Gut health and mental health: understanding the gut–brain connection

The gut and brain are closely connected through a communication system known as the gut-brain axis. This system links digestion, immune function and brain activity.

Within this system, the gut microbiome plays an important role in signalling, inflammation and overall wellbeing. Because of this, gut health may influence how we feel, including mood, stress and anxiety. However, it is often overlooked in conversations about mental wellbeing.

Growing evidence suggests that disruptions in gut health are associated with conditions such as depression and anxiety. Although many mechanisms are still being explored, the gut is increasingly recognised as an active part of a wider system that shapes how the body and brain respond to stress.

In this blog, we explore how the gut-brain axis works, how gut health may influence mental health, and practical ways to support it.

What is the gut-brain axis?

The gut-brain axis is a two-way communication system linking the central nervous system with the digestive system. Signals travel in both directions, meaning the gut can influence the brain, and the brain can influence gut function.

How the gut and brain communicate
Communication happens through several interconnected pathways:

The vague nerve (direct signalling between gut and brain)
The immune system (inflammatory signalling)
Hormones involved in the stress response
Chemical messengers such as neurotransmitters (e.g. serotonin) and their precursors

Most of the body’s serotonin is produced in the gut, where it mainly helps regulate digestion. Although this serotonin does not directly enter the brain, the brain produces its own serotonin from tryptophan, an amino acid obtained from food. The gut microbiome may influence this process by affective tryptophan availability, as well as through immune signalling, inflammation and the vagus nerve.

The microbiome may also influence compounds such as GABA, which helps regulate and calm brain activity, and dopamine, which is involved in motivation, reward and enjoyment.

Together, these pathways suggest that the gut is part of a wider system of interacting processes involved in mood, stress and emotional regulation.

Microbiota vs microbiome: what's the difference?

These terms are closely related but not the same:
Microbiota refers to the community of microorganisms living in the gut, including bacteria, fungi and viruses
Microbiome refers to these microorganisms, along with their genes and the functions they perform

A simple way to think about it:

Microbiota – the microorganisms
Microbiome – the microorganisms and what they do

How the gut microbiome works

The gut microbiome contributes to several key processes, including:

Influencing compounds involved in brain signalling, such as neurotransmitter serotonin
Producing short-chain fatty acids (SCFAs), created when bacteria break down fibre. These help regulate inflammation and support gut and brain function
Supporting immune system activity
Maintain the gut lining

Why microbial diversity matters
Gut health can be disrupted when the balance of microbes changes, a process known as dysbiosis. This imbalance is often influenced by diet, stress, poor sleep and environmental exposures.

The gut lining acts as a barrier, controlling what enters the bloodstream. When this barrier is disrupted, it may become more permeable, sometimes referred to as increased intestinal permeability. This may allow bacterial components, food proteins and other molecules to enter the bloodstream more easily.

This can contribute to chronic low-grade inflammation and may alter signalling processes linked to brain function. At the same time, the production of beneficial compounds such as SCFAs may be reduced.

How gut health is linked to mental health

Growing research suggests that gut health may influence mental health through several interacting pathways:

1. Neurochemical signalling
The gut microbiome influences compounds such as serotonin, dopamine and GABA, which are involved in mood and emotional regulation. Disruptions may therefore influence how these systems function.

2. Immune and inflammatory pathways
Changes in gut barrier function and microbial balance may contribute to inflammation, which can affect brain function and stress responses.

3. Stress response systems
The gut interacts with the body’s stress system. Changes in gut health may influence how the body responds to stress, while chronic stress can also affect gut function.

4. Cognitive and emotional processes
Gut health has been linked to experiences such as low mood, anxiety, increased stress sensitivity and difficulty regulating emotions.
These pathways interact and reinforce one another rather than operating in isolation. Gut health is best understood as part of a wider system that can influence vulnerability, severity and recovery over time, rather than as a single cause of mental health conditions.

Emerging research
Research in this area is developing rapidly. Studies have found that people experiencing depressive symptoms often have lower microbiome diversity, although it is not yet clear whether this is a cause, a consequence, or part of a broader set of interacting factors.

The gut microbiome may also influence cognitive and emotional patterns, such as stress sensitivity and rumination. These effects are thought to involve a combination of biological pathways including inflammation, stress signalling and communication along the gut–brain axis.

Importantly, this relationship appears to work in both directions. Changes in gut health may influence brain function and mental wellbeing, while psychological factors such as chronic stress and low mood can also affect the gut microbiome

What can disrupt gut health?

Several factors can negatively affect the gut microbiome:

Diet

Diets high in ultra-processed foods are associated with poorer gut health. These foods are often low in fibre and high in additives which may reduce beneficial bacteria and affect the gut lining
High sugar intake may encourage less beneficial bacteria and contribute to inflammation
Research suggests that artificial sweeteners may alter microbial composition in some individuals
Low fibre and low dietary diversity reduce beneficial bacteria

Overall dietary patterns matter more than individual foods, as the microbiome responds to long-term habits rather than short-term changes.

Stress
Chronic stress can disrupt gut health in several ways. It may:

Alter gut motility (how quickly food moves through the gut)
Reduce blood flow to the digestive system
Influence microbial composition (the diversity and abundance of microorganisms)
Increase gut permeability

Sleep
Poor or disrupted sleep may:

Alter microbial balance and daily rhythms
Increase inflammation
Affect how the body regulates energy and metabolism

The relationship also appears to work both ways, as the gut microbiome may influence processes linked to sleep.

Physical activity
Regular movement is associated with:

Greater microbiome diversity
Increased production of beneficial compounds such as SCFAs
Improved immune and metabolic function

Environment

Environmental exposures, including aspects of the food system, can influence gut health
Access to affordable nutritious, fibre-rich food plays a major role in shaping the microbiome

How to support gut health for better mental wellbeing

Food and nutrition

Prioritise dietary diversity
Eating a wide variety of plant-based foods supports a more diverse microbiome. Some research suggests that aiming for around 30 or more different plant types each week may support greater diversity.
Increase fibre intake
Fibre feeds beneficial bacteria. Sources include vegetables, fruit, legumes, wholegrains, nuts and seeds.
Include fermented foods
Fermented foods, such as live yoghurt, kefir and kimchi, contain live microorganisms and may support microbial diversity in some people.
Focus on overall diet quality
Diets high in ultra-processed foods and added sugars are associated with lower diversity and increased inflammation.
Be mindful of other factors
Alcohol, additives and antibiotics may affect the microbiome, although responses can vary between individuals.
Support access and opportunity
Access to affordable, nutritious food is essential. Schools, community organisations and wider systems play an important role in improving access to healthier choices, alongside building knowledge and confidence around making food choices that support mental wellbeing.

Lifestyle factors

Prioritise consistent, good-quality sleep
Manage stress where possible
Engage in regular physical activity

Spend time outdoors

Time in natural environments is associated with improved wellbeing and may support gut health through reduced stress, improved sleep and physical activity, as well as exposure to a wider range of beneficial environmental microbes.

Consistency matters

Small, consistent changes are more effective than short-term approaches. Diet, sleep, stress and activity all interact, so gradual improvements are more likely to be sustained.

Conclusion

The gut–brain axis highlights how gut health is embedded within a wider system that can shape mental health. The gut microbiome contributes to processes linked to mood, stress, immune signalling and inflammation, influencing how the body and brain respond to challenges over time.

Disruptions to gut health may affect both physical and mental wellbeing, although mental health is shaped by many interacting biological, psychological and social factors.

Supporting gut health may therefore contribute to better mental wellbeing, particularly when combined with broader approaches that address diet, sleep, physical activity, stress, environment and access to healthy food. Gut health is not a single solution, but one important part of a wider system that shapes mental health over time.