Gut Superpowers: The Role of the Gut Microbiome in Health

From newspaper headlines to new food product launches, social media posts and book releases, there seems to be heightened interest in caring for and understanding our gut microbiome. Despite sounding like yet another wellness buzzword, this trend arguably has more robust science behind it than previous wellbeing trends.

When we think of gut health, we naturally focus on digestion – but it doesn’t stop there. The gut microbiome is emerging as a pivotal conductor in human health.  Research continues to unveil the intricate crosstalk between this complex and dynamic community of microorganisms (Box 1) and various organs and systems, far beyond its ‘traditional’ role in digestive health. It influences everything from immune function to mental wellbeing (Figure 1). Understanding these multifaceted interactions, orchestrated by the gut microbiome, is an exciting opportunity to further advance patient care.

There is no core “healthy” microbiota that is common to all individuals – in fact, our gut microbiota is as unique as our fingerprint. Nevertheless, there are three characteristics that are considered key: diversity, stability and resilience.¹ Studies have shown that these characteristics are associated with healthy long-living people² and the absence of certain gut microbiota-associated diseases.^1,3-5

Have you ever felt “butterflies” in your stomach or experienced gastrointestinal (GI) symptom flare up during times of anxiety or stress? That’s the gut-brain connection instinctively in action. The ‘gut-brain axis’ describes the bidirectional communication between the central nervous system (i.e., the brain) with the enteric nervous system (ENS) of the gut; the ENS is commonly referred to as our “second brain”.

Communication between the gut and the brain primarily takes place via the vagus nerve.^6-7 Amazingly, 80% of the neurons in the vagus nerve convey information “up” from the intestinal wall to the brain.⁸ Besides these neurological routes, there are also other pathways that allow for communication between the gut and brain such as via endocrine, metabolic and immune systems. It is thought that there are more pathways but we are still learning about these and their impact.

Irritable bowel syndrome (IBS), a common GI disorder affecting between 5-20% of the general population, is now recognised as a condition of the gut-brain axis.⁹ Those living with IBS and other conditions such as Alzheimer’s disease,¹⁰ autism¹¹ and Parkinson’s disease¹² have a different gut microbiota composition (including less diversity) compared to healthy individuals which may influence disease occurrence and progression. Accumulating gut-brain research is revealing new possibilities for dietetic and cognitive-based therapies to target both mental health and GI conditions, including the use of psychobiotics e.g., probiotics that could offer mental health benefits.^13-14

 

Fact checker: More than 90% of the “happy hormone” is produced in the gut

You may have heard that approximately 95% of serotonin, a key neurotransmitter in regulating mood often dubbed the “happy hormone”, is produced in the gut.^15-16 However, this doesn’t tell the whole story. It’s unlikely that serotonin can cross the blood-brain barrier.¹⁷ Instead, the precursor molecule, tryptophan can cross this blood-brain barrier, therefore indirectly modulating serotonin production and function.¹⁸ The gut microbiota influences the metabolism of tryptophan and it can also be found in some foods (e.g., bananas, poultry, oats and chocolate).

 

Learn more in our gut-brain HCP resource here. 

Our gut health and immune health are closely linked, meaning an imbalance in one can affect the other. Amazingly, 70-80% of immune cells are in the gut¹⁹ where they are trained to react and differentiate between “innocent bystanders” and harmful “real culprits” in the body – think of your gut microbiota as the teacher and immune cells as the students.

Research shows gut bacteria and their metabolites (e.g., short-chain fatty acids) have an important role in immune development and homeostasis, and communicate with immune cells via direct and indirect pathways:^19-23

• Gut microbiota indirectly supports the immune system by optimising food digestion, thus ensuring the full nutritional benefits are obtained from foods consumed e.g., fermentation of dietary fibre, synthesis of vitamins and absorption of nutrients.
• Gut microbiota supports biotransformation whereby toxic chemical compounds are biochemically modified into less toxic forms.
• Gut epithelial cells, reinforced by a mucus lining, provide a barrier to bacterial invasion.

Simultaneously, the immune system maintains microbial balance and regulates healthy microbe colonisation.

 

Learn more in our gut-immune HCP resource here. 

Like our gut, our skin is host to an array of microorganisms. The exact composition varies between individuals and depending on the location of skin.

The ‘gut-skin axis’ describes the bidirectional relationship whereby the gut microbiome may influence the condition of the skin and vice versa. Evidence of this interaction is seen in food allergies manifesting as skin symptoms such as urticaria, atopic dermatitis or, in the case of coeliac disease, dermatitis herpetiformis.²⁴ On the other hand, vitamin D₃ is synthesised in the skin when exposed to UVB radiation, which can influence the diversity of the gut microbiota.²⁵ Emerging evidence suggests oral probiotics, prebiotics and synbiotics (a mixture of probiotics and prebiotics) may improve some skin conditions such as eczema and acne via gut microbiome modulation.²⁶ Proposed mechanisms for the gut-skin axis include intestinal barrier, inflammatory mediators and metabolites such as short-chain fatty acids.²⁴

At Yakult Science for Health, we are currently collaborating with King’s College London on a scoping review investigating the impact of probiotics, prebiotics and synbiotics on skin outcomes via the gut microbiome. The results of this review are expected to be published in Spring 2025 – watch this space!

Metabolism plays a fundamental role in our overall health. It involves a range of complex biochemical reactions and processes that occur within all cells of the human body.

The gut microbiome influences metabolism through the regulation of gut hormone release. Specifically, bacteria in the gut microbiota communicate to specialised enteroendocrine (EE) cells in the mucosal lining of the gut via microbial metabolites (e.g., short-chain fatty acids, secondary bile acids, structural components).²⁷ EE cells then secrete hormones (e.g., CCK, PYY, GLP-1, GIP, 5-HT) which influence insulin sensitivity, glucose tolerance, fat storage and appetite (Figure 2).

 

Learn more in our gut-metabolism HCP resource here. 

Research is now exploring whether modulation of the gut microbiota could have implications on disease onset and progression relating to the gut-brain, gut-immune, gut-metabolism and gut-skin axes.

Observational data shows that dysbiosis of the gut microbiota (i.e., imbalance) is associated with various conditions including:

• IBS⁹
• Alzheimer’s disease¹⁰
• Autism¹¹
• Parkinson’s disease¹²
• Obesity²⁸
• Type 2 diabetes²⁹
• Acne³⁰
• Eczema³¹
• Psoriasis³²
• Rosacea³³

Much of the evidence currently comes from observational studies which cannot demonstrate causality (Figure 3). This opens up the famous chicken-or-egg conundrum: which came first? It remains unknown whether an imbalanced gut microbiota (dysbiosis) precedes the condition or vice versa. More research is needed to better understand whether gut dysbiosis may cause, or contribute to the development of certain conditions, or whether the condition itself reduces microbial diversity.

By now you hopefully have an increased appreciation for the intricate and varied role of the gut microbiota. It’s clear we should be optimising our gut health to support overall wellbeing – but how exactly can this be achieved?

There are certain non-modifiable factors that affect the diversity of the gut microbiota, such as age and genetics. However, there are many which we do have control over, including diet, exercise, sleep and mindfulness (Figure 4). Better yet, the gut microbiota composition can be altered within a matter of weeks, and even days when focusing on the simple diet and lifestyle changes below (although there is both intra- and inter-individual variation).³⁴ 

1. Diet: What we eat is key to shaping the gut microbiota – it is one of the most important easily modifiable factors determining which bacterial species reside in the gut.^35-36 Focus on prioritising plant diversity within the diet (i.e., fruit, vegetables, wholegrains, nuts and seeds) to promote fibre intake which is well-researched and shown to increase gut microbiota diversity.³⁷ As research continues in this area, diets targeting the gut microbiota to introduce or eliminate specific bacterial species, could prove a powerful avenue for realising the possibilities of improving health through nutrition.
2. Exercise: Exercise independently increases the diversity of your gut microbiota and increases the growth of beneficial bacteria in the gut, both of which can support immune function.³⁸
3. Sleep: Irregular sleep patterns are associated with poorer diet quality, inflammation and reduced gut microbiota diversity.³⁹ Getting enough good quality sleep could improve your gut health, and vice versa.
4. Mindfulness: Mindfulness is the act of being intentionally present, allowing us to feel calmer and less stressed.⁴⁰ It has been associated with improved physical, mental and gut health.⁴¹ Mindfulness can alter the gut microbiota composition in a way that could help to reduce symptoms of anxiety and depression (the gut-brain axis in action!).⁴¹

 

Can we call the gut microbiota the “conductor of health”?

The gut microbiota plays a key role in conducting the orchestra of different organs and systems. Are we on the verge of uncovering the “gut-everything” axis?

By understanding and harnessing the far-reaching role of the gut microbiota, we can unlock its potential to support the prevention and management of certain conditions and diseases. In fact, recognising and leveraging its ability to shape and optimise health outcomes may even revolutionise patient care and make gut health a cornerstone of modern medicine.

 

Learn more in our Get to Know the Gut HCP resource here. 

1. More than a gut feeling: Gut health doesn’t only equate to digestive health.
2. Gut-brain axis: The enteric nervous system of the gut and the central nervous system communicate via neurological, endocrine, metabolic and immune system pathways.
3. Gut-immune axis: The gut microbiota trains, educates and constantly communicates with the immune cells situated in the gut to support long-term immunity.
4. Gut-skin: An altered gut microbiome may influence the onset and development of skin conditions such as eczema and acne.
5. Gut-metabolism: The gut microbiome influences metabolism through the regulation of gut hormone release and may play a role in metabolic syndrome.
6. Back to basics: Prioritise a diverse diet, regular exercise, good quality sleep and minimising stress to support gut health.

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