Gut Health and Mental Health

We’ve all had days when we don’t feel our best. It’s impossible to be in a good mood all the time, right? Well, mental health issues are a lot more common than you might think. Anxiety is one of the most common mental disorders in the world and more than 350 million people suffer from depression globally [1]. Mental health issues are like onions, they have a lot of layers and gut health is one of them. So, how is gut health linked to mental health? 

Gut-Brain Axis 

The gut-brain axis refers to the two-way relationship between the gastrointestinal tract (also known as the GI tract) and the brain [2]. The GI tract is made up of all the organs within the digestive system, including the gut. Since the GI tract and the brain work together to maintain a healthy balance within the body, gut health has been linked to brain function and mental health. 


How does gut health affect mental health? 


The Gut and Nervous System

The most direct link between the brain and the GI tract is through the vagus nerve. The vagus nerve is the longest of 12 cranial nerves in the human brain. It runs from the brainstem to the colon. The main function of the vagus nerve is to bring in information from internal organs such as the gut to the brain. 

The gut has millions of neurons that make up the enteric nervous system (also known as the ENS). The ENS is described as ‘the second brain’ because it has a similar structure and function as the human brain [3]. The ENS acts as the intestinal barrier in the gut, regulating major processes such as immune response, detecting nutrients, and blood circulation. So, when the gut is altered, the ENS detects the change and notifies the brain through the vagus nerve. The brain then processes the information, resulting in mood changes. 


The Gut and Immune System

The brain and the gut are also connected through the immune system. The gut microbiome has trillions of bacteria, and many of them have a unique structure in the cell wall known as peptidoglycan. Peptidoglycan adds a protective layer to cell walls that activates the immune system through the release of inflammatory cytokines. Cytokines are small proteins that control the growth and activity of other immune cells and blood cells. Cytokines can influence the brain indirectly through nerve pathways or directly through the blood-brain-barrier, a shield that protects the brain from toxic substances in the blood. So, the bacteria in the gut microbiome may influence brain function and behavior through the immune system.

An unbalanced gut microbiome has also been found to influence the availability and regulation of fatty acids and tryptophan. The bacteria in our gut produces short-chain fatty acids like butyrate that have anti-inflammatory properties. These fatty acids have been found to influence energy metabolism which may affect human behavior. Tryptophan is an essential amino acid that is responsible for making chemicals like serotonin also known as the ‘happy hormone.’ Serotonin is made in the gut from tryptophan. So, if the gut is lacking tryptophan, serotonin levels drop affecting mood and behavior. So, an unbalanced gut microbiome may indirectly affect mental health. 


The Gut and Endocrine (hormone) System 

Lastly, the brain and the gut are connected through the endocrine system. Many bacteria in the gut make neurotransmitters and neuropeptides. Neurotransmitters are chemical messengers that transmit signals and neuropeptides are small proteins that are released in the brain to allow neurons to communicate with each other. Since both neurotransmitters and neuropeptides are messengers, gut microbiota imbalances can have an effect on the brain. 

Although the gut-brain axis is real and gut health may help improve your mood, it’s not a solution for mental health issues. Remember, mental health issues are like onions, they have a lot of layers and your gut is only one of them. To learn more about how gut health can affect the human body, check out our Learn page.


Cited sources for more info: 




Written by Kimberly Estrada