS from entering the blood. However, in some people, the barrier becomes leaky causing LPS to enter the blood. Both inflammation and LPS in blood are triggers for conditions like depression, schizophrenia, and dementia (a risk for Alzheimer’s).

Prebiotics and Probiotics

Since its established that gut bacteria can affect mental health, consuming certain bacteria through food can improve mental health or relieve the symptoms of certain conditions. That is why, such bacteria are called Psychobiotics and are of two major types.

• Prebiotics are plant fibers that are fermented by gut bacteria and affect mental health in the process. For example, a prebiotic called galacto-oligo-saccharide (GOS) is known to reduce levels of cortisol, the stress hormone in the body.
• Probiotics: These are present in the gut and can also be augmented through food. As we all know, Lactobacillus, the bacteria that converts milk to curd is good for our digestion. That is the best example of a probiotic. Another probiotic Bifidobacterium longum NCC3001 is prescribed to relieve symptoms of irritable bowel syndrome (IBS), depression and anxiety.

Incidentally, anti-biotics are medications or drugs that are targeted at a particular disease-causing strain of bacteria or virus. However, they also destroy some of the prebiotics and probiotics in our body, temporarily, which is why antibiotics are the last choice of medication for any condition.

How do I use this information?

If you repeatedly suffer from gastrointestinal or mental health issues, it’s time to consult a dietician or nutritionist at a reputed hospital. He/she will incorporate foods that are beneficial to your gut-brain axis, in your diet. This includes Omega-3 fats, fermented foods, high-fiber foods, tryptophan-rich foods and polyphenol-rich foods.

In addition to this, you may be interested to know that there are a whole lot of mind-body therapies aimed at improving the gut-brain connection, such as Cognitive Behaviour Therapy (CBT), medical hypnotherapy, anti-depressants, etc. This brings hope to millions of people worldwide, who routinely suffer from gastrointestinal or mental health issues.

Kauvery Hospital is globally known for its multidisciplinary services at all its Centers of Excellence, and for its comprehensive, Avant-Grade technology, especially in diagnostics and remedial care in heart diseases, transplantation, vascular and neurosciences medicine. Located in the heart of Trichy (Tennur, Royal Road and Alexandria Road (Cantonment), Chennai, Hosur, Salem, Tirunelveli and Bengaluru, the hospital also renders adult and pediatric trauma care.

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