By: Umm E Hani Waheed, dietetic student-volunteer, reviewed by Natalie Walsh, RD, and the JM Nutrition Team
The Powerful Gut–Brain Axis
Introduction
For many years, experts studied mental health and digestive health separately. However, research now shows that these systems are closely connected (Cryan et al., 2019).
Therefore, scientists now focus on the gut–brain axis. This is a communication network between the gastrointestinal tract and the central nervous system (Cryan et al., 2019).
At the centre of this system lies the gut microbiome. It includes trillions of bacteria, fungi, viruses, and other microorganisms in the digestive tract (Cryan et al., 2019).
Emerging research suggests these microbes influence mood, stress response, cognition, and mental well-being (Cryan et al., 2019). Although the field is still developing, evidence continues to grow.
In addition, lifestyle and diet appear to play an important role in shaping this system.
What Is the Gut Microbiome?
The gut microbiome is a complex ecosystem of microorganisms in the digestive system. These organisms perform essential functions (Cryan et al., 2019).
They:
- Break down fibre and nutrients.
- Produce vitamins, including vitamin K and B vitamins.
- Support immune function.
- Help protect against harmful pathogens.
- Produce metabolites that influence body systems (Cryan et al., 2019).
A healthy microbiome shows diversity and balance. Furthermore, higher diversity is generally linked with better health outcomes (Cryan et al., 2019).
A Closer Look at the Gut–Brain Axis
Nutrient connections
The gut supports brain health through nutrient absorption. For example, low levels of omega-3 fatty acids and B vitamins are linked with mood and cognitive changes.
Therefore, diet quality directly affects brain function.
Digestive conditions and mood
Research shows a connection between digestive disorders and mental health conditions. For instance, individuals with IBS often report higher rates of anxiety and depression (Cryan et al., 2019).
Related: dietary support for IBS
In addition, chronic digestive symptoms may increase psychological stress.
Antibiotics and microbiome changes
Antibiotics treat harmful bacteria. However, they also reduce beneficial microbes, disrupting microbial balance (Cryan et al., 2019). As a result, some people report mood changes after antibiotic use.
Stress and gut changes
Stress affects appetite and alters the gut microbiome. In turn, these changes may influence mood and emotional regulation (Cryan et al., 2019). Therefore, the relationship works in both directions.
Related: Cortisol-Lowering Foods for Stress Management
Psychobiotics and emerging research
Some probiotic strains may support mental health. These are sometimes called psychobiotics (Dinan et al., 2013).
Examples include:
- Lactobacillus rhamnosus
- Bifidobacterium lactis HN019
However, research remains ongoing, and results vary between individuals.
How the Gut and Brain Communicate
Nervous system pathways
The gut contains a large network of neurons known as the enteric nervous system. It is often called the “second brain” (Cryan et al., 2019). In addition, it contains millions of nerve cells. These cells regulate digestion, movement and enzyme release.
What’s more, the vagus nerve connects the gut and brain directly. It functions as a major communication pathway (Cryan et al., 2019).
Furthermore, most signals travel from the gut to the brain. This highlights the gut’s influence on brain function (Cryan et al., 2019).
Immune and inflammatory pathways
The gut also houses a large portion of the immune system. This makes sense because the digestive tract is exposed to external substances.
When the immune system responds to threats, it can trigger inflammation. If inflammation becomes chronic, it may affect mood and brain function (Cryan et al., 2019).
Therefore, immune activity forms another key link between gut and mental health.
Mood and Food Connections
Nutrition plays a direct role in gut and brain health. This field is known as nutritional psychiatry.
Research shows that healthy dietary patterns reduce the risk of depression and anxiety. Therefore, diet acts as a modifiable risk factor (Jacka et al., 2017).
Supportive dietary components include:
- Fruits and vegetables
- Whole grains
- Legumes, nuts, and seeds
- Fish, poultry, eggs, and lean meats
- Olive oil
In contrast, highly processed foods are linked with poorer mental health outcomes. These include sugary foods, fried foods, and ultra-processed meals.
Evidence from Research
The SMILES trial examined dietary change in individuals with depression (Jacka et al., 2017). Participants who improved their diet reported significant improvements in depressive symptoms over 12 weeks (Jacka et al., 2017).
Therefore, dietary quality may support mental health alongside other treatments.
Practical Ways to Support Gut and Mental Health
Increase fibre intake
Fibre supports beneficial gut bacteria and promotes short-chain fatty acid production (Cryan et al., 2019).
Good sources include:
- Fruits and vegetables
- Whole grains
- Legumes
- Nuts and seeds
Include fermented foods
Fermented foods introduce beneficial microbes and may support microbial diversity (Cryan et al., 2019).
Examples include yogurt, kefir, kimchi, sauerkraut, miso, and tempeh.
Reduce processed foods
Highly processed foods may reduce microbial diversity and increase inflammation (Cryan et al., 2019). Therefore, reducing intake may support both gut and mental health.
Manage stress
Stress directly affects the gut–brain axis and microbial composition (Cryan et al., 2019).
Helpful strategies include:
- Physical activity
- Meditation
- Deep breathing
- Outdoor time
- Social connection
- Adequate rest
Prioritize sleep
Sleep supports both brain and gut function. Poor sleep may disrupt microbial balance (Cryan et al., 2019). Most adults benefit from seven to nine hours of sleep per night.
Related: Nutrition Tips for Better Sleep
Use probiotics carefully
Some probiotic strains show potential benefits for mental health (Dinan et al., 2013). However, effects vary and more research is needed. Therefore, probiotics should not replace medical care.
Conclusion
The gut and brain function as a connected system. They communicate through neural, immune, and biochemical pathways (Cryan et al., 2019). Therefore, changes in one system can influence the other.
Current research shows that the gut microbiome plays an important role in mood regulation, stress response, and cognitive function (Cryan et al., 2019). In addition, diet, sleep, and stress levels all influence this system.
Although research is still developing, evidence suggests that supporting gut health may also support mental well-being (Jacka et al., 2017).
Ultimately, this connection highlights the importance of a holistic approach. Mental health and physical health operate as one integrated system rather than separate domains.
Should you feel you require personalized sessions with a dietitian for gut health or support for mental health concerns, book a free consultation or contact us for an appointment. As always if you have comments or questions, we encourage you to let us know.
References
Cryan, J. F., O’Riordan, K. J., Cowan, C. S. M., et al. (2019). The microbiota-gut-brain axis. Physiological Reviews.
Dinan, T. G., Stanton, C., & Cryan, J. F. (2013). Psychobiotics: A novel class of psychotropic. Biological Psychiatry.
Jacka, F. N., O’Neil, A., Opie, R., et al. (2017). A randomized controlled trial of dietary improvement for adults with major depression (SMILES trial). BMC Medicine.
Bloomrd. (n.d.). The microbiome gut-brain axis: What you need to know for brain and gut health. https://www.bloomrd.com/blog/the-microbiome-gut-brain-axis-what-you-need-to-know-for-brain-and-gut-health
Cureus. (n.d.). Gut microbiome and depression: How microbes affect the way we think. https://www.cureus.com/articles/39387-gut-microbiome-and-depression-how-microbes-affect-the-way-we-think
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About Author:
Natalie is a Toronto-based dietitian who who focuses her practice on weight loss support, menopause support, digestive health, heart health and more. Natalie is registered with the College of Dietitians of Ontario.
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