The Gut-Brain Axis & Its Major Role in Mental Health

What is the gut microbiome?

The gut microbiome refers to the numerous microbes, viruses, and bacteria that live in your intestines. Did you know there are over 100 trillion bacterial cells in your GI tract? Don’t be too creeped out. You and your gut bacteria have a harmonious relationship… most of the time.

What is the gut-brain axis?

The gut-brain axis refers to the connections between your GI tract, the gut microbiome, and your nervous system.

How do the gut and brain communicate?

There are three main pathways that make up the gut-brain axis – nerves, the neuroendocrine system, and the immune system.

Nerves

Nerves connect to the GI tract and allow communication signals to flow between the gut and the brain.

The vagus nerve acts as the major communication line to the gut and it is affected by movement of your GI tract, as well as the activity of your gut microbes, hormones, and neurotransmitters. Vagus nerve activity has been linked to mood regulation.

The enteric nervous system, which is a network of nerves found throughout the walls of your GI tract, also plays a key role in gut-brain communication.

The bacteria in your gut also make molecules that like short-chain fatty acids, neurotransmitters, and the materials to make them.

Neurotransmitters are chemicals that transfer impulses from nerve fibers. (Examples include serotonin and dopamine.) The activity of certain neurotransmitters affects areas of the brain, which can in turn, affect our mood and behavior.

Neuroendocrine

Your gut microbes also affect the production of hormones involved in the stress response, metabolism, and mood. 

Gut bacteria also make short-chain fatty acids (SCFAs) by breaking down fiber. SCFAs help your body by fighting inflammation. Many mental health disorders have been linked to high levels of inflammation in the body.

Immune

The gut microbiome is an important part of the protective mucus layer within the gut.

Having fewer or less healthy bacteria can lead to a weaker mucus layer in the GI tract, which makes it easier for inflammatory molecules to pass through. This can contribute to higher levels of inflammation throughout the body, including the brain. 

How does gut health affect mental health?

Your gut microbiome is made up of countless species of bacteria. Each species thrives under certain conditions. The composition of your gut microbes can vary based on the foods you eat, your overall lifestyle, stress, and certain drugs.

Researchers are still working to determine what an “ideal” gut microbiome looks like, but we do know that more diverse and rich gut microbiomes are associated with better health outcomes, including a lower risk of depression. 

In fact, the makeup of the gut microbiome can also vary in people with mental health conditions like ADHD, anxiety, and insomnia. Diet changes to manage gut health and/or inflammation (like taking probiotics, including omega-3’s, and eating more fiber) have been linked to symptom improvement in some mental health conditions.

Taken together, these connections give us clues that gut health is strongly connected to mental health.

How to support a healthy gut microbiome for better mental health

Western diets tend to be low in fiber and high in fat, which affects the diversity, richness, and composition of gut microbes, including bacteria that produce helpful molecules like SCFAs and neurotransmitters.

Diets higher in fiber and lower in fat increase helpful bacteria like Lactobacillus and Bifidobacterium, which produce SCFAs that decrease inflammation. This increase in helpful bacteria strengthens the protective layer inside your gut, which decreases permeability and protects your body from inflammation.

Practical Gut Health Tips

1. Include probiotic foods daily. Yogurt, kefir, kimchi, sauerkraut, miso, and tempeh are all great sources of probiotics.
2. Focus on fiber. Keep your gut bacteria happy and nourished by giving them their favorite food - fiber. High-fiber foods include fruits, vegetables, legumes, seeds, and whole grains.
3. Don’t forget fluids. When fiber passes through your intestinal tract, it absorbs water, which can lead to constipation and discomfort if you’re not drinking enough fluids. Set a water goal that works for you and try to sip throughout your day.
4. Exercise matters, too. Being physically active can improve both your mental health and your gut health. Aim to do some form of physical activity each day - anything counts! 
5. Include anti-inflammatory foods. Gut health, inflammation, and mental health are all closely linked. Help your body fight inflammation by including anti-inflammatory foods like walnuts, flaxseeds, chia seeds, salmon, berries, beans, green tea, and a variety of vegetables.

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