Main findings
To the best of our knowledge, this is the first study to assess the potential regulation of human gut microbiota by long-term (several years) deep meditation. To minimise the effect of confounding factors, our study strictly matched age, sex, smoking, alcohol consumption and dietary habits between the enrolled monks and control subjects. We observed that the intestinal microbiota composition in the meditation group significantly differed from that of the control group. The control group exhibited higher Chao1, observed-species and Shannon and Simpson indices than the meditation group, indicating the high gut microbial community richness and diversity of the control group. This finding may be related to the sedentary lifestyle of monks (reciting and meditating for long periods each day). ANOSIM and PCoA were used to evaluate the similarity of bacterial communities and to show the significant separation between the meditation and control groups. Altogether, α- and β-diversity indices provided robust evidence that the gut microbiota of the meditation group differed from that of the control subjects.
In this study, we found that several bacterial species differed significantly between the meditation and control groups. At the genus level, Prevotella, Bacteroides, Dialister, Roseburia and Faecalibacterium were predominant in both groups. Prevotella and Bacteroides were found to be significantly enriched in the meditation group. Prevotella was found to be highly abundant in healthy controls compared with that in patients with major depressive disorder.16 17 In addition, the abundance of Prevotella was shown to be significantly reduced in samples of autistic children.18 In a rat food addiction model, the administration of Bacteroides uniformis CECT 7771 was shown to impact the brain reward response, ameliorating binge eating and decreasing anxiety-like behaviour.19 Based on the LEfSe analysis, Megamonas and Faecalibacterium were significantly enriched in the meditation group. Megamanus has been associated with all measured psychocognitive traits.20 In addition, Faecalibacterium was found to be significantly reduced in patients with anxiety disorders compared with healthy controls21 and was associated with a higher quality of life,22 which is consistent with the findings of our study. Collectively, several bacteria enriched in the meditation group were associated with the alleviation of mental illness, suggesting that meditation can influence certain bacteria that may have a role in mental health.
Glycan biosynthesis, metabolism and lipopolysaccharide biosynthesis pathways were enriched in the meditation group. Glycans can reportedly alleviate intestinal inflammation, improve barrier function and reduce infection-induced colitis.23 Studies have shown that the presence of LPS-stimulated Treg cells or exogenous IL-10 significantly promotes IL-10 production by neutrophils and that isoflavone-rich diet anspecifically regulates LPS biosynthesis in the gut microbiota, conferring an anti-inflammatory response and reducing disease severity.24 We have previously reported that inflammatory factors are downregulated in monks practising meditation.6 Furthermore, the meditation group was significantly enriched in toluene degradation and adipocytokine signalling pathways. These findings show the potential effects of meditation on the nervous system through the intestinal flora. Dysregulation of the adipocytokine signalling pathway has been observed in the depression mouse model. In addition, results from human subjects indicate that anxiety and depression can be correlated with adiponectin levels.25 Chronic toluene exposure reportedly increases anxiety in the burying behaviour test of mice, and toluene can reduce neurogenesis and enhance neuronal death.26 The results of plasma biochemical indices further illustrate the impact of meditation on human health. We found that total cholesterol and apolipoprotein B levels were higher in the control group, which decreased immune function and increased the risk of cardiovascular disease.27 These results suggest that meditation may positively impact psychosomatic conditions.
Study limitations
The current study has several limitations. Considering the special environment of high-altitude living and hypoxia, the participating subjects may present with diseases which greatly reduces the enrolment ratio of collected samples. The 16S rRNA sequencing method employed in the present study offers no direct data on functionally important changes in the microbiota. In the future, metagenomic sequencing should be undertaken to examine functional changes in the intestinal microbiota.
Implications
Long-term deep meditation could profoundly impact psychosomatic disorders by altering the structure of the human gut flora. In particular, with the help of a trained therapist, clinicians can provide improved treatment with earlier remission and overall improvements in patients.28 Therefore, the effectiveness of meditation in psychosomatic diseases may be a key research avenue in the coming years.