The HPA Axis: How Your Brain Turns Stress Into Digestive Issues

chronic inflammation gut health hpa axis pituitary gland thyroid vagus nerve May 23, 2023

Have you ever wondered why people with chronic inflammation seem to have endless gut issues? The HPA axis model may explain a large part of the problem.

The Pituitary Gland

Along the HPA axis, your brain and pituitary gland release hormones in response to stress that directly affect digestive function, especially motility and gastric emptying.

The Thyroid

When it comes to IBS and digestive issues, we also need to consider your thyroid. Changes in thyroid function affect more than just our body temperature, metabolism, dry skin and loss of hair and outer eyebrows. One of my first and only thyroid symptoms was chronic constipation no matter how much fiber I ate, water I drank or physical activity I did.

The GI issues caused by thyroid dysfunction, or even subclinical hypothyroidism, are due to reduced motility. Increased thyroid-stimulating hormone (TSH) and decreased circulating levels of T3 and T4 slow digestive processes and decrease bowel transit time. Thyroid issues can also wreak havoc on the gut microbiome. For example, slowed gut motility can let pathogens and opportunistic bacteria hang out for too long and open the door to SIBO.

I run a full thyroid panel on all of my IBS and SIBO patients including TSH, free T3, free T4, reverse T3 and antibodies (anti-TPO and anti-thyroglobulin). It’s rare to see a perfect thyroid panel in the women I see, and even more rare that they have ever had this complete panel run to know where things are going off the rails and whether the dysfunction is the result of autoimmunity. Ask your doctor to order this or I can order it for you at a reduced cash price.

The Vagus Nerve

Outside of hormones, the vagus nerve is a direct line of communication between our brain and gut. Vagus nerve dysfunction caused by chronic stress slows peristalsis, leaving you vulnerable to gut microbiome imbalances, constipation and HPA axis deficiencies. There is an association between vagal nerve dysfunction and traumatic brain injury (TBI) and neurological issues such as Parkinson’s Disease (PD). It would be wise to address the vagus nerve, for example, if someone experiences IBS or SIBO symptoms and has a history of TBI. 

Breaking the Stress Cycle

The vicious cycle created between stress and GI dysfunction needs to be addressed in both systems simultaneously.

In addition to nutrition and supplementation, there are several ways to improve the gut-brain connection:

  • Schedule downtime: Making time for relaxation allows the body to regenerate and helps improve overall well-being. It also allows creativity for new business ideas or new approaches to a problem!

  • Mindful eating: Eating slowly, eating with other people and eating at regular intervals can have a positive impact on your parasympathetic nervous system (“rest and digest”), allowing you to better digest, absorb and assimilate the nutrients you eat.

  • Meditation and deep breathing: Belly breathing, box breathing, and other centering practices are beneficial traditional approaches to relaxation and stress reduction. Check out the book, “Breath: The new science of a lost art” for all the amazing benefits that intentional, proper breathing has.

  • Vagal nerve exercises: Techniques to stimulate the vagus nerve include gargling, singing, laughing, humming, and taking slow, deep breaths. These can be used a few times a day for several months to activate the parasympathetic nervous system and get the gut-brain axis back into communication.

  • Other strategies: Heart rate variability measurements (such as HeartMath), dynamic neural retraining (DNRS), cognitive behavioral therapy and biofeedback are important additional clinical strategies used to help manage the stress response and its effects throughout the body.


To hope, health & happiness, Sara

Function Medicine Clinical Nutritionist, CNS, LDN, FMHC, MS-HNFM



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