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Connecting the Dots Between the Nervous System and Digestive Health

The phrase “fight or flight” is thrown around a lot in the world of nutrition, wellness and alternative medicine. It’s often looked upon negatively, as something we need to reduce,  in order to be in a state referred to as “rest and digest” 

Fight or flight is the common term used to describe the sympathetic nervous system, whereas rest and digest refers to the activation of the parasympathetic nervous system. Both the sympathetic and parasympathetic nervous systems are branches of the autonomic nervous system.

The sympathetic nervous system is needed for motivation, alertness and safety while the parasympathetic nervous is most well known for its role in calming the mind and body and its implications in digestive health. While these two branches of the ANS work on opposite ends of the spectrum, they need to work in tandem to set the stage for optimal health. 

Due to lifestyle factors and the level of stress experienced individually and collectively, we see a stronger activation of the sympathetic nervous system, which is not being balanced by parasympathetic activation. 

This has systemic implications, resulting in immune system suppression and hormonal imbalances. These can lead to increased risk of chronic illness and changes to menstrual cycles in females. The activation of the stress response also affects digestion, and long term exposure to stressful situations can lead to digestive conditions. When explaining this to clients, we like to use phrases to describe rest and digest such as “relaxation and proper food breakdown” and “calming and regular elimination” to paint a more comprehensive picture of the importance of this in digestive health. 

So, how does the state of the nervous system (relaxed or stressed) impact the digestive system? 

Picture yourself about to step onto a stage in front of hundreds of people to give a presentation. Unless you are a professional speaker and you encounter this every day, your body will have the same response as if you were being chased by a bear. 

  • Your pupils dilate 

  • You stop salivating 

  • Blood is shunted to the extremities 

  • Bronchi relax

  • Your heart rate increases

  • Glucose is released 

  • Adrenaline is produced 

  • Digestion slows down

  • Your bladder relaxes 

While we may be able to mentally process that we are not in true danger when we stand up to speak, our bodies cannot differentiate between being chased by a bear, giving a presentation, or being stressed from relationships, work, or family. To the body, all stress is cumulative.  If this is an everyday occurrence, the ability to dip into a parasympathetic state becomes compromised.

So, how does sympathetic activation hinder digestion? 

  • The cessation of saliva production inhibits carbohydrate breakdown, as less salivary amylase is present.

  • Blood shunted to the extremities means the normal blood supply to the GI tract is limited, which in turn decreases oxygen delivery, and digestion uses a lot of oxygen!

  • Adrenaline relaxes the muscles of the stomach and intestines, while constricting blood vessels to slow or stop digestion.

  •  The body interprets adrenaline as a signal to run from potential death. It’s presence means things that long term projects that wouldn’t make a difference to your immediate survival, such as digestion, are “turned off” 

  • Stomach acid and digestive enzyme production slows down

To translate this clinically, nutrient availability is decreased in this state, because food is not broken down properly due to a lack of HCL, enzymes, O2 availability and blood flow. This leads to compromised nutrient absorption and the assimilation of nutrients once in the bloodstream is less effective. 

When information is shared about how to activate the parasympathetic system in relation to digestion it’s often recommended to: 

  • Sit down to eat meals without distractions – TV, phone, computer

  • Chew every single bite of food slowly

  • Eat mindfully, not on the go 

.. and these are great tools which should always be implemented. However, to go beyond this, we can say that the health of the individual is determined by their ability to switch effectively between a sympathetic and parasympathetic state. 

For example, you should be able to work under pressure to hit a deadline, have an important meeting, give a presentation or participate in any activity that heightens this “fight or flight” response and then through homeostatic mechanisms return to a parasympathetic state to eat lunch half an hour later. 

The body becomes more or less resilient in response to regular activities and habits. Exercise, for example, teaches the body how to enter a sympathetic state and then regress to a parasympathetic state efficiently and timely. Regular, well thought out exercise exposure that pushes us into a sympathetic state allows us to adjust our allostatic load in a healthy way, to the point of adaptation.

Because the sympathetic nervous system is overactivated in modern society, we see many recommendations to implement practices in daily life that activate the parasympathetic state. This can be part of a well planned whole body routine, that aims to see a relatively seamless flow between the two nervous systems, training the system to be balanced and allowing the body to determine which system to favor in certain situations. 

We recommend the following: 

  • Practice various forms of meditation

  • Spend more time connecting to nature 

  • Get regular massages 

  • Attend yoga classes 

  • Decrease caffeine consumption

  • Organize & Prioritize - Make a list of tasks to be completed in order or priority 

  • Get chiropractic adjustments 

The balance between the sympathetic and parasympathetic nervous systems is imperative to whole body health and healing. It’s a beautiful example of how practitioners from various disciplines can influence digestion and therefore the overall health of an individual. This is a great reason why an interdisciplinary approach to health care is beneficial. 

We encourage you to have the conversation with your patients/clients on the importance of the parasympathetic system in digestion and overall health so they can see how your services benefit them in ways they might not have considered. For all our nutritionists out there, we also encourage you to have a network of like minded practitioners such as chiropractors and RMTs to refer clients to, and to aid in educating clients on the importance of body work for supporting the nervous system. 

Whatever your clients busy lives bring, or the demands they face, challenge them to incorporate one form or practice to help their body tap into its parasympathetic state. Encourage them to watch and observe how small changes can lead to big moves for their  digestive system. We promise, they will thank you!


Jenna is a graduate from The Institute of Holistic Nutrition and a Certified Personal Trainer. She has been a part of the nutrition world for 5 years and loves working with individuals one to one. She is runs her business, Balanced Energy Nutrition, with the goal of creating balance in individuals' lives through both science and holistic practices. In her spare time you can find her taking part in functional training practices, and scouting out unique local cafes to find the best latte.

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