Recent studies show that your brain affects your gut health and even your gut may also affect your brain health. The communication system between the brain and your gut is called the gut-brain axis. Going forward we can explore the most important gut-brain axis and also foods that are very beneficial to its health.
How Are the Gut and Brain Connected?
The gut-brain axis is a term for a communication network that connects your gut with the brain. These two organs are connected both physically and biochemically in various ways.1
The Nervous System and the Vagus Nerve
Neurons are the cells that are found in the central nervous system and brain that helps your body how to behave. Approximately there are 100 billion neurons in the human brain. The gut contains around 500 million neurons, which are connected to your brain through nerves in your nervous system. The vagus nerve falls under one of the biggest nerves which connect your gut and brain. It sends signals in both directions. For example, in animal studies, stress mainly inhibits the signals sent through the vagus nerve and also causes gastrointestinal issues.
Another study in humans found that people suffering from irritable bowel syndrome (IBS) or Crohn’s disease had reduced vagal tone, indicating a reduced function of the vagus nerve. From this we can conclude that the vagus nerve is important in the gut-brain axis and its role in stress.2
Neurotransmitters
Your gut and brain are also connected through chemicals which are called neurotransmitters. The neurotransmitters that are produced in the brain have control over feelings and emotions. An example of neurotransmitter serotonin majorly contributes to feelings of happiness and also helps to control your body clock. Many neurotransmitters are also produced by your gut cells and the trillions of living microbes there. In the gut a very large proportion of serotonin is produced. Gut microbes are also responsible for producing a neurotransmitter called gamma-amino butyric acid (GABA), which helps to control feelings of fear and anxiety. Studies in laboratory animals have also shown that certain probiotics can also increase the production of GABA and also reduces anxiety and depression like behavior.
Gut microbes also produce other chemicals that affect the brain
The trillions of microbes that live in our gut are also responsible to produce other chemicals that affect how your brain works. Our gut microbes also produce lots of short-chain fatty acids (SCFA) such as butyrate, acetate and propionate. All the SCFA are produced by digesting fibers and they also affect brain function in a number of ways, such as reducing appetite. A study found that consumption of propionate help to reduce food intake and also reduces the activity in the brain related to reward from high-energy food. Butyrate another SCFA and the other microbes that produce butyrate are also important for forming the barrier between the blood and brain, which is called the blood-brain barrier.3
Gut microbes also metabolize amino acids and bile acids to produce other chemicals that can affect the brain. Bile acids are chemicals that are produced by the liver that are normally involved in absorbing dietary fats. They can also affect the brain.
Two studies performed on mice found that stress and social disorders reduce the production of bile acids by the gut bacteria and are also responsible for altering the genes involved in their production.
Gut microbes affect inflammation
The gut-brain axis is solely connected through the immune system. Gut and gut microbes play a very important role in building up of immune system and inflammation by having control over what has been passed into the body and what is excreted. If your immune system is working for long, it leads to inflammation, it is associated with various brain disorders like depression and Alzheimer’s disease.4
Lipopolysaccharide (LPS) is an inflammatory toxin that is made by certain bacteria. It can also cause inflammation if too much of it passes through the gut into the blood. This may happen when the gut barrier becomes leaky, it also allows bacteria and LPS to cross over into the blood. High LPS and Inflammation in the blood have been associated with a number of brain disorders including severe depression, dementia, schizophrenia and other functional gastrointestinal disorders such as gastro esophageal reflux disease (GERD), IBS, diarrhea, gastro paresis, functional constipation and fecal Incontinence.
References:
- Mayer EA. Gut feelings: the emerging biology of gut–brain communication. Nature Reviews Neuroscience. 2011 Aug;12(8):453-66.
- Herculano-Houzel S. The human brain in numbers: a linearly scaled-up primate brain. Frontiers in human neuroscience. 2009:31
- Anguelova M, Benkelfat C, Turecki G. A systematic review of association studies investigating genes coding for serotonin receptors and the serotonin transporter: II. Suicidal behavior. Molecular psychiatry. 2003 Jul;8(7):646-53.
- Ma Q, Xing C, Long W, Wang HY, Liu Q, Wang RF. Impact of microbiota on central nervous system and neurological diseases: the gut-brain axis. Journal of neuroinflammation. 2019 Dec;16(1):1-4.
