How Meditation Affects Our Fight-Flight-Freeze and Rest-and-Digest Nervous Systems?

Nowadays, it is rare to meet a person who is not practicing, has not tried, or at least heard of meditation. According to social media and various meditation gurus, it would seem that meditation can solve all of the problems of the modern world: stress, obesity, financial difficulty, insomnia, anxiety and cure various diseases, such as depression or cancer. But at the same time, mindfulness is still considered by many to be a very esoteric practice, associated with shamanism, chakra opening, or some other voodoo pseudoscience practice. Mindfulness is seen as something that is very 'unscientific'.

But what does science and peer-reviewed research articles say about meditation? This is the third article in a series “Science of Meditation” where I describe the science behind meditation on how it affects our brain, body, behavior and health. In the first article we explored what is happening in your brain when you meditate, in the second article we discussed how meditation related changes in the brain translate into our behavior with examples on stress, pain and sadness. This time we will explore how meditation affects the balance between the two sides of our involuntary nervous system – fight-flight-freeze and rest-and-digest – and how that affects our body – our stress hormones, immune system, and our chances to develop cardiovascular and mental disorders.

Fight-flight-freeze or rest-and-digest?

Our nervous system has two main arms – voluntary (somatic) and involuntary (autonomous). The involuntary, or autonomous nervous system is responsible for regulating the body's unconscious actions, and consists of two divisions itself. The first one is known to most of us as fight-flight-freeze (sympathetic), the second one is a much more pleasant sounding one rest-and-digest (parasympathetic, also known as feed-and-breed).

Fight-flight-freeze system primarily kicks in when you experience a threat or are under stress. As a result, stress hormones are released and many other biochemical processes get turned on that basically mobilizes your body to deal with the threat – flee, fight or freeze. Energy is diverted from restorative, healing processes to our muscles, attention is sharpened, heartbeat rises, breath gets shallow and fast. Rest-and-digest, as you might have guessed already, and what its name suggests – is completely opposite to the fight-flight-freeze system. Rest-and-digest system is activated after the threat has passed, when we are relaxed, especially after eating. It stimulates sexual arousal, lowers our blood pressure, promotes digestion, eliminates waste from our bodies, stimulates restorative and rebuilding processes in our cells.

Short-term vs chronic stress

Short term activation of the flight-flight-freeze system is beneficial and actually can be life-saving. That’s actually the main purpose of this system – make us react quickly to a threat to get away or deal with it and thus increase our survival chances. However, nowadays our stressors changed from lions in bushes to constant deadlines, social pressure and never-ending to-do lists. The threat never goes away and thereby the fight-flight-freeze system is chronically active.

Such overactivation of fight-flight-freeze damages multiple aspects of our health and raises the risk of multiple diseases. For instance, chronic stress raises blood pressure and increases levels of artery-clogging deposits, thereby increasing risk of hypertension and other heart and cardiovascular disorders; triggers changes in the brain that increases vulnerability to mental illness, such as depression, anxiety, addiction; dysregulates our metabolism and might contribute to obesity and diabetes.

Meditation turns on our rest-and-digest system

Considering the myriad of harmful effects that chronic stress has on our health, it seems truly a good idea to put in the effort in managing our stress in order to stay healthy. Numerous studies provide evidence that meditation calms down our fight-flight-freeze system, activates our rest-and-digest system and is one of the best ways to reduce stress, in addition to sleep and physical exercise.

One rather surprising way to measure the activation of fight-flight-freeze and rest-and-digest is measuring skin conductance, or put more simply – measure how well our skin transmits electricity. When the fight-flight-freeze system is activated, when we get stressed, we sweat. Salty water, or sweat, is a really good electricity conductor, which in turn increases skin conductance. A 2009 study showed that even short-term meditation reduces skin conductance, indicating increased rest-and-digest activity and reduced fight-flight-freeze activity.

Another rather clear method to evaluate which of the two - fight-flight-freeze or rest-and-digest - is predominant, is simply measuring levels of the stress hormones, such as cortisol, in our blood or saliva. A 2017 meta-analysis found that meditation reduces levels of cortisol, indicating lower levels of stress in people who practice meditation. Another 2021 meta-analysis further showed that meditation is especially effective at reducing stress hormone levels the so-called at-risk population – those with already elevated cortisol levels.

Meditation improved heart health

One of the strongest felt signs of increased stress (meaning activated fight-flight-freeze) is that our heart starts beating hard and fast and our blood pressure goes up. A 2017 meta-analysis that included 45 individual randomized control trials on meditation and cardiovascular health found that meditation reduces blood pressure and heart rate. Importantly, a reduction in heart rate and blood pressure was observed not only in adults but also adolescents and elderly people, both healthy and with higher than-healthy blood pressure (hypertensive).

Another 2018 systematic review and meta-analysis found that even workplace-based mindfulness meditation programs lower stress hormone cortisol and increase measures of heart rate variability, which is a marker of physical health.

In a 2017 Scientific Statement From the American Heart Association, it even says that «…considering the generally low costs and risks associated with meditation, meditation may be considered as a reasonable adjunct to guideline‐directed cardiovascular risk reduction...»

Meditation might have beneficial effects on immune system

Several studies found positive effects of meditation for our immune system health. A 2018 meta-analysis reports that workplace mindfulness-based interventions, such as meditation, are associated with a better response to vaccines, meaning that people who meditate might be better protected after vaccination against pathogens. Moreover, the authors find reduced concentrations of inflammation markers in the mindfulness meditation group, suggesting reduced inflammation level. Another 2014 meta-analysis also found that mind-body therapies reduce markers of inflammation. Importantly, all of these studies are rather small and with varying results. Bigger, better quality and better controlled studies are needed.

Meditation reduces the risk of multiple diseases

As discussed above, chronic activation of the fight-flight-freeze system damages our cells and increases the risk of multiple diseases, including cardiovascular and mental disorders. Accordingly, reduced activation of fight-flight-freeze and increased levels of rest-and-digest, as in the case of meditation, should lower our chances of various disorders.

A recent 2020 study published in The American Journal of Cardiology showed that those who practice meditation have lower risk of cardiovascular diseases, such as hypercholesterolemia (having very high levels of low-density lipoprotein cholesterol in their blood, which is known as "bad" cholesterol because it can build up in the walls of the arteries, making them hard and narrow), stroke and diabetes, even after adjusting for age, gender, body mass index, race, marital status, cigarette smoking, sleeping duration, and depression.

A 2022 meta-analysis concluded that meditation seems to produce significant small-to-moderate reductions of the levels of anxiety, stress (including post-traumatic), and general psychopathology, as well as small but also significant improvements in depression and mental health-related quality of life. Other studies support these findings and show that meditation reduces anxiety and risk of depression. Finally, a 2019 study reported that expert meditators have more preserved brain structures than age-matched non-meditators and that meditation practice may promote healthy aging and delay the onset of dementia.

In this article, we addressed how meditation affects the balance between the two branches of our nervous system: fight-flight-freeze and rest-and-digest. Even though short-term activation of the fight-flight-freeze is vital for our survival, chronically active stress response wreaks havoc on our health. Research clearly shows that meditation reduces the overactivation of the fight-flight-freeze branch of our nervous system and turns up the volume of rest-and-digest which subsequently improves our health and reduces the risk of multiple disorders.