Understanding The Gut-Brain Axis - How it Works

What we eat influences how we think, feel, and behave. The gut and brain are connected and affect each other. They constantly communicate to optimize mood, focus, energy, and overall health. This communication is called the gut-brain axis and has two main functions: receive information about internal conditions and send signals to the brain.

The Gut-brain axis refers to a bidirectional connection between the central nervous system (CNS) and enteric nervous system (ENS).  It involves crosstalk between the endocrine, immune system, and autonomic nervous system. 

The Gut-brain axis is considered the third most crucial axis in the human body after the blood-brain barrier and nervous-immune system.

This axis includes the brain, liver, stomach, pancreas, spleen, and other organs in the GI tract. 

This article explores how the gut-brain axis works and what manipulates the gut-brain axis to support optimal health including focus and mood. 

Gut and Brain Connection

The gut and brain are connected in a way that it is hard to understand one without understanding the other. Both the gut and brain are constantly communicating and influencing each other.

The gut and brain interact through several mechanisms, which include: secretion of hormones by the pancreas, The release of neurotransmitters in the vagus nerve (the longest cranial nerve), activation of certain enzymes in the digestive tract that act on the brain, and the release of neuropeptides in the gut. 

The interaction between these two systems is essential because it plays a role in almost every body function. The gastrointestinal system affects mood, sleep, memory, immune response and more. A deep understanding of how the gut and brain interact is essential to our health and well-being.

The Gut-Brain Axis: How It Works

How do the gut and brain work together? The answer may surprise you. You might think that food goes through your mouth, down your throat, into your stomach, where it's digested, and then moves into your intestines. This is not exactly how it works. 

The gut and brain communicate in two ways: through the vagus nerve, which runs from the brain to the stomach, and through neuropeptides (substances made by nerves that carry messages between the brain and the body). 

These two communication systems support regulating and influencing many of our most essential functions such as emotions, sleep, memory, immune response, appetite, digestion, metabolism and more. Let's take a closer look at how they work. 



Gut-Brain Communication Via the Vagus Nerve

The Vagus nerve plays a significant role in connecting the gut and brain. Among 100 billion neurons in the human brain and 500 million neurons in the gut, the vagus nerve is one of the longest cranial nerves. It’s responsible for regulating intestinal motility, secretion, and absorption of neurotransmitters, hormones, enzymes, and many other substances in the gut. It runs from the brainstem to the abdomen, entering at C3 (cervical nerve)  and exiting at T8 (Caval hiatus). The vagus nerve regulates our heart rate, respiratory rate, and gastrointestinal motility (movement). In the past, scientists thought that messages from the brain to the gut only traveled via the vagus nerve. This is because they could record electrical activity in a specific area of a rat's brain and then measure how fast it moved through its digestive tract. They found that messages were sent from the brain but not in the opposite direction.

Today, we know that messages travel both ways along the vagus nerve. The brain sends messages to the stomach and intestines via this nerve; however, signals are also sent from the gut to the brain. These two systems work together in the following ways:

1. The vagus nerve influences the stomach and intestines to relax, which helps food move through your digestive tract more quickly.  
2. When you're stressed, the vagus nerve can trigger a fight-or-flight response in your body (like increased heart rate and blood pressure).  
3. The vagus nerve controls how quickly you feel full, which can affect your appetite.   
4. The vagus nerve helps to regulate digestive enzymes that help break down food into smaller molecules that are easier for the body to absorb.
5. The vagus nerve controls the amount of water you drink.

 

 

The Neurotransmitters

Neurotransmitters are another connector that links the gut and brain. It’s a chemical that controls the emotions and feelings in the brain. When we eat, the food is broken down into smaller molecules and enters our body through the gut. These molecules are then absorbed by cells in the digestive tract, which releases their neurotransmitters to transmit signals from one nerve cell to another.

The different types of neurotransmitters have been identified as follows:

• Neurotransmitters are released by the gut, but their activity is controlled by nerve cells in the brain. These neurotransmitters are found in most organs and tissues of the body. They play a key role in many physiological processes, including appetite, digestion, heart rate, blood pressure, and blood clotting. Neurotransmitters also affect mood, memory, sexual function, and behaviour.
• The neurotransmitter serotonin is associated with the brain's control of emotion and feelings such as happiness or sadness. It can influence the production of proteins in the body that help regulate many functions.
• The neurotransmitter dopamine is associated with the brain's control of movement and motivation. It influences a person's ability to learn, plan for the future, and focus attention. Dopamine is released in the body as a result of eating or drinking certain foods or drugs that stimulate appetite or trigger a desire for movement.
• The neurotransmitter acetylcholine is associated with the brain's control of memory and learning. It helps to regulate the body's use of energy, muscle strength, and bone growth. Acetylcholine also helps regulate attention and mood.

Gut Microbes

100 trillion microbes living in the gut affect how the brain works. These microbes work to extract vitamins and nutrients from food. Microbes produce SCFA (short-chain fatty acids) like propionate butyrate and acetate by digesting fiber. This SCFA is found in high levels when people have healthy guts and it affects brain function in several ways including appetite, blood sugar control, and mental health changes.

SCFA's have been shown to:

• Increase the levels of serotonin in the brain. This is thought to help with appetite and may be involved in reducing depression. It also helps maintain a healthy gut by maintaining beneficial bacteria and suppressing harmful ones.
• Help break down food for absorption into the body and prevent obesity and reduce hunger by regulating the feeling of fullness.
• Regulate blood sugar levels in the brain, which is essential for controlling mood.
• Protect against overgrowth of harmful bacteria in the gut, which can cause inflammation and contribute to bowel disease.

Immune system

The immune system is another essential connector of the gut-brain axis. Gut bacteria communicate with the immune system and send signals to regulate its activities. Gut microbes make some different substances that influence our immune response, including:

• LPS (lipopolysaccharides) - It can induce sickness behavior in animals and humans by binding to receptors on cells of the immune system.
• PGE2 (prostaglandin E2) - It's an inflammatory molecule produced by gut bacteria that can act as a messenger to signal the immune system.
• TNF-alpha (tumour necrosis factor-alpha) - is essential for maintaining the integrity of the intestinal lining and the immune system.

Inflammation and all these substances are associated with many brain disorders, including motor skills, vocal skills, severe depression, anxiety, dementia and schizophrenia. 

 

Probiotics, Prebiotics, Antibiotic and the Gut-Brain Axis

Gut bacteria affect the gut and brain health, so optimizing them supports the gut-brain axis.  

 

Probiotics and prebiotics

Prebiotics are specific kinds of fibers that can feed the microbiome to generate a healthy outcome. These substances restore balance in the gut and help to improve brain health. They can be found in whole grains, seeds, nuts, fruits and vegetables. Alternatively, certain prebiotic supplements support the growth of beneficial bacteria in the gut that produce SCFA, which improves gut health and the brain's function.

• Prebiotics producing GABA improve brain function and memory.
• Prebiotics can treat diabetes patients with gut bacteria problems by improving glucose tolerance.

• Prebiotics Bifidobacterium longum help treat obesity, improve intestinal motility and protect skin cells from bacterial infection and damage,
• Probiotics improve fat distribution and adiposity (fat accumulation) in rats with obesity. 
• Probiotics improve symptoms of constipation. 

 

Antibiotics

 

Gut bacteria play an important role in the mental state. It influences the brain’s ability to repair nerve damage.  

 

Researchers have found evidence of this in mice with bacterial infections in their brains.  A  study showed that bacterial infections in mice could cause changes in the expression of genes involved in learning and memory. The right antibiotic treatment for that particular bacteria boosts the level of a neurotrophic factor in the hippocampus that helps in boosting memory and mood. 

 

An improved gut-brain axis in mice supports increased levels of neurotransmitters, lowered stress hormones, and improved sleep, which leads to enhanced brain function.

 

How to improve gut-brain axis 

Over the last few years, scientific research suggests diets rich with antiviral and antibacterial fiber and herbs with healthy gut flora can set off a biochemical cascade resulting in reduced brain inflammation.  Less brain inflammation supports greater focus, less age-related cognitive decline and memory loss, and improved brain health.

Step 1: Take prebiotics- good dietary fibers,

Consider that dietary fiber is more than just about stool regulation. Some prebiotics are also good at supporting the growth of good bacteria in the gut, such as fruits, vegetables and fungi (such as mushrooms). 

Step 2 – Prebiotics Support the Growth of Good Bacteria in the Gut

Prebiotics also support the colonization and growth of probiotics which are orally consumed to enhance the gut microbiome. This is an active area of current research. Probiotic strains can help support a healthy balance of good bacteria in the gut including supplements containing bacteria strains that can help improve the digestive system and immune system. Scientists are looking at the microbiome and analyzing individuals for the flora of bacteria present in their microbiome for optimal health when taking probiotics with and without prebiotics.  

Step 3 – Good Bacteria in the Gut produce many molecules which have profound effects.

This is a key step in the process. Many studies are now demonstrating that prebiotics and probiotics feed the bacteria in the gut, which then produce many molecules that profoundly affect the capacity of leukocytes and tissue cells to produce selected cytokine networks.

Leukocyte research is important as cytokines are mediators of intercellular communication that contribute to controlling the growth and activity of other immune system cells and blood cells that help the body's immune and inflammation responses, specifically throughout the gut-brain network.

Step 4 – Increased Immunity and Reduced Brain Inflammation Improves Brain Health and Mood

Research has shown that some foods can inhibit the production of bacteria and viruses in the gut as well as provide natural detoxification to damaging chemicals. Some of these herbs include:

• Omega-3 fats: Fish oil, flaxseed oil and hemp seed oil contain omega-3 fatty acids, which are anti-inflammatory, help good bacteria in the gut, and reduce brain inflammation.
• Fermented foods: foods like Yogurt, kefir, sauerkraut, and cheese contains healthy microbes like lactic acid bacteria that alter brain activity 
• High-fiber foods: Whole grains, nuts, seeds, fruits and vegetables are  prebiotic fibers that reduce the stress hormone in the humans body
• Polyphenol-rich foods: Cocoa, green tea, olive oil, and coffee contains polyphenols that increase gut bacteria and can improve cognition 
• Tryptophan-rich foods: This amino acid converted in neurotransmitter serotonin is high in tryptophan, including eggs, turkey, and cheese.
  
  

Eating a diet rich in fruits and vegetables, especially those high in antioxidants such as blueberries, blackberries, raspberries and strawberries, will support a healthy body.

As a result, an optimally performing microbiome supports brain health, (cognitive function, attention and focus, mood and memory).

Conclusion

The gut-brain axis, or gut-brain connection, is a pathway that connects the brain and the digestive system. Understanding this connection can help kids and adults live healthier lives. Nerves and neurons run between the gut and brain, and the nerves producing chemicals also affect the gut and brain.