The gut brain axis refers to a communication pathway between the gut and the brain. More specifically, it refers to the communication between the central nervous system and the enteric nervous system—the network of neurons that controls the digestive system. This complex communication network not only ensures the proper functioning of our digestive system, but plays a crucial role in maintaining our mental health.
Research has shed light on how our gut bacteria and microbiota affect many things from our stress response to our mood, revealing the intricate ways in which our digestive health influences our brain function and, conversely, how our brain impacts our gut health. The implications of this relationship are vast, influencing not just our mental health, with ties to anxiety, depression, and mood disorders, but our cognitive function and inflammation processes as well. This post will review a deeper understanding of the gut brain axis, how it is related to both physical and mental health, and how exercise is intimately connected to the gut brain axis.
**This is not medical advice. Please consult your medical provider for more information.
Understanding the Biology of the Gut Brain Axis
The complex interplay between your gut and brain, often referred to as the gut brain axis, helps to maintain both your mental and physical wellbeing. Exactly how does this work?
Your brain is part of the central nervous system (CNS). The gut, or digestive system, is controlled by the enteric nervous system (ENS), which is a part of the peripheral nervous system (PNS). The ENS is often referred to as “the second brain” as it is the largest division of the PNS and contains up to 600 million neurons. Despite it’s connection to the CNS via the vagus nerve (as well as other portions of the spinal cord), the ENS has been shown to act independently of the CNS.
Even though the enteric nervous system has been shown to act on it’s own, there is still bidirectional communication between it and the central nervous system. Research has found links between poor gut health and its affect on mood disorders and vice versa. This pathway allows your digestive system to exert a surprising level of influence over brain function, including mood regulation and cognitive processes. Neurotransmitters, such as serotonin, significantly impacts our stress response and overall mood. A significant portion of neurotransmitters are produced in the gut and is influenced by the gut microbiota. Thus, maintaining a balance in your gut flora is essential for supporting your mental health.
And as of recently, research is also showing a connection to exercise and the gut microbiome. More on this later.
The Role of the Gut Microbiota
What exactly is the gut microbiota? There are microorganisms that colonize on your skin, in your GI and respiratory tract, and other areas. These microorganisms include bacteria, fungi, viruses, and more. Together, the collection of all of these microorganisms living within the GI tract create the gut microbiome.
Based on research in recent years, the understand of the gut brain axis is beginning to shift into a different perspective. This new perspective takes a more systemic approach and is now becoming known as the microbiota-gut-brain (MGB) axis. This differs from the more traditional approach by including the communicating pathways between neural, endocrine, and immune pathways.
Newer research is just now starting to uncover the gut’s role in the development of many different diseases, including but not limited to, cardiovascular disease, mood disorders, and type II diabetes via intestinal inflammation.
Our diets largely enhance our gut microbiota. Diets rich in prebiotics, probiotics, and fiber help enhance the good bacteria within the gut. Whereas diets with low fiber and highly processed sugars negatively influence the composition of the gut microbiome. These negative influences support the development of inflammatory diseases.
Moreover, due to the connection between the gut and the brain, altering the gut microbiota in a positive way has been found to improve symptoms of cognitive disorders like depression and anxiety. Conversely, treating neural and cognitive disorders with selective serotonin uptake inhibitors (SSRIs) has been shown to improve GI function1.
Thus, gut bacteria are pivotal in maintaining both cognitive and GI function. Ensuring the health of your gut microbiota through diet changes can support brain health and enhance your mood, showing just how interconnected the gut brain axis really is.
Dietary Influence
The foods you consume can significantly impact the health of your gut flora. Ingesting a rich blend of prebiotics and probiotics helps nourish your gut flora. The prebiotics feed good bacteria in your gut, whereas the probiotics are live microorganisms that add to the already living population in your digestive tract. Fiber is also important as it is a type of carbohydrate that is not digestible by the body. It helps regulate bloody sugar, stabilizes hunger, and keeps our bowel movements regular.
Moreover, dietary fiber acts as the fuel for beneficial bacteria in your gut, enabling their growth and facilitating their role in serotonin production. This is the same neurotransmitter that modulates mood, appetite, and sleep within your brain. There is a substantial amount produced in the gut, reinforcing the critical relationship between what you eat and how you feel, both mentally and physically. By prioritizing gut health through your diet, you’re actively strengthening your brain’s ability to manage emotions, proving that a thoughtful approach to eating can translate into a profound influence on both mood and cognitive function.
Exercise Influences Both Gut and Brain Health
It has been found time and time again that physical activity and exercise positively improves mood and cognitive disorders. There are chemicals, otherwise known as neurotransmitters, that are released in the brain when we exercise. These neurotransmitters are:
- dopamine: for motivation and attention; the “reward” neurotransmitter
- serotonin: for mood boosting
- noradrenaline: for alertness, focus, and memory retrieval
When we exercise, these neurotransmitters are released to help boost mood, increase energy levels, increase focus and productivity, and reduce stress. Consistent exercise has been shown to positively improve sleep patterns, self-esteem, and many other aspects of mental health.
Exercise was also found to positively impact the gut microflora. Exercise increases anti-inflammatory cytokines, which leads to a decrease in pro-inflammatory cytokines. This can reduce the overall inflammation within the gut, thus reducing the risk of many inflammatory diseases.
With the connection between the gut and the brain, these positive influences on the gut and brain through physical exercise can indirectly improve one another. What I mean by this is that exercise has a positive impact on the brain through boosting mood and reducing stress. Through the gut-brain connection, this improvement seen in the brain can then positively impact the gut and vice versa.
The Impact of Gut Dysbiosis on Mental Health
As newer research comes out, mood disorders are showing an increase in connections with the gut and it’s microbiota. Mental health conditions like anxiety and depression are showing links to poor gut health. Even research on Alzheimer’s disease is beginning to show correlations with gut health.
An imbalance in gut flora (known as dysbiosis of the gut), spurred by dietary choices, stress, and/or antibiotics, can lead to elevated levels of inflammation. Surprisingly enough, high levels of inflammatory markers within the gut are linked to an increase in mood and cognitive disorders. Research is beginning to find some of the roots of our mental wellbeing and its link to gut inflammation.
Signs of an Unhealthy Gut Brain Axis
Recognizing the signals that something could be “off” with your gut brain axis can be your first step towards rebalancing this crucial connection. Here are a few options to consider (remember, this is not an exhaustive list):
- Feeling “off”: It might start with mood changes or a persistent sense of anxiety and depression that doesn’t quite match your life’s circumstances.
- Difficulty with cognition: Trouble concentrating, memory lapses, or brain fog can all point to an upset in your gut flora.
- Disrupted digestive health: Perhaps the most direct indicator, issues like bloating, gas, constipation, or diarrhea can all signal an imbalance in your gut bacteria.
- Overwhelming fatigue: A constant lack of energy, even after a good night’s sleep, can be tied to poor gut health influencing your serotonin production.
- Increased stress response: If you find your stress levels peaking with no apparent reason for setting it off, it might be something to look into.
- Inflammatory reactions: Unexpected inflammation or flare-ups in your immune system can also be a symptom of a disrupted gut-brain connection.
These symptoms are your body’s way of waving a flag as a warning. It’s urging you to pay attention, and possibly, take action.
How Do I Improve My Gut-Brain Axis?
Diet is probably the most important factor when trying to maintain a health gut brain axis. First and foremost, think about having a balanced diet. This includes meats and fishes from sustainable sources (if this is part of your diet), fruits, vegetables, and whole grains. Fruits, vegetables, and whole grains all have decent sources of fiber, depending on which choices you make. Consider supplementing with prebiotics and probiotics if you need a little extra help with digestive issues. This can include bloating, gas, and constipation. Sometimes, the body needs a little supplemental help from time to time. If you happen to be taking antibiotics or have taken them recently, always supplement with probiotics. Antibiotics tend to disrupt the gut microflora.
While dietary choices will have the biggest impact on the gut brain axis, managing your mental health and stress is going to be a close second. If you have a pretty good diet, but you deal with chronic stress, this can still harm the body over lengths of time. Periods of stress in life is necessary and normal. But chronic stress that is not manageable will do more harm than good. Stress can lead to higher levels of inflammation within the body. Techniques such as mindfulness, yoga, and regular exercise can modulate the stress response. This will help keep the harmful effects of stress at bay.
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The Vital Connection Between Exercise and the Gut Brain Axis
Managing chronic stress is something that needs to be taken care of in order to improve the gut brain axis. Managing stress is easier said than done. Balancing work and life (what even is balance, btw… a topic of discussion for another time), getting enough sleep, eating “right,” and keeping up with an exercise routine sometimes feels like way too much.
Here is the important thing to think about—because the gut brain axis involves muscle as well, and there is two-way communication between them all, working on one piece of the puzzle should, in theory, help with another!
We’ve all heard it before…exercise helps control stress levels. For some, the gym is their safe haven after work. A good run can help clear your mind. Start managing your stress simply by working out. But there is more that comes from this.
Regular exercise also helps curb appetite and manages blood sugar levels. With more stable blood sugar levels, your body doesn’t go into periods of craving. Hunger and satiety cues become more regular in nature. Exercise has also been shown to positively influence the gut microbiota. In one study, athletes were shown to have a greater diversity of gut microflora compared to non-active individuals. An abundance in diverse microflora helps aid in digestion and also improves the function of your immune system. As your gut begins to function more efficiently, this in turn improves memory, cognitive functioning, and stabilizes your mood. And due to this two-way communication, the improvement in the brain also encourages improvement in GI function.
Understanding the connection between physical activity and the gut brain axis is not just about preventing or managing health issues. It’s about actively promoting optimal health and wellbeing. By embracing the power of exercise, we unlock a holistic approach to wellness that harmonizes the mind and body. It empowers us to make informed choices for a healthier future.
References
1 Dalton A, Mermier C, Zuhl M. Exercise influence on the microbiome-gut-brain axis. Gut Microbes. 2019;10(5):555-568. doi:10.1080/19490976.2018.1562268
2 Fleming MA 2nd, Ehsan L, Moore SR, Levin DE. The Enteric Nervous System and Its Emerging Role as a Therapeutic Target. Gastroenterol Res Pract. 2020;2020:8024171. Published 2020 Sep 8. doi:10.1155/2020/8024171
3 Piao Kang, Alan Zi-Xuan Wang, Microbiota–gut–brain axis: the mediator of exercise and brain health, Psychoradiology, Volume 4, 2024, kkae007, https://doi.org/10.1093/psyrad/kkae007
4 Schlegel P, Novotny M, Klimova B, Valis M. “Muscle-Gut-Brain Axis”: Can Physical Activity Help Patients with Alzheimer’s Disease Due to Microbiome Modulation?. J Alzheimers Dis. 2019;71(3):861-878. doi:10.3233/JAD-190460
TL;DR
The gut brain axis refers to a communication pathway between the gut and the brain. Research has shed light on how our gut bacteria and microbiota affect many things from our stress response to our mood. It reveals the intricate ways in which our digestive health influences our brain function and vice versa. Exercise is also a vital component between these two, now sometimes referred to as the “muscle-gut-brain” axis. This post reviews the deeper connection between the gut brain axis and exercise.
Tera Sandona is a licensed Doctor of Physical Therapy (DPT) and the founder of PT Complete. She helps high-achieving women break out of cycles of chronic pain, stress, and burnout through her Regulate and Rebuild Method, a sequenced approach that addresses the nervous system first and builds strength second. Her work focuses on helping women finally understand their bodies, rebuild strength, and create lasting resilience that fits real life.
