The Link between Gut and Brain Health

February 21st, 2022

The bidirectional communication system between your gut and brain is called the gut-brain axis. These two organs are connected through the vagus nerve, neurotransmitters, production of short-chain fatty acids (SCFAs) by gut microbiota and the immune system. This gut-brain link works in both directions. Gut bacteria affect brain health and, therefore, altering your gut bacteria through compounds such as probiotics and prebiotics may improve your brain health.

The-link-between-gut-and-brain-health

The Gut-Brain Connection

Did you ever “go with the gut” to make a decision? Have you ever felt “butterflies in your stomach” when nervous? This is because the brain and the gastrointestinal system are closely connected.

The bidirectional communication system between your gut and brain is called the gut-brain axis. These two organs are connected both physically through the vagus nerve and biochemically through hormones and neurotransmitters.

Gut microbiota has an important impact on the gut-brain axis, interacting not only locally with intestinal cells and enteric nervous system (ENS), but also directly with the central nervous system (CNS).

The Vagus Nerve

Your gut contains 500 million neurons, connected to your brain through the nervous system [1].

One of the biggest nerves connecting your gut and brain is the vagus nerve, which sends signals both ways. Gut microbiota communication with the brain, therefore, involves the vagus nerve [2].

Conditions such as Chron’s disease and irritable bowel syndrome (IBS) involve brain-gut dysfunctions where the vagus nerve is an important component.

People suffering from these conditions actually have a reduced vagal tone, which indicates a decreased function of the vagus nerve [3].

Neurotransmitters

Your gut and brain are also connected through neurotransmitters. Neurotransmitters produced in the brain have an impact on our feelings and emotions.

Many of these neurotransmitters are produced by our gut cells and microbiota as well.

Around 90% of serotonin, a neurotransmitter that contributes to feelings of happiness, is produced by enterochromaffin cells, a group of gut mucosal cells [4].

Gamma-aminobutyric acid (GABA), a neurotransmitter that helps control feelings of fear and anxiety, is also produced by many species of Lactobacillus and Bifidobacterium in the gut microbiota [5].

Production of SCFAs by gut microbiota

Gut microbiota produces short-chain fatty acids (SCFAs), such as butyrate, propionate and acetate.

SCFAs can affect brain function in different ways. They are able to stimulate the sympathetic nervous system, mucosal serotonin release and influence the memory and learning process in the brain [6].

Immune system

Your gut and brain are also linked through the immune system. The microbiota provides essential signals for the development and function of the immune system.

The microbiota, its metabolites and components are not only necessary for immune homeostasis, but they also influence your susceptibility to many immune-mediated diseases and disorders [7].

If the gut barrier becomes leaky, bacteria and lipopolysaccharide (LPS) –an inflammatory toxin produced by some bacteria– can enter the blood, causing inflammation.

Inflammation and high LPS content in the blood are associated with brain disorders, such as depression and dementia [8].

The Role of Probiotics and Prebiotics in the Link between Gut and Brain

The gut-brain connection works in both directions. Gut bacteria affect brain health and, therefore, altering your gut bacteria may improve or worsen your brain health.

Probiotics are beneficial live bacteria. Psychobiotics are a class of probiotics that are able to produce and deliver neuroactive substances such as GABA and serotonin, which act on the brain-gut axis [9].

Studies have found that some psychobiotics have antidepressant or anxiolytic activity. These effects may be mediated via the vagus nerve, spinal cord, or neuroendocrine systems [10].

Prebiotics are compounds derived from non-digestible carbohydrates, mostly fibre. Prebiotics may also affect brain health by lowering cortisol levels, the stress hormone [11].

Beneficial Foods for the Gut-Brain Axis

Some foods can be beneficial for the gut-brain axis. These include the following:

• Probiotic foods. Probiotics can be found in fermented foods and drinks, such as yoghurt, kefir, tempeh or kombucha.

Prebiotic foods. Prebiotics can be found in high fibre foods, such as vegetables, fruits, nuts, seeds and whole-grain products.

• Omega-3 fats. Omega-3 fatty acids can improve microbiota diversity [12]. These fats can be found in fatty fish, such as salmon, mackerel, tuna, herring and sardines.

• Polyphenol-rich foods. Polyphenols are found in foods such as cocoa, citrus, green tea, olive leaf and coffee. These compounds, digested by gut bacteria, increase healthy bacteria strains and may improve cognition [13].

• Tryptophan-rich foods. The amino acid tryptophan is the precursor of serotonin. Tryptophan is found in milk, cheese, oats, turkey and chicken, among others.