BiotiQuest® Gut Health & Probiotics Blog with Martha Carlin

Happiness From Belly to Brain: The Gut-Brain Axis

Martha Carlin | Jun 20, 2023 | 3 minutes read

The old adage of "you are what you eat" holds more truth than ever imagined as emerging research continues to shed light on the profound connection between our gut and brain. Imagine the trillions of little microbes in your belly weighing in on your breakfast choices or how you felt that day. It’s a fascinating thought, isn’t it?

Spanning beyond just digestion and metabolism, the microbiota in our gut is now believed to play a crucial role in shaping our emotions, behavior, and cognitive function. 

In this article, we explore the latest scientific discoveries on the gut-brain axis and its potential to transform the way we approach mental health and neurological disorders. Get ready to discover how your gut may hold the key to unlocking optimal brain health.

Microbes in the gut - do you need them?
You house a diverse population of microbes in your gut and other parts of your body such as the skin, mouth, ear canal, and more. Your gut microbiome has the most abundant population of microbes including bacteria, fungi, and viruses which share symbiotic relationships that benefit the microbial population and the host.

With over 3.3 million unique genes in the human gut – 150 times more genes than the human genome itself – the human gut microbiome is capable of synthesizing a mix of metabolites that the human body can’t. Species both potentially helpful as well as harmful that depend on and benefit each other by exchanging various bioactive compounds and metabolites such as short chain fatty acids (SCFAs), bacteriocins (control pathogenic bacterial populations), neurotransmitters and amino acids form this forgotten organ.

The gut microbiome plays a crucial role in directing and influencing critical processes such as the digestion of complex carbohydrates and absorption of nutrients, intestinal permeability, immune health, and synthesis of various amino acids, vitamins, and enzymes that are necessary for optimal physical and mental health. Microbially-derived neurotransmitters and precursors to neurotransmitters such as glutamate, GABA, serotonin, and dopamine, SCFAs (short chain fatty acids), as well as BDNF (brain-derived neurotrophic factor), are essential for stress and anxiety management, learning, memory, antioxidant, and anti-inflammatory activity. 

The gut-brain axis or the gut microbiome brain connection
Your intestinal microbiome and brain interact with each other across multiple channels such as neural (vagus nerve), hormonal (hypothalamic-pituitary-adrenal axis or HPA axis), and metabolic pathways. 

This bidirectional communication system is known as the gut-brain axis (GBA). The GBA forms a connection between the central nervous system (CNS), the enteric nervous system (ENS), and the gut microbiota. ENS is the part of the nervous system that regulates the gastrointestinal tract and its functions. Essentially, the gut-brain axis connects the emotional and cognitive centers of your brain with the body’s digestive functions.

Happy microbes lead to a happy brain
The crosstalk between the gut and brain ensures optimal gut health and has an effect on motivation and cognitive function as well as the early development and maturation of both ENS and CNS. 

Research has found increasing associations between dysbiosis (an imbalance in the gut microbiome) with CNS (neurological) and functional gastrointestinal disorders (FGIDs) such as Alzheimer’s, Parkinson’s, and IBS, which are further associated with mood disorders such as depression and anxiety. The absence of the microbiome at developmental stages has been associated with having a negative impact on crucial processes such as altered levels of neurotransmitters, and compromised gut motor function including delayed gastric emptying and intestinal transit.

These anomalies have been found to self-correct once microbial populations are restored. A study conducted in middle-aged rats found significant improvement in spatial memory after supplementation with probiotics and prebiotics as well as increased BDNF levels - a brain-derived neurotrophic factor associated with improved memory and cognition. BDNF also plays an important role in muscle repair and regeneration. Whereas germ-free animals are reported to display memory dysfunction due to altered levels of BDNF. 

Further associations have been made between microbiota and mood disorders with the use of probiotics and antibiotics and their resultant impact on mood disorders. Reduced levels of gamma-aminobutyric acid (GABA) are associated with anxiety and depression disorders. Consistent long-term treatment with Lactobacillus rhamnosus JB-1 was found to have altered GABA expression in the brain and reduced anxiety and depression behavior in mice.  Studies in germ-free animals support the idea that microbiota influences stress reactivity and anxious behavior. Digestive disorders occur alongside mood disorders and reflect an imbalance in gut bacterial diversity. Probiotics reduced stress-induced cortisol release as well as anxiety and depression symptoms. Probiotic supplementation has also been associated with increased levels of BDNF expression in the brain.

Does intestinal microbiota influence how you feel?
Before we dive into how gut microbes might influence how you feel, let’s peek into how sensory and motor information travels between the gut and the brain.

Taking over the second brain - the enteric nervous system
The enteric nervous system (ENS) which regulates digestive functions contains about 100 to 500 million neurons, meaning it has more neurons than the spinal cord. 

The ENS, also known as the second brain, is a major source of sensory information for the brain. The vagus nerve travels from the brainstem to the abdomen and connects to the intestinal wall and ENS, making it the fastest way for gut-brain signaling. The gut microbiota influences the ENS and subsequently CNS by interacting with the intestinal cells as well as additional hormonal and metabolic pathways.

Microbiota - a neurotransmitter production unit
A study in mice revealed subjects with a surgically removed vagus nerve did not display neurochemical and behavioral communication associated with microbiota-led vagus nerve communication, marking the vagus nerve as an important link for gut-brain communication.

The gut microbiome might also affect mood by influencing food choices by manipulating vagus nerve signaling via peptides and releasing microbial serotonin to influence behavior. Neurotransmitter precursors travel to the brain from the gut and cross the blood-brain barrier and are directly utilized by the brain for the local synthesis of additional neuroactive compounds.  A healthy gut microbiome promotes a tightly packed gut barrier that doesn’t allow pathogens or bacterial toxins to pass into blood circulation via the intestinal lining or across the blood-brain barrier (BBB). Stress and depression can increase gut barrier permeability allowing for toxic metabolites to pass through the gut lining leading to a heightened inflammatory response by the immune system. Stress and depression might also prompt unhealthy food choices due to the increased dominance of pathogenic bacteria.

Can the gut microbiome have neuroprotective or neurodegenerative effects?
The gut microbiome has the potential to alter and influence essential neurological functions. We’re already aware of the role of neuroactive metabolites such as neurotransmitters and precursors. 

But the impact of microbiota becomes more extensive due to the action of pro-inflammatory and anti-inflammatory immune responses based on the state of the gut health and the dominance of probiotics or pathogens in the gut. 
Following this line of thought, it begs the question that if a healthy microbiome leads to optimal brain health, how does dysbiosis or an imbalance in the gut microbiome express itself?

Microbiota - neurodegenerative or neuroprotective?
Your brain has a high metabolic rate and as a result, it produces high levels of free radicals which is on par with metabolic activity and enzymatic processes. In a healthy individual, free radicals are neutralized by antioxidants and the cycle continues. 

But in the event of an imbalance between free radicals and antioxidants, free radicals such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) can lead to oxidative stress and damage resulting in neuroinflammation, cell damage, and cell death. Gut dysbiosis and neuroinflammation are common factors across various neurodegenerative diseases. Dysbiosis leads to a pro-inflammatory response in the body and brain and decreases the anti-inflammatory response which in turn leads to more oxidative damage, the formation of neurotoxin clumps such as Aβ plaques in Alzheimer’s leading to neurodegeneration. Degeneration of doperminergic neurons is a disease marker in Parkinson disease (PD).  There’s increasing evidence that gut microbiota plays a critical role in the development of Parkinson’s disease (PD).  In a study conducted in PD mice, supplementing with bifidobacterium breve CCFM1067 for 5 weeks protected doperminergic neurons and suppressed neuroinflammation. Additionally, there was an increased antioxidant capacity of the central nervous system and reduced oxidative stress. Co-supplementation of probiotic and selenium for 12 weeks in 79 Alzheimer patients in a randomized, double-blind, controlled clinical trial showed an improvement of cognitive and metabolic functions. Research evidence suggests a strong association between dysbiosis and various neurological disorders such as Alzheimer's, Parkinson’s, Autism spectrum disorder (ASD), Amyotrophic lateral sclerosis (ALS), epilepsy, and major depressive disorder (MDD). On the other hand, a healthy gut microbiome produces metabolites that have an antioxidant and anti-inflammatory effect, positively affects cognitive function and maintains the gut barrier and blood-brain barrier integrity. Numerous studies have shown that probiotics strains such as B. longum, L. rhamnosus, L. casei have improved functions such as memory and learning, mood and feeling of well being in animal models.

Altering gut health to enhance mental health - has it been done? 
A randomized, double-blind, placebo-controlled, multicenter trial conducted in 63 older adults over the age of 65 found that probiotic supplementation led to a decrease in inflammation-causing gut bacteria, an increase in mental flexibility, and improved stress score as well as an increase in brain-derived neurotrophic factor (BDNF).

Another review article published in the World Journal of Pharmaceutical and Life Sciences found that probiotic supplementation with strains such as L. acidophilus, L. rhamnosus, L. helveticus, B. longun, B. bifidum, and B. infantis may result in improving physiological and psychological diseases.



Probiotics and brain health
The gut microbiome is a complex and delicate system that is easily influenced by genetics, diet, stress, and lifestyle stressors. With more and more studies pointing towards associations between gut, mental and digestive health, the role of probiotics as a possible support option is gaining momentum.

So far the cause and effect - whether a neurological disorder induces dysbiosis or it's the other way around is still being investigated. But there’s rapidly emerging evidence on the impact of gut microbiome in the development of neural development, modulating neurotransmission and as a result cognitive behavior. 

A diverse gut microbiome is suggested to confer a protective health effect on the host. A fiber and probiotic rich diet might be one of the fastest ways to affect a positive shift  in the gut microbiome. Along with supplementing with probiotics rich in strains such as B. bifidum, B. longum, L. plantarum and L. reuteri, all of which are included in our Sugar Shift formula, might give your gut microbiome a push in the right direction. 

With gratitude,

Martha Carlin photo Martha Carlin, is a “Citizen Scientist”, systems thinker, wife of Parkinson’s warrior, John Carlin, and founder of The BioCollective , a microbiome company expanding the reach of science and BiotiQuest, the first of it’s kind probiotic line. Since John’s diagnosis in 2002, Martha began learning the science of agriculture, nutrition, environment, infectious disease, Parkinson’s pathology and much more. In 2014, when the first research was published showing a connection between the gut bacteria and the two phenotypes of Parkinson’s, Martha quit her former career as a business turnaround expert and founded The BioCollective to accelerate the discovery of the impact of gut health on all human disease. Martha was a speaker at the White House 2016 Microbiome Initiative launch, challenging the scientific community to “think in a broader context”. Her systems thinking background and experience has led to collaborations across the scientific spectrum from neuroscience to engineering to infectious disease. She is a respected out of the box problem solver in the microbiome field and brings a unique perspective to helping others understand the connections from the soil to the food to our guts and our brains.

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