The Gut Brain Axis: Benefits of Probiotics for Stress

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Have you ever wondered where the expressions “gut feeling” or “gut instinct” came from?  Have you ever been incredibly nervous about giving a presentation and experienced “butterflies in your stomach?” It’s almost as if our gut is acting like a second brain. What is it trying to tell us?

Science is teaching us that about our “gut brain connection.” This is possible through a network of nerves (i.e. vagus nerve, enteric nervous system), the immune system, and chemical signaling (i.e. neurotransmitters, neuropeptides, etc.) with the gut microbiome being a key regulator in this gut brain axis. This bidirectional flow of information is allowing us to understand how the gut plays a role in mental health and how stress impacts our gut health. 

Our mental or emotional state can affect the health of the gut and, conversely, an issue stemming from our gastrointestinal tract can affect our mental or emotional state.  The question then becomes: is gastrointestinal distress a product or a cause of an imbalanced psychological state?  The answer is likely both depending on the situation.

For example, in the case of someone with celiac disease, gluten causes damage to their intestinal wall, creating inflammation.  I’ve had many celiac patients over the years who report debilitating depression. Once gluten is completely removed from the diet and the gut starts to heal, the depression usually lifts. In these situations, did the celiac patients experience improvements in their mood because they were experiencing fewer symptoms or did reducing inflammation, healing the gut, and altering the gut microbiome have a direct effect on mood improvement? Again, the answer is likely both.

Gut Brain Connection: How Does the Gut Affect the Brain? 

In a study published in 2016, researchers looked at the effect probiotics had on stress among medical students. For eight weeks prior to exams, 23 students in an experimental group were administered fermented milk that contained probiotics (Lactobacillus casei) and 24 students in the control group were administered non-fermented milk that did not contain any probiotics.

Weekly, the researchers assessed the students with questionnaires about abdominal discomfort and anxiety. In addition, they measured their cortisol levels. At the end of the study, the students consuming fermented probiotic rich milk experienced less abdominal discomfort, less anxiety, and a dampened rise in cortisol levels.  Moreover, those same students also maintained a more diverse and healthier population of gut bacteria. 

This study illustrates the benefits of probiotics on mental health. Altering the gut microbiome via consumption of fermented milk containing Lactobacillus casei had a positive effect on mood by lowering anxiety.  Although this was a smaller study, this is an incredible finding as it points to the importance of a healthy gut microbiome in supporting mental health.    

In a similar double-blinded placebo-controlled trial, subjects took the probiotics Lactobacillus helveticus R0052 and Bifidobacterium longum or placebos for 30 days and psychiatric parameters where evaluated.  At the end of the study, subjects taking the probiotics reported less psychological stress and there was a decrease in urinary free cortisol levels.  Again, this study suggests that the benefits of probiotics include a positive influence on the HPA axis by tempering the stress response.    

The Connection Between Stress and Digestion

On the flip side, what happens to your gut when you are chronically stressed out?  A review article from 2011 revealed that chronic stress alters physiological functions in the GI tract including motility, gastric secretion, barrier function (i.e. intestinal permeability), visceral sensitivity, and blood flow.  Additionally, stress negatively affects the biodiversity of the gut microbiome. When the gut microbiome is less diverse we may be more susceptible to pathogens, and our immune system may not be as tolerant. 

We also know that when we are chronically stressed the sympathetic, or “fight or flight,” branch of our autonomic nervous system is stimulated. The sympathetic nervous system is really designed to keep us alive by making sure our body is primed to react in stressful situations (i.e. running from a bear).  As a result digestion becomes low priority. 

The digestive tract functions best when the parasympathetic, or rest and digest, branch of the autonomic nervous system is stimulated as this branch supports saliva production, blood flow, and enzyme release into the gastrointestinal tract.  This is why it’s so important to sit, rest, and be present with your food instead of watching the news or stressing about work. 

Irritable Bowel Syndrome (IBS) and Stress

IBS symptoms can vary in severity from person to person. In general, symptoms of irritable bowel syndrome include:

  • Vague chronic abdominal pain
  • Irregular bowel habits including diarrhea, constipation, or a combination of diarrhea and constipation
  • Heartburn (GERD)
  • Nausea
  • Bloating
  • Flatulence (increased gas)
  • Decreased appetite

It’s well known that many people with IBS also report psychological complaints like anxiety and/or depression.  In fact, it’s been reported that 40-60% of people with IBS suffer from psychological stress. Some studies have shown that those with IBS may experience more visceral hypersensitivity, or an increased pain sensation in and around the internal organs, and stress can worsen this effect. Fortunately, there are ways many ways to help alleviate the symptoms of IBS or eliminate the issue altogether.

How to Maintain and Improve Gut Health

Learning how to improve your gut health is important for all aspects of your overall wellness, including mental health. Here are a few basic tips:

  • Avoid excessive use of antibiotics and ask your doctor if antibiotics are absolutely necessary to treat a particular condition.
  • Eat a whole foods diet rich in fiber and prebiotic foods.
  • Limit processed foods, processed sugar, and antibiotic treated meats.
  • Eat fermented foods as often as you can. This may include sauerkraut, kim chi, beet kvass, kefir, yogurt, miso, kombucha, etc.  Home made is best in my opinion. 
  • Limit your consumption of gluten if you are experiencing symptoms of IBS.
  • Take an assortment of probiotics.
  • Play in the dirt! Go outside with your kids and show them how plants grow in the garden or walk barefoot on the grass or at the beach. 
  • Avoid the use of strong antiseptic chemicals in your home environment or personal hygiene products.



Dr. Drew Sinatra

Meet Dr. Drew Sinatra

Dr. Drew Sinatra is a board-certified naturopathic doctor and self-described “health detective” with a passion for promoting natural healing, wellness, and improving quality of life by addressing the root cause of illness in patients of all ages. His vibrant practice focuses on treating the whole person (mind, body, and spirit) and finding missed connections between symptoms and health issues that are often overlooked by conventional medicine.

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