How Your Gut Talks To Your Brain – And Why It Matters

The secret to a healthier brain might just start in your gut. That’s because certain foods shape the balance of gut bacteria, which play a surprising role in brain function through the gut-brain axis. 

What is the Gut-brain axis? 

• A powerful 2-way communication between the emotional and cognitive centers of the brain, and the functions of the intestinal system, like digestion, the permeability of the intestines (leaky gut), immune activation and intestinal reflexes. 

• Think of this communication route as a superhighway, and this highway is the vagus nerve – the longest of the 13 cranial nerves. The signals that travel along this superhighway are initiated by neurotransmitters, hormones and immune cells. 

• Like your brain (Central Nervous System), your gut (Enteric Nervous System) contains nerve cells, which are found in the lining of your digestive tract.  

• Microbes in the gut have an influence on these nerve cells, so they play an important role in this connection between the gut and brain. 

This means that your gut affects your brain  

and your brain affects your gut.  

How does your gut affect your brain?  

Stress is a prime example:  

• Certain bacteria then activate the stress circuits from the gut to the brain via the vagus nerve, and the signal that goes from your gut to your brain influences how you react to stress. 

• Stress can also increase the permeability of your gut. A permeable (leaky) gut can dump inflammatory molecules and toxins into the blood... 

  • ↳️ systemic inflammation  

  • ↳️ damage the blood-brain barrier (making it leaky as well)   

  • ↳️ inflammation in the brain.  

• When the gut is leaky, it also gives bacteria an opportunity to move across the inner lining of the intestinal wall and directly access immune cells of the ENS. This is therefore a potential mechanism for the gut bacteria to influence the brain via the immune system in the presence of stress. 

Do neurodegenerative and other brain disorders start in the gut? 

New studies are also showing a link between gut bacteria and Obsessive Compulsive Disorder (OCD), suggesting that specific gut bacteria may be the cause. Some of the gut bacteria linked to OCD are also linked to depression. This is expanding our knowledge of how the gut and brain affect each other. 

Inflammation is another example of the strong effect of the gut on the brain: 

The microbiome controls neuroinflammation 

↳ Bad bacteria produce inflammatory compounds 

↳ Good bacteria produce neuroprotective molecules 

↳ Diet directly shapes brain health through microbial metabolism 

Signaling between gut bacteria and the immune cells in the brain may have an influence on the development of neurodegenerative/inflammatory disorders like Alzheimer's Disease. It's been reported that gut bacteria differed between Alzheimer's patients and healthy individuals. Animal studies are taking that link a step further by demonstrating how putting gut bacteria from mice with Alzheimer's can induce cognitive effects in the young and healthy host animals. Read more here.

A new study with mice posits a new theory of the development of Parkinson's Disease by showing a direct link between the presence of gut bacteria and the development of the disease. Misfolded alpha-synuclein protein clumps (Lewy bodies) in the brain are a hallmark of Parkinson's. The work suggests that these clumps may originate in the gut and spread to the brain. Studies in humans show that intestinal issues, particularly constipation, can precede the motor symptoms of Parkinson’s by many years.

How does your brain affect your gut? 

Again, stress is a great example: 

• The two-way communication of the gut-brain axis means that the brain can directly influence the gut microbiome, potentially impacting the balance of gut bacteria. 

• Different types of psychological stressors (both short and long term) can affect the total biomass of the gut microbiota. In fact, exposure to social stressor for only 2 hours can significantly change the types and proportions of bacteria. 

• Stress can worsen the symptoms of Inflammatory Bowel Syndrome (IBS) - which is now considered a disorder mediated by the interaction of gut microbes and the brain, via the gut-brain axis. People with IBS are more likely to develop depression and anxiety. One does not appear to cause the other however, but unfortunately the two often go together.  

Hormonal Regulation: The brain releases hormones that affect gut motility, secretion, and permeability, impacting digestion and nutrient absorption.  

Neurotransmitters in the brain like serotonin, dopamine, and norepinephrine, which are involved in mood, behavior, and other brain functions, can also affect the gut environment. For example, stress-related neurotransmitters can alter the gut's pH and mucus production, influencing the growth and survival of different bacteria. 

The gut and brain are in constant conversation, reminding us that the body isn’t a collection of separate systems—it’s a deeply interconnected ecosystem. When we care for one part, we support the whole.