Your gut and brain are physically connected by millions of nerves, most notably the vagus nerve. The gut and its microbes also control inflammation and create many different compounds that can affect brain health.
How the Gut-Brain Connection Works and the Role of Nutrition
Recent research shows that your brain affects your gut health, and your gut can even affect your brain health. The communication system between your gut and brain is called the gut-brain axis. So How Do the Gut and Brain Connect? The gut-brain axis is a term for the communication network that connects your gut and brain. These two organs are connected in a number of different ways, both physically and biochemically.
Vagus Nerve and Nervous System
Neurons are cells in your brain and central nervous system that tell your body how to behave. There are about 100 billion neurons in the human brain. Interestingly, your gut contains 500 million neurons that connect to your brain via nerves in your nervous system.
The vagus nerve is one of the largest nerves that connects your gut and brain. It sends signals in both directions. For example, in animal studies, stress blocks signals sent through the vagus nerve and also causes gastrointestinal issues. Similarly, a study in humans shows that people with irritable bowel syndrome (IBS) or Crohn’s disease have reduced vagal tone, which in turn has reduced vagus nerve function.
An interesting study in mice found that giving them probiotics reduced the amount of stress hormones in their blood. But when the vagus nerve was cut, the probiotics had no effect.
This indicates that the vagus nerve is important in the gut-brain axis and its role in stress.
Neurotransmitters
Your gut and brain are also linked to chemicals called neurotransmitters. Neurotransmitters produced in the brain control emotions and feelings. For example, the neurotransmitter serotonin contributes to feelings of happiness and also helps control your body clock. Interestingly, many of these neurotransmitters are also produced by your gut cells and the trillions of microbes that live there. Large amounts of serotonin are produced in the gut.
Your gut microbes also produce a neurotransmitter called gamma-aminobutyric acid (GABA), which helps control feelings of fear and anxiety. Studies in lab mice have shown that certain probiotics can increase GABA production and reduce anxiety and depression-like behaviors.
Gut Microbes Produce Other Chemicals That Affect the Brain
The trillions of microbes that live in your gut also produce other chemicals that affect how your brain works. Gut microbes also metabolize bile acids and amino acids to produce other chemicals that affect the brain. Bile acids are chemicals made by the liver that are normally involved in the absorption of dietary fats. However, they can also affect the brain.
Two studies in mice found that stress and social disorders reduced the production of bile acids by gut bacteria and changed the genes involved in their production.
Intestinal Microbes Affect Inflammation
Your gut-brain axis is also linked to the immune system. Gut and gut microbes play an important role in your immune system and inflammation by controlling what passes into the body and what is excreted. If your immune system stays on for too long, it can lead to inflammation associated with a number of brain disorders such as depression and Alzheimer’s disease.
Lipopolysaccharide (LPS) is an inflammatory toxin made by certain bacteria. If too much passes from the gut into the blood, it can cause inflammation. This can happen when the intestinal barrier leaks, allowing bacteria and LPS to pass into the blood. Inflammation and high LPS in the blood has been associated with a number of brain disorders, including severe depression, dementia, and schizophrenia.