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By Monica Echeverri and E. Dylan Mayer

We all know from personal experience that stress can impact the way we feel. The release of the stress hormone norepinephrine contributes to the familiar bodily responses we experience during moments of acute stress – accelerated heart rate, high blood pressure, and sweating, to name a few. These acute physical responses to stress are typically easy to notice, but the emotional feelings that often accompany chronic stress – irritability, anxiety, worry, and a feeling of being overwhelmed can become chronic if left untreated. Considering the strong link between the gut and the brain, how does stress impact the gut microbiome? And how might contemplative practices like mindfulness-based stress reduction (MBSR) help to counteract these stress-triggered effects?

The Effect of Stress on the Gut Microbiome

A large body of preclinical and clinical research has shown that stress is associated with significant changes in the relative prevalence of gut microbial populations and in the production of microbial metabolites. One consistent findings in both animal and human models has been the reduction in the abundance of lactobacilli and the relative increase in other microbial populations. In some of these studies, stress-induced increases of plasma cortisol levels have been used as a biomarker of the stress response, even though there is little evidence that stress-induced cortisol increases play an important causative role in the modulation of the microbiome.

“These findings suggest that stress can change gut microbial composition by increasing groups of harmful bacteria and reducing groups of beneficial bacteria, and that these gut microbial changes can be transmitted from the mother to her baby.”

In a prospective study, maternal stress and salivary cortisol concentrations during late pregnancy were associated with shifts in the intestinal microbiota of the infants, demonstrating that stress not only is associated with an altered microbiome of the stressed individual (e.g. the mother), but also that these stress-induced changes in the maternal microbiome can be transmitted to the newborn during delivery. Specifically, infants of mothers with high levels of self-reported stress and high cortisol had significantly higher abundances of unhealthy Proteobacterial groups and lower abundances of lactobacilli. These findings suggest that stress can change gut microbial composition by increasing groups of harmful bacteria and reducing groups of beneficial bacteria, and that these gut microbial changes can be transmitted from the mother to her baby.

There are multiple mechanisms that underly the effects of stress and associated autonomic nervous system responses on the gut microbiome. They include stress-induced changes in gut functions that define the habitat in which the gut microbes reside in, and therefore influence the properties of the gut microbial ecosystem. These indirect changes include intestinal permeability (“leakiness”), gut motility, regional transit, and secretion of mucus. In addition, stress-induced increases in norepinephrine have been shown to modulate gene expression of certain gut microbes leading to changes in how the microbes interact with the gut.

The Effect of Meditation on the Stress Response

Meditation is an ancient practice available to everyone. It is well-known to increase calmness, improve awareness, promote happiness, and reduce stress and anxiety. Through various techniques such as mindfulness, focused breathing, and guided imagery, individuals can achieve a state of mental calmness and reduce the physiological effects of stress.

While the direct effects of meditation on the gut microbiome are not yet fully understood, research suggests that there may be specific influences on brain gut microbiome interactions. In a recent study published in the journal General Psychiatry, Sun and collaborators studied gut microbial parameters in 56 Tibetan Buddhist monks and neighboring, non-meditating residents. They found significant differences in the α-diversity of the meditation and control groups, with increased abundances of the bacterial taxa Prevotella and Bacteroides, including the butyrate-producing Faecalibacterium. While this study does not provide evidence for a causal relationship between meditation and gut microbial changes, and didn’t control for other factors, like diet that may have affected the results, it provides suggestive evidence that regular meditation practice can influence gut microbial composition and function in a positive way. Here are a few potential ways in which meditation could impact the gut microbiome:

Meditation has been shown to reduce stress levels, including a reduction of norepinephrine and cortisol plasma levels. As explained above, high stress levels can negatively affect the gut microbiome by altering its composition and reducing the diversity of beneficial bacteria.

Meditation practices such as mindfulness and deep breathing can reduce sympathetic-vagal balance, by reducing the activity of the sympathetic nervous system and activating the parasympathetic nervous system. This change in ANS function is a consequence of shifting the brain into a default mode pattern (active when you are not pursuing a cognitive task or emotional response), a change that is also seen with other relaxation and stress reduction practices.

While several mechanisms can explain how meditation modulates the stress response, one way to evaluate its effects on stress responsiveness is by assessing plasma or salivary cortisol levels. In a recent study, researchers collected salivary cortisol in 40 healthy young undergraduate students before and after completing a meditation course. Although they had a low number of participants, they found that those randomly assigned to the meditation group had lower levels of cortisol after taking the meditation course than before. In another meta-analysis where researchers evaluated academic stress in students, they discovered that meditation treatments moderately affected stress and anxiety. While these findings suggest that meditation can attenuate the stress response, as indexed by a reduction in plasma cortisol, further studies are needed to investigate whether meditation alone can change our gut microbiota.

“…researchers found that cognitive impairment improved and was associated with changes in gut microbiota.”

Other meditation practices such as yoga and mindfulness are also considered as potential therapies for microbiome-related chronic diseases. One study with 123 elderly adults diagnosed with mild cognitive impairment took a mindfulness-based practice that included body scans, walking meditation, and coordination tasks. After examining neuropsychological assessments, inflammatory markers, and gut microbiota profiles for nine months, the researchers found that cognitive impairment improved and was associated with changes in gut microbiota.

Regular meditation practice has been associated with improved sleep quality. Sleep disturbances and insufficient sleep have been linked to changes in the gut microbiome. By promoting better sleep, meditation may indirectly support a healthier gut microbiome.

Some studies have suggested that meditation can positively influence immune function. Since the gut microbiome interacts closely with the-gut associated immune system (which makes up 70% of our total immune system), and plays a vital role in the development and regulation of the immune system, any improvements in immune function through meditation could potentially have an impact on the gut microbiome.

Overall, these findings suggest that stress stimulates the release of certain hormones, in particular the stress hormone norepinephrine, which can modulate the composition and function of the gut microbial ecosystem. Meditation practice, by attenuating the chronic engagement of the stress response may alter brain-gut-microbiome interactions and improve the gut microbial ecosystem. While available evidence is consistent with a positive effect of contemplative practices on reducing stress responsiveness, and with a link between meditation and gut health, more robust evidence to prove that meditation can improve the gut microbiome is needed. Combining lifestyle modification practices with a regular meditative practice is recommended for maintaining good gut health and for improving overall wellbeing.

Monica Echeverri holds a Master of Science in Human Nutrition and Functional Medicine from the University of Western States and currently works as a food photographer, writer, and recipe developer for natural food brands and wellness publications. She has experience in community nutrition education and enjoys spending her time in the kitchen creating healthy recipes that she shares on her Instagram, @mealsbymonica.

E. Dylan Mayer is a graduate from the University of Colorado at Boulder, with a major in Neuroscience and minor in Business. He is currently completing his master’s degree in Human Nutrition from Columbia University. Dylan is fascinated by the close interactions between nutrition, exercise and human health, especially with regard to the brain-gut-microbiome system – and regularly posts his content on his Instagram (@mayerwellness).