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How the Gut-Brain Axis Impacts Mental Health & Depression

The Gut-Brain Axis & Depression: A Blog

“All disease begins in the gut,” Hippocrates allegedly claimed some 2500 years ago. According to the latest clinical research, the ancient physician hit the nail on the head.

Growing evidence links an imbalance in the gut microbiota to the pathogenesis of numerous diseases, including IBD, IBS, coeliac disease, type 1 diabetes, autism, metabolic syndrome, cardiovascular disease, and cancer. An imbalance in the gut can also lead to diminished mental health since the gut is connected to the brain through the gut-brain axis.

The gut-brain axis refers to the bidirectional communication between neurons, hormones, metabolism, immune system, the central nervous system (CNS), and gut microbiota. It can affect nearly every aspect of our health, including our psychological well-being.

One study found that patients with mental health conditions like depression are more likely to have gut microbiome dysbiosis, meaning the composition of their gut microbiome is off balance. It works both ways, though. For instance, long-term stress negatively impacts gut-brain communication, causing chronic inflammation and gastrointestinal issues. 

As traditional schools of medicine have been telling us for millennia, the mind and body are absolutely connected. We’re only just beginning to understand how.

What is the Gut Microbiome? 

The human microbiome is made up of trillions of bacteria, viruses, and fungi, the majority of which reside in the gut. Microbiome health and diversity is especially important for the healthy maintenance of nutrition, immunity, and brain function.

We begin developing our microbiome during birth, as we pass through the cervix. This triggers ‘adaptive immunity’, the way our bodies respond to newly introduced microbes. Basically, the microbiome is the immune system in action. 

The more diverse our microbiota, the better our physical and mental health. Low microbial diversity in the gut has been linked to IBD, with diversity levels in patients strongly correlating with disease severity. Patients entering remission often show an increase in their microbial diversity.

Researchers have also found links between the gut microbiome and mood disorders. These findings are especially relevant for IBD patients, who are more prone to anxiety and depression. This is due to a number of factors, mainly the impact of poor gut health on our neurotransmitters and the effects of chronic inflammation. 

Gut Brain Axis

Neurotransmitters and the Gut 

Some 500 million neurons in the gut connect to our brain through the nervous system and the vagus nerve, one of the largest nerves sending signals back and forth between the brain and the gut. These bidirectional lines of communication allow the central nervous system to monitor changes in the gut and respond accordingly to maintain homeostasis.

The brain and gut are also connected through neurotransmitters, many of which are produced by gut cells and the trillions of microbes living there. Studies have linked diseases like IBD with dysregulated neurotransmitter production and activity, and propose this may cause a variety of GI symptoms. It also has a significant impact on mood and cognitive health. 

One of the most important neurotransmitters produced by the gut is serotonin, responsible for mood stabilization and maintaining homeostasis throughout the body. 95% percent of the body’s serotonin actually resides in the gut. It stands to reason that when the gut is off-balance, our mental health will likely take a hit. 

The gut also produces gamma-aminobutyric acid (GABA), a neurotransmitter responsible for blocking certain signals in the nervous system. GABA regulates stress, sleep, fear, and anxiety. When everything is working smoothly, it calms the brain and soothes it before sleep, and protects us from stress and anxiety. Low levels leave us relatively exposed to stress and the negative impacts of stress on the body. 

Last, but certainly not least, is dopamine. 50% of dopamine is produced in the gut. Poor gut health leads to lower dopamine levels, resulting in low motivation, difficulty concentrating, feelings of hopelessness and helplessness, and a loss of pleasure or interest in activities we usually enjoy. Basically, low dopamine levels can result in symptoms associated with depression. 

Thankfully, there are many natural ways to increase serotonin and GABA through herbs and certain foods. See below for more information. 

Inflammation & Depression  

Researchers today consider depression an ‘inflammatory disease’. Patients with inflammatory diseases are more prone to depression, and those with depression show higher markers of inflammation. Depression in IBD patients especially is believed to stem from a dysregulation in the pathways involved in the gut-brain axis, caused and perpetuated by the overproduction of inflammatory cytokines. 

The resulting inflammation leads to heightened sensitivity to stress. The increase in cortisol secretion can cause depressive symptoms. Researchers also observed that cortisol hypersecretion in depressed patients is directly linked to stress experienced by those patients. Depression has also been associated with an increase in oxidative stress, which causes further inflammation, contributing to the progression of the depressive disorder. 

It appears inflammation and depression fuel one another in a vicious cycle. The good news is that the more we understand the relationship between mental health and the gut-brain axis, the closer we are to finding novel and improved solutions for mental health. And there are many ways you can naturally boost your gut and brain health at home.  

How to Increase Microbiome Diversity with Food

For extra gut support, it’s recommended to eat a high-fiber diet, unless you have stricturing Crohn’s or active ulcerative colitis, in which case a low fiber diet is advised. With that in mind, we strongly recommend speaking with your doctor or nutritionist before changing your diet. 

Beneficial foods for gut health & mental health include: 

  • Omega-3 fats found in fish can increase healthy gut bacteria and lowers the risk of brain disorders
  • Probiotic fermented foods like yogurt, sauerkraut, pickles, miso, kimchi, sourdough bread, kefir, and some cheeses contain gut-healthy microbes
  • Polyphenol-rich products like green tea, olive oil, and cocoa contain polyphenols, which can increase healthy gut bacteria
  • Folic acids like spinach, broccoli, asparagus, peanuts, sunflower seeds, fresh fruit, whole grains, liver & seafood.
  • Vitamin B12 like milk, egg yolk, yogurt, salmon, tuna, beef, kidneys, swiss cheese, lamb, clams & herring
  • Vitamin D like oatmeal, orange juice, butter, shrimp, sardines, beef liver, oysters, goat cheese & mushrooms 

For an extra dose of serotonin, try including foods that contain tryptophan, as tryptophan depletion is linked to both depression and anxiety. Tryptophan is an amino acid that can only be obtained through diet and supplements. It’s a mood stabilizer that produces serotonin and melatonin, which help regulate sleep. It also has the added benefit of vitamin B-3, which, amongst other benefits, improves brain function. 

Foods high in tryptophan include:  

  • Eggs 
  • Cheese 
  • Pineapples 
  • Firm Tofu  
  • Salmon 
  • Edamame 
  • Canned Tuna 
  • Nuts & seeds 
  • Turkey Breast 
  • Chicken Breast 
  • Milk 
  • Squash & Pumpkin 
  • Oatmeal 
  • Peanut Butter 


(If you suffer from Crohn’s Disease, ulcerative colitis, or IBS, we recommend discussing your specific dietary needs with your doctor and/or nutritionist.)


Tessa Eskin


Tessa Eskin


This blog is not intended to provide diagnosis, treatment, or medical advice. The content provided is for informational purposes only. Please consult with a physician or healthcare professional regarding any medical or health-related diagnosis or treatment options. The claims made regarding specific products in this blog are not approved to diagnose, treat, cure or prevent disease.

Tessa Eskin


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Tessa Eskin