Did you know that the gut is known as your second brain? Have you ever wondered why? Here, we investigate the mechanisms behind how your gut community can influence your mental wellbeing and brain function.
Content Outline
- What is the Gut-Brain Axis?
- How Gut Microbes Influence the Brain
- The Role of Probiotics, Prebiotics, and Postbiotics in the Gut-Brain Axis
- Supporting Mental Health Through Gut Health: Top Tips
- Summary
What is the Gut-Brain Axis?
The gut-brain axis is a unique, bidirectional communication pathway, along which gut bacteria can influence brain function, and potentially impact mental health and cognition1.
It is a network of communication between the gastrointestinal tract and the central nervous system. It involves the nervous, endocrine (hormonal), and immune pathways and can influence many functions in the body and the development of several diseases.
In short, the gut-brain axis is a physical and biochemical connection between both organs.
How Gut Microbes Influence the Brain
There are trillions of microbes residing in your gut – collectively known as the gut microbiota – that play a critical role in brain function, mental health, and cognition.
The microbes, particularly bacteria, influence the brain through several interconnected pathways, including through neurotransmitter production, inflammation regulation, and gut permeability.
Microbes and neurotransmitter production
Neurotransmitters are chemical messages that are sent between nerve cells and other cells like muscles and glands2. There are many different neurotransmitters produced by the body which have various functions, but several neurotransmitters that regulate mood and cognition are produced by the gut, such as:
- Serotonin – often called the ‘happy’ hormone, around 95% of the body’s serotonin is provided by the gut3. SCFAs can regulate the release of serotonin from enterochromaffin cells and certain Lactobacillus strains can enhance gut-derived serotonin sythensis4.
- Gamma-aminobutyric acid (GABA) – involved in regulating stress and anxiety, GABA production can be increased by probiotic strains such as Lactobacillus plantarum L55.
- Dopamine – a key neurotransmitter involved in motivation and pleasure, dopamine production is heavily influenced by the gut and can influence motility, mucosal barrier function, and neurological conditions6.
Gut microbiota, inflammation, and brain health
A balanced gut microbiota can regulate your immune system and prevent chronic inflammation, a key contributor to mental health and cognitive disorders.
An imbalanced microbiome, also known as dysbiosis, is where an overabundance of harmful bacteria can trigger an inflammatory response, releasing pro-inflammatory molecules, like cytokines6.
Pro-inflammatory signals and cytokines can negatively impact brain health by:
- stimulating premature brain and cognitive aging7
- enhancing the progression of neurodegenerative disease, especially in older adults8
- increasing the production of neurotoxic metabolites9 such as lipopolysaccharide (LPS), an inflammatory toxin that can pass into the blood through a leaky gut. High LPS levels have been associated with dementia, depression, and schizophrenia
Gut permeability
The gut lining is a protective barrier, preventing harmful substances from entering the bloodstream. However, if the gut microbiota is imbalanced, the barrier can weaken, leading to increased permeability, often called a ‘leaky gut’.
When pathogenic bacteria and toxins enter the blood, they can trigger systemic inflammation and affect brain function. Research suggests that increased gut permeability can trigger or worsen:
- mood disorders like anxiety and depression10
- cognitive decline and neurodegenerative conditions including Alzheimer’s and Parkinson's diseases11
- stress-related conditions12
The Role of Probiotics, Prebiotics, and Postbiotics in the Gut-Brain Axis
Because brain and mental health are heavily influenced by the gut microbiota, there is a chance that changing its composition may improve your health.
There are several ways that this can be done, including:
- increasing your probiotic intake
- feeding your beneficial gut bacteria with prebiotics
- improving your lifestyle
Let’s explore some of the ways probiotics, prebiotics, and their postbiotics can support your brain health and cognitive function.
Probiotics: The Beneficial Bacteria
Probiotics, like Lactobacilli and Bifidobacteria, are beneficial bacteria that can positively influence the gut-brain axis and support mental health and wellbeing.
Some of the specific strains that have been linked to brain health are:
Lactobacillus rhamnosus
- During a 3-month intervention where participants aged between 52 and 75 were given a daily supplement of L. rhamnosus or a placebo, improvement in cognition was established in older adults with cognitive impairment in the probiotic group13.
- A further study investigated the effects of L. rhamnosus on spatial memory and cytokine expression in an inflammation-based Alzheimer’s disease model and found that this strain can positively benefit cognitive deficit and neuroinflammation, lowering the expression of pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-α)14.
Bifidobacteria longum
- B. longum is a strain that can have a positive effect on stress and memory15. Further studies have shown that it can enhance vitality and reduce mental fatigue16.
- B. longum has previously been shown to positively affect stress-, anxiety-, and depression-related behaviour in pre-clinical animal studies17.
Lactobacillus plantarum
- Research shows that some strains have protective effects against memory function decline in adults over 65 years after a 12-week intervention18.
- Other strains of L. plantarum improve cognition and may improve mood and sleep19.
Prebiotics: Fuel for the Microbiome
Prebiotics are non-digestible fibers that feed beneficial gut bacteria and can affect the gut-brain axis by:
- affecting mood
- positively benefitting behaviour
- improving cognitive function
Several different types of prebiotics are available which can nourish probiotics, including:
- fructooligosaccharides (FOS)
- galactooligosaccharides (GOS)
- human milk oligosaccharides (HMOs)
- resistant starch
One study found that a daily 5g dose of GOS and eicosapentaenoic acid at no more than 1g can effectively alleviate depression symptoms20. It does this by increasing the production of neurotransmitters and short-chain fatty acids (SCFAs), regulating inflammation.
HMOs and Their Potential Role in Mental Health and Cognition
Human milk oligosaccharides (HMOs) are a type of prebiotic fiber that are found in breast milk that promote the growth and activity of specific probiotic species.
While HMOs are primarily recognized for their role in infant health and immune function, emerging research suggests they have potent neurological and cognitive benefits, that extend beyond infancy into adulthood. For example, sialylated HMOs, like 3’sialyllactose (3’SL) and 6’sialyllactose (6’SL), are important for myelination and the health of neurons or nerve cells21 and for supporting cognitive development in infants22.
HMOs can further contribute to mental wellbeing and cognitive function through its interaction with the gut-brain axis. They selectively feed beneficial gut bacteria, especially Bifidobacteria strains which also cross-feed other bacteria species, such as butyrate producers, like Faecalibacterium prausnitzii.
Butyrate is the least produced SCFA by the gut, but arguably has the biggest impact. It’s the primary fuel source for colonocytes, the cells that line the gut, strengthening the integrity of the gut barrier and regulating the immune system23.
However, animal studies have shown that it can improve the status of Alzheimer’s disease, revealing its potential as a therapeutic treatment in the future24.
Some of the further benefits of HMOs on mental health include:
- reducing stress and anxiety
- improving mood
- supporting cognitive function and memory
- enhancing gut barrier integrity
While research is still emerging to establish the important link between HMOs and adult brain function, so far, studies suggest they have promising potential and, in the future, HMOs could become a novel psychobiotic ingredient for brain health supplements.
What are psychobiotics?
You may have heard the term psychobiotics and are unsure what that means. Psychobiotics are probiotics or prebiotics that directly benefit mental health. They can do this by various mechanisms, such as:
- influencing neurotransmitter production
- reducing inflammation
- regulating stress responses to strengthen the integrity of your gut barrier
HMOs like 3’SL and 6’SL are specialised forms of sialic acid, a naturally occurring sugar that’s important for many biological functions. It’s particularly critical for brain health, forming connections between nerve cells, but has also been found to have protective benefits against neurodegeneration23.
Supporting Mental Health Through Gut Health: Top Tips
Optimizing and prioritizing gut health is a powerful way to support your mental wellbeing and invest in your future cognitive function. By incorporating dietary and lifestyle strategies into your daily routine, you can nurture a balanced gut microbiota, reduce inflammation, and enhance neurotransmitter and metabolite production.
Here are some of the practical things you can do to enhance your gut-brain communication and support long-term mental health:
- Eat a fiber rich diet that incorporates prebiotic foods like bananas, onions and chicory to nourish your health-promoting bacteria species.
- Consume probiotic-rich foods like yogurt, kefir, kimchi, and natto.
- Explore psychobiotic supplements to target gut-brain support such as SuperHMO® Prebiotic Mix with 5 HMOs.
- Consider HMOs as an emerging tool to support your mental health and wellbeing, like PureHMO Prebiotic Powder
- Try probiotics that strengthen your gut barrier lining like the Akkermansia muciniphila Daily Probiotic or our SuperHMO® Synbiotic that combines 5 potent HMOs with 10 key probiotic strains to help boost cognitive function.
Summary
The gut-brain axis is a critical link between your gut microbiota and your brain, influencing your mental health and cognitive function. By nourishing the gut with the right prebiotics and probiotics, you’ll be making a long-term investment in your brain health, mood, and lowering your risk of mental health conditions.
As new research continues to emerge, gut-targeted therapies are going to become a key strategy for supporting mental wellbeing and cognitive longevity. So, optimizing gut health isn’t just good for digestion, but it’s essential for your brain too.
Written by: Leanne Edermaniger, M.Sc. Leanne is a professional science writer who specializes in human health and enjoys writing about all things related to the gut microbiome.
