The 8 Effects of the Brain-Gut Connection (Gut-Brain Axis Part 2)

In my last post, we learned the basics about your gut, your microbiota, dysbiosis, and the how it all connects to your brain to have an effect on the rest of your body.  

Today, I’m going to go into more detail first about the mental effects and then about the physical effects of your gut.


  1. Gut-Brain Axis Part 1
  2. Gut-Brain Axis Part 2
  3. Gut-Brain Axis Part 3
  4. Gut-Brain Axis Advanced

4 Mental Effects of the Brain-Gut Connection


Mental Health

The different microorganisms in your gut like lactobacillus, candida, streptococcus, and bifidobacterium strains produce different neurotransmitters.  Neurotransmitters are important because they’re what allow your brain cells (or neurons) to communicate with one another.  As I mentioned in the last article, these affect both your actual brain and your ENS or Second Brain.

There have been many studies about the effects of microorganisms (or lack thereof) on feelings of depression, anxiety, and stress.  One study done on rats found that microbiota were required for feeling anxious.  Another found that people with depression had increased levels of certain bacteria compared to those without depression.

On the flip side, to solve some of these mental issues, studies have given different kinds of bacteria to rats and have successfully reduced their occurrence.


Neurogenesis is the name for the creation of new brain cells.  New brain cells are created throughout our entire lives—in fact, about 700 new neurons are created in the hippocampus (part of your brain responsible for memory) every day!

Studies have found that taking antibiotics can decrease neurogenesis which can limit your cognitive function. But, taking probiotics and exercising can increase neurogenesis and repair damage done by antibiotics.

Autism Spectrum Disorders

Modern life is very different from that of our ancestors: our environment has become more hygienic, our diet has changed, and antibiotics are more widely used.  As a result, we come in contact with fewer microorganisms.  At the same time, the incidence of autism spectrum disorders (ASDs) has increased.  In experiments, mice living in sterile, germ-free environments had more ASD-like symptoms such as antisocial behavior towards other mice. When microorganisms were introduced to these “autistic” mice, their behavior changed to more normal, sociable patterns.

The gut of people with ASDs often have permeability problems (also called leaky gut) and an unbalance in their microbiota.  Probiotics may help to rebalance that.

Parkinson's Disease

Parkinson's Disease is the second most common neurodegenerative disorder.  For people with Parkinson's, instead of having the normal, healthy 700 new neurons a day, their brain cells begin to die.  It most often affects older people.

Often, people with Parkinson's also suffer from gastrointestinal issues like constipation, weight lost, and acid reflux.  Furthermore, when studying the stool samples of people with Parkinson's, doctors have found that they have a significant lack of a bacteria called Prevotella.  Although treatments such as fecal matter transplant which introduce new microbes into a person’s gut may be a cure in the future, evidence is still inconclusive.

4 Physical Effects of the Brain-Gut Connection

Irritable Bowel Syndrome (IBS)

Irritable Bowel Syndrome is caused by a biopsychosocial etiology.  Let me break down those dense medical terms for you.  First, “etiology” is a way of saying “cause” or “reason” and most often refers to what causes diseases.  “Biopsychosocial” describes a theory that puts a disease’s reason as being biological (like your genetics), psychological (depending on your mood or behavior), and social (your culture, family, and socioeconomic background).  This model broadens the possible causes of disease from the formerly accepted “biomedical” model that only takes the biological causes into consideration.

As a result, IBS alters aspects of the brain-gut axis.  IBS lowers the number of short chain fatty acids (SCFAs) in the body. SCFAs are produced by microbes in the colon that the brain needs for metabolism.  IBS is correlated with psychological issues like depression and anxiety and some studies suggest that childhood trauma may be a factor in its development.

Disrupt Metabolism

SCFAs are important for other parts of your body, too.  They give you energy, make sure your skeleton stays strong, and maintain your metabolism.  Your metabolism is responsible for converting food into fuel and nutrients and eliminating waste and toxins.  As a result, negative changes to your microbiota can result in obesity and metabolic disorders by affecting your gut’s ability to properly carry out its job.

Immune System

As I discussed in my last article about PPIs, your digestive system is a vital part of your body’s defense against germs and disease.  The immune system also helps the body stay in homeostasis—or functioning normally.  If your normal gut flora is off balance, the rest of your body (including your immune system) can follow.

The microorganisms in your gut produce proteins called cytokines are that responsible for changing the behavior of cells.  Autoimmune disorders are caused when these signals tell your immune system cells the wrong thing causing them to act abnormally.  Some cytokines are known to cause depression when they travel to the brain through the bloodstream.

Increased Allergies

Allergies are also a type of autoimmune issue and like autism they are on the rise as a result of a more hygienic environment and increased use of antibiotics.  Studies have shown that increased exposure to a diversity of microbes at a young age can prime the body and the immune system to know which substances are harmless and shouldn’t trigger an allergic response.

TLDR: When there are issues with your internal flora, it hurts your mental and physical health.

In My Next Post


In my next post, I’ll share what I’ve learned both from my research and from personal experience to keep my gut and my brain healthy.  

For now, try some butyrate😉

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