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Connecting Digestion and Mood

The Gut-Brain axis is a hot button topic in the world of health. We’ve always known there’s a connection between the gastrointestinal tract and the brainstem, but the research is increasing and beginning to unveil more. Today’s post will be the cliff notes version of some the most recent connections science is explaining.

  • Nervous System – Cranial Nerve X, also known as the Vagus Nerve, starts in the brain and extends all the way to the intestines. It helps to provide movement in the gut and stimulates the “rest-and-digest” part of the nervous system, also known at the parasympathetics. The vagus nerve also sends a message back to the areas of the brain that process emotions. If the gut is stressed, the brain will know about it and visa-versa.

  • The 2nd Brain – did you know that the digestive system consists of 90 million nerve cells? Second only to the nervous system, the gut has the most nerve cells in entire body. This system is called the enteric nervous system – enteric for intestines, nervous system for nerve cells. The intestinal bacteria, aka the microbiome, communicate with these nerve cells to influence neurotransmitters and mood.

  • Stress Response – stress plays a big role in digestive health. Like we talked about with the vagus nerve, emotional and physical stress influence gut motility and digestive secretions. This in turn affects the microbiome and intestinal permeability. This connects the experience of stress to the physical function of the gastrointestinal tract. Stress turns off digestion.

  • Because stress is so prevalent in our culture, I’d like to expand a bit further. Stress triggers production of the stress hormone, cortisol. Cortisol decreases gut motility, decreases GI secretions, and makes the gut “leaky”. With a leaky gut comes imbalance of microflora, called dysbiosis. Dysbiosis leads to symptoms like bloating, stool changes, nausea, reflux, and gas. Changing stress patterns could be a simple fix!

Molecules and Mechanisms

Hold on to your hats! We are going to get a bit more sciencey.

  • Neurotransmitters (NTs) – NTs are chemicals produced by nerve cells in our bodies. These chemicals stimulate changes in hormones, mood, and stress response. Research shows that the microbiome is capable of producing molecules that act as local NTs in the gut. For example, lactobacillus rhamnosus, a type of gut bacteria, stimulates production of GABA, one of the most calming NTs. This is one of many gut bacteria species, which means that the extent of microbiome-mood connection is vast.

  • Tryptophan – you may be familiar with tryptophan as the amino acid in turkey that makes you sleepy. Tryptophan is a precursor to making serotonin. Serotonin is a complex NT that the brain uses to create a feeling of well-being and happiness. Other sources of tryptophan include lentils, eggs, and pumpkin seeds.

Want Evidence?

I’m an evidence person too. Here are a few clinical examples of the connection between the gut and emotions.


Antibiotics are known to disrupt the intestinal microbiome; they are designed to kill off bacteria, and that includes the good kind too. If ever you are prescribed and antibiotic, your doctor has likely informed you the digestive distress is a side effect. Without a a change in microbiome, the mood is affected too.

A study was conducted from 1995-2015 in the United Kingdom, which supported the theory that antibiotics affects mood. The study found that a single use of antibiotics increased the risk for both anxiety and depression. Recurrent use of antibiotics increased that risk even more.


Depression and/or anxiety is shown to occur in more than 50% of people who have Irritable Bowel Syndrome (IBS). Many of these people are prescribed anti-depressants to manage their symptoms, but which came first? The IBS or the mental health symptoms? Research says it’s bidirectional.

Observational studies show that children who experience traumatic life events have an increased risk of IBS as an adult. Studies also show that people with IBS are more prone to mood issues. This may all come down to the microbiome; the pathology of depression may be influenced by unbalanced intestinal flora, leaky gut, immune reactions to endotoxins, and inflammation in the gut. The research continues and more answers are unfolding.

Thanks for geeking out with me. Until next time!

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