The Gut-Brain Axis: Connection Between Mood and Gut Bugs
Written by Dr. Suzanne Tang
March 14, 2023
Priding myself on my very sturdy gut health, I was surprised to be periodically doubled over with sharp bouts of abdominal pain this past year that would literally stop me in my tracks. Without major changes to my diet, supplements, stress reduction practice or physical activity level, I had a feeling it was due to stress, associated with the business dissolution and starting my practice over. Plus the pain, like clock work, would follow an intensely stressful thought or interaction related to these big changes.
You may relate, perhaps when you feel a “knot” or “butterflies” in your stomach before a presentation or exam. Other times, anxiety can show up as overwhelming waves of nausea or heartburn. How does stress cause such immediate effects on the gut? Does the gut affect how our brain and nervous system handle stress? The answers are “yes” and “yes” and can be explained with the gut-brain axis. The gut-brain axis was briefly mentioned in my last newsletter, “When Your Gut Bugs Go Awry”. Let’s dig deeper on what the gut-brain axis is all about.
The gut-brain axis is the communication network that connects the gut and the brain. This network comprises the vagus nerve, neurotransmitters, gut microbes, and immune system.
The vagus nerve is the longest cranial nerve that connects the gut and the brain and is responsible for the parasympathetic or “rest and digest” response and involuntary actions, such as digestion, breathing, blood pressure, heart rate, coughing and swallowing. It also sends messages back to the brain to help process emotions and triggers the relaxation response to counter the sympathetic stress response or “flight, fight or freeze”. Chronic stress can have detrimental effects to vagal nerve function and can cause numerous disruptive signs and symptoms, including anxiety, depression, dizziness, palpitations, nausea, gas, bloating, abdominal pain, constipation and diarrhea. A human study published in 2014 in the journal of PLoS One found that subjects with irritable bowel syndrome (IBS) and Crohn’s disease had lower vagal tone, more anxiety and depression, and elevated cortisol or stress hormone levels.
The gut and brain also communicate through neurotransmitters, which are produced in the brain and the gut to regulate the stress response. Neurotransmitters, such as acetylcholine, gamma-aminobutyric acid (GABA), and serotonin are produced by bacteria belonging to Lactobacillus, Bifidobacteria, Enterococcus, and Streptococcus species.
About 90% of serotonin is made in the gut and is involved with supporting both brain and gut health. These include:
Elevating mood
Reducing anxiety
Aiding sleep
Improving memory and learning
Regulating intestinal motility
Modulating pain response and vasodilation
Supporting assimilation and absorption of nutrients
Low serotonin levels are linked to insomnia, migraines, anxiety, depression, OCD, PTSD and ADHD, as well as gastrointestinal conditions, such as IBS.
A recent and large human study published in Nature Communications in December 2022 found 13 prevalent strains of bacteria associated with depressive symptoms, suggesting that the gut microbiome plays a very significant role in depression. These bacteria are known to be involved in the synthesis of key neurotransmitters involved with depression, such as glutamate, serotonin and GABA.
Gut microbes also produce other important chemicals, called short-chain fatty acids (SCFA) upon digestion of fiber. SCFA regulate appetite, protect the brain, improve neuroplasticity and support the health of the intestinal barrier as well the blood brain barrier. These barriers act as roadblocks from allowing harmful pathogens, such as viruses, bacteria and parasites and their inflammatory metabolites from passing through to through the blood stream and into the brain.
Dysbiosis or overgrowth of harmful bacteria is a common cause of increased intestinal permeability or leaky gut syndrome. Leaky gut syndrome is associated with IBS, celiac disease, food intolerances and Crohn’s disease but studies also suggest that it may also be correlated with other inflammatory conditions, such as:
Autoimmune conditions, like type 1 diabetes, lupus and multiple sclerosis
Chronic fatigue syndrome
Fibromyalgia
Allergies & asthma
Arthritis
Acne
Anxiety & depression
In particular, lipopolysaccharide (LPS) is an inflammatory toxin made by certain bacteria that easily passes into the bloodstream with leaky gut syndrome. Inflammatory response from the immune system and high LPS in the blood have been associated with a number of neuroinflammatory “leaky brain disorders” including severe depression, anxiety, dementia, Alzheimer’s disease, and schizophrenia.
Understanding the basics of the gut-brain axis provides us with treatment guidelines to address mental health holistically and integratively with psychotherapy and, if needed, drug interventions. In addition, to comprehensive functional stool testing, assessing patients’ neurotransmitter and cortisol levels has been a helpful guide to support mental and emotional wellness with amino acid, herbal and nutrient supplementation.
Eating a whole foods, anti-inflammatory and high fiber diet rich in prebiotics and probiotics are a must. Review my first gut health newsletter, “The Way to Your Health is Through Your Gut” for specific dietary recommendations. A consistent self-care routine that encompasses breath work, yoga, meditation, physical activity, social and nature connection, bodywork, and acupuncture improves neurotransmitter balance and vagal tone. Check out my February Self-Care Challenge on my blog for more ideas. Need more vagal nerve stimulation? Try gargling, singing, chewing your food thoroughly, laughing or splashing cold water on your face.
Finally, we can’t discuss supporting the gut-brain axis without mentioning probiotic supplementation. Clinical trials have shown the multitude of benefits of probiotics, particularly Lactobacillus and Bifidobacteria species for gut, cardiovascular, immune and mental health. Specific strains of Lactobacillus; rhamnosus, casei and plantarum were found to be reduce symptoms anxiety, stress, depression in these clinical trials. A small, randomized controlled study published in 2022 in Translational Psychiatry found that probiotics decreased symptoms of depression and supported gut microbial diversity. More studies like this are in the pipeline to clearly identify the mechanisms of “psychobiotics” or probiotics to specifically address mental illnesses. For more support on optimizing the health of your gut-brain axis, please schedule an appointment with me at OC Whole Family Wellness or Magnolia Wellness.
Hungry for more information on gut health? Look out for my final gut health newsletter next week. And if you are curious, I haven’t had a bout of stress-induced excruciating abdominal pain in awhile. Here’s to a healthy gut-brain axis for all of us!
Yours in Wellness,
Dr. Suzanne Tang, ND, LAc
