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Lachlan Crawford, ND

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Digestion and Mental Health: Is Your Gut Depressed and Anxious?

Updated: Dec 10, 2019


Mood disorders like depression and anxiety can have many physical symptoms that accompany them. Some of the most common symptoms that go along with mental health are changes in the gut. Gut motility, digestion, and appetite changes are tightly paired to stress, anxiety, and low mood. But why is this pairing so common?



The short answer is the gut-brain axis. This is a bi-directional system of communication between the brain and the entire gut system, which includes the digestive organs, the smooth muscle that moves the food along, the immune system, blood circulation, and all the nerves in the gut. It’s so interconnected it’s almost hard to separate the gut from the brain.


There are many methods of communication that relay info in both directions, making gut symptoms flare when mental health symptoms flare. In this article I’ll overview 3 examples of gut-brain communication.


1) Depression and the gut

There are many subtypes of depression, and one well-studied type is low-vitamin D depression. It is commonly seen in seasonal-affective disorder, and in people who don’t make vitamin D very well due to dark skin pigment, low sunlight exposure, or genetic mutations. For whatever reason a person has low vitamin D, it can affect both their mood and their digestive function.


When the body is low in vitamin D, it essentially turns off certain chemical pathways in the brain that help with mood (eg. TPH2 formation of serotonin) while it turns up the same pathways in the gut (eg. TPH1 formation of serotonin). When there is low vitamin D, there is not enough serotonin in the brain, and there is too much in the gut.


This increase in serotonin formation in the gut can lead to loose stools, pain, cramping, bloating, and poor digestion. All while the brain is lacking in serotonin, contributing to you feeling low.


In other words, low vitamin D contributes to low mood, and can cause abdominal cramping, loose stools and poor digestion. This is one of the quickest and easiest underlying causes to investigate when working with depression and gut issues, so be sure to look into vitamin D levels if you’re struggling with this symptom pattern.


Low vitamin D is of course only one reason for low mood and digestive symptoms, so learn more about the causes of depression here.


2) Anxiety and the gut

The second example of gut-brain communication is the classic pairing of anxiety and diarrhea. When some people get stressed, the first thing they notice is that they're running to the bathroom, sometimes even before they register that they’re stressed.


This is because some of the hormones that are produced by the body when you feel anxious directly alter the speed at which your food moves through your gut.


Corticotropin Releasing Hormone, or CRH, is part of the stress hormone cascade. It is released from the brain when you feel psychological or physical stress. There is a useful function to having CRH in the body, but one of its side effects is increasing the motility of the large intestine. That is, it increases movement in the colon, prompting a bowel movement asap.


CRH is necessary for proper alertness (and good things like feeling awake in the morning), but studies show that people with IBS or IBS-like symptoms have a higher intestinal sensitivity to CRH than people who do not have IBS, showing that CRH is a factor in the stress-bowel movement pairing.


The natural way to manage this sensitivity to CRH is by working to reduce stress triggers, and by calming the stress response (aka the HPA axis, or hypothalamic-pituitary-adrenal axis) with diet, adaptogenic herbs, and nutrients.


Again, this is only one of the ways that stress and anxiety can affect the gut, so learn more about anxiety and digestion in my other blog posts.


3) General inflammation and the gut

A third mode of communication between the gut and the brain is via the immune system, through inflammation. What’s interesting is that this can go in either direction:


a) Gut inflammation from inflammatory foods, food sensitivities, and allergies can cause mood symptoms

b) Brain inflammation from stress, brain injury (eg. multiple concussions) and drug use can cause significant changes to digestive function.


Chemical messengers called cytokines are generated when there is local inflammation from one of the causes mentioned above. This is how food sensitivity can be a common cause of a range of mental health conditions, including depression, anxiety, ADHD, and panic attacks. It’s at least in part due to cytokine messengers from the digestive tract traveling to the brain and creating local inflammation and disrupting normal biochemical pathways.



These are three examples of the communication between the digestive tract and the brain, but there are many more bi-directional conversations happening, that all affect both mood and digestion. Other examples are:

  • The brain-calming effect of certain probiotics

  • High fibre intake and the resulting production of short-chain fatty acids that can reduce symptoms of psychiatric conditions

  • The stress hormone cortisol and its negative effect on blood flow to the organs of the digestive tract


From these examples, we can understand the gut-brain connection is an important target when treating mental health. Working with the gut-brain axis involves diet, stress reduction, breathing exercises, lifestyle changes, and sometimes nutraceuticals. Some of these interventions might involve:

  • Reducing the stress response with phosphatidyl serine (PS), L-theanine, GABA, Magnesium, and adaptogenic herbs like ashwaghanda and rhodiola

  • Balancing neurotransmitter function with vitamin D, 5HTP, L-tyrosine, and cofactors B6 and zinc

  • Supporting the microbiome and the immune system with a potent multi-strain probiotic and protective compounds like N-acetyl-glucosamine and glutamine.

  • Eating well for your body by ensuring you’re getting enough fibre, reducing sugar, decreasing exposure to pesticides, and rooting out food sensitivities

  • Decreasing psychological stress with meditation, exercise, sleep, and a mindfulness practice


If you have digestive and mental health symptoms, it is important to address both sides of the gut-brain axis. Learn more with books like The Mind-Gut Connection by Emeran Mayer, MD, and The Psychobiotic Revolution by Scott C. Anderson. Also guide your diet choices for mental health with the help of The Essential Diet by Chris Bjorndal, ND. Schedule a 15-min consult with me here and ask your questions about your mood and digestive symptoms.



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