Image showing the relationship between the Brain and the Gut

5 min read

The Gut-Brain Axis: The Link Between Your Microbiome and Mental Health

Posted Sep 15, 2021 Updated Mar 15, 2024

The human body has more bacteria than cells. These trillions of bacteria impact many systems, organs, and processes in your body. The balance between the good and the not-so-good bacteria in your microbiome is crucial to your health and well-being. One of the more fascinating ways that bacteria can impact your health is through your gut microbiota, aka the community of bacteria that live in your gut. Did you know that your gut microbiota can communicate with your brain and vice versa? It's true! The composition and diversity of your gut microbiota can impact your mood, cognition, and even conditions like anxiety and depression. Let's dive in to learn more.

What is the Gut-Brain Axis?

The gut-brain axis is a two-way communication system that connects your mental and emotional states with your intestinal functions. In other words, your gut and brain are talking to each other. This connection is why your gut is sometimes called your ‘second brain’. It's also why you might get 'a gut feeling’ or ‘have butterflies’ in anticipation of an event.

But the gut-brain axis is more than just butterflies in your stomach! This connection can have a significant impact on your health. Mounting evidence suggests that a diverse gut microbiota is key to promoting good brain health and overall well-being.1 Researchers are also starting to unravel a potential connection between neurological and neuropsychiatric disorders like stress, autism, depression, Parkinson's, and Alzheimer's, and an imbalance in gut microbiota.2 The negative effects of a hectic lifestyle, characterized by consuming processed foods, enduring stress, antibiotic usage, and pesticide exposure, all contribute to disrupting the delicate balance of your gut microbiota.

Pathways of the Gut-Brain Axis

Now that we know about the gut-brain axis, let's talk about the pathways that make that connection possible: 

The Vagus Nerve Pathway

The gut-brain axis relies on a network of nerves that send signals between the brain and the gut. The primary link between the brain and the gut is your vagus nerve. This powerful nerve helps manage your mood, immune response, and heart rate. It also controls all movement of food through your digestive system, ensuring efficient digestion. The vagus nerve and other various neural pathways also allow for the transmission of sensory information, such as pain or fullness, from the gut to the brain. For example, chemicals in your gut signal to your brain when you're feeling hungry or full. This pathway also passes along the transmission of motor commands from the brain to the gut to regulate digestive processes. In other words, this network of nerves plays a big role in your mood, digestion, and appetite.3 

The Endocrine Pathway

The endocrine system is made of glands that make and regulate hormones. It's also another communication highway connecting the brain and the gut.4 Hormones play a significant role in gut-brain communication. The GI tract produces hormones like serotonin, dopamine, and various gut peptides. These hormones can influence mood, appetite, and other aspects of brain function. For example, serotonin, sometimes called the "feel-good" neurotransmitter, is primarily produced in the gut and can affect mood and emotional well-being. Stress, on the other hand, produces cortisol. This stress hormone impacts the endocrine system resulting in disruptions to your mood and digestion. Cutting-edge research is seeking to better understand how the microbiome can keep cortisol levels from increasing to reduce anxiety and help ease depressive symptoms.

The Immune Pathway

Over 70% of your immune system resides in your gut. The bacteria that live there work diligently responding to toxins, foreign invaders, and pathogens. Stress can also impact the immune system in various ways, including thinning the lining of the gut. This potentially allows ‘bad bacteria’ or toxins through, activating the immune system. These pathogens can also lead to inflammation and gastrointestinal disorders.

Inflammation, Stress, and the Microbiome

Psychological factors, such as stress and emotions, can also impact the gut-brain axis. Stress, for example, can lead to changes in gut motility, gut permeability, and gut microbiota composition, which can affect GI function and overall well-being. The opposite is also true. An imbalance of your gut microbiota could also trigger inflammatory processes that impact your mood.5 So if there's an imbalance in stress hormones and inflammation, you could experience impacts not only on your brain, immune, and digestive health but your mental health as well. 

The Gut-Brain Axis: The Takeaway

The gut-brain axis is a complex and interconnected system that involves neural, hormonal, microbial, and immune signaling between the gut and the brain. It impacts multiple systems that are integral in controlling mood, hormones, and digestive health as well as building a strong immune systemIn other words, it plays a critical role in regulating various aspects of your physical and mental health. As we learn more about the role of the gut microbiome and how it impacts health—it is increasingly clear that maintaining a balanced and healthy gut microbiota is essential to your health and well-being. 


  1. Suganya, K., & Koo, B. S. (2020). Gut-Brain Axis: Role of Gut Microbiota on Neurological Disorders and How Probiotics/Prebiotics Beneficially Modulate Microbial and Immune Pathways to Improve Brain Functions. International journal of molecular sciences, 21(20), 7551.
  2. Kim, N., Yun, M., Oh, Y. J., & Choi, H. J. (2018). Mind-altering with the gut: Modulation of the gut-brain axis with probiotics. Journal of microbiology (Seoul, Korea), 56(3), 172–182.
  3. Breit, S., Kupferberg, A., Rogler, G., & Hasler, G. (2018). Vagus Nerve as Modulator of the Brain-Gut Axis in Psychiatric and Inflammatory Disorders. Frontiers in psychiatry, 9, 44.
  4. Neuman, H., Debelius, J. W., Knight, R., & Koren, O. (2015). Microbial endocrinology: the interplay between the microbiota and the endocrine system. FEMS microbiology reviews, 39(4), 509–521.
  5. Hayley, S., Audet, M. C., & Anisman, H. (2016). Inflammation and the microbiome: implications for depressive disorders. Current opinion in pharmacology, 29, 42–46.
Cheat Sheet
  • The gut-brain axis describes how the gut and the brain interact and talk to and influence each other. That is why your gut is sometimes called your ‘second brain’.
  • The gut-brain axis impacts multiple systems that are integral in controlling mood, hormones, and digestive health as well as building a strong immune system. 
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