Reference Number: 198
There is now an expanding volume of evidence to support the view that commensal organisms within the gut play a role in early programming and later responsivity of the stress system. The gut is inhabited by 1013–1014 micro-organisms, which is ten times the number of cells in the human body and contains 150 times as many genes as our genome. It has long been recognised that gut pathogens such as Escherichia coli, if they enter the gut can activate the HPA. However, animals raised in a germ-free environment show exaggerated HPA responses to psychological stress, which normalises with monocolonisation by certain bacterial species including Bifidobacterium infantis. Moreover, increased evidence suggests that animals treated with probiotics have a blunted HPA response. Stress induces increased permeability of the gut allowing bacteria and bacterial antigens to cross the epithelial barrier and activate a mucosal immune response, which in turn alters the composition of the microbiome and leads to enhanced HPA drive. Increasing data from patients with irritable bowel syndrome and major depression indicate that in these syndromes alteration of the HPA may be induced by increased gut permeability. In the case of irritable bowel syndrome the increased permeability can respond to probiotic therapy. Detailed prospective studies in patients with mood disorders examining the gut microbiota, immune parameters and HPA activity are required to throw further light on this emerging area. It is however clear that the gut microbiota must be taken into account when considering the factors regulating the HPA.
SIGNIFICANCE OF THE STUDY
There is now an expanding volume of evidence to support the view that commensal organisms within the gut play a role in early programming and later responsivity of the stress system. The gut is inhabited by 1013–1014 micro-organisms, which is ten times the number of cells in the human body and contains 150 times as many genes as our genome. It is well established that the brain regulates gut activity but recent attention has focused on the reverse pathway and the manner in which gut microbes can influence the brain. This brain–gut–microbiota axis includes the central nervous system (CNS), the neuroendocrine and neuroimmune systems, the sympathetic and parasympathetic arms of the autonomic nervous system, the enteric nervous system (ENS) and of course the intestinal microbiota. It is becoming clear that alterations in this communication between the gut and brain play a fundamental role in a wide variety of psychological disorders. Moreover, the possibility of regulating the gut microbiota is opening up as a therapeutic target for a host of stress-related disorders. Diet plays an important role in relation to the composition of the microbiota and alterations in diet are known to change the microbial content of the gut. For example, the current review talks about a clinical trial that performed on a population of 30 human subjects, who were classified in low and high anxiety traits. Biological fluids (urine and blood plasma) were collected during 3 test days at the beginning, midway and at the end of a 2 week study. NMR and mass spectroscopy techniques were employed to study global changes in metabolism. Human subjects with higher anxiety traits showed a distinct metabolic profile indicative of a different gut microbial profile and activity. Interestingly, providing probiotics to these subjects over a 2 week period reduced the urinary excretion of both cortisol and catecholamines and partially normalised stress-related differences in energy metabolism and gut microbial activities. The study therefore provides strong evidence that diet can alter gut microbes, which in turn can impact on neurological stress profiles of individuals. There is accumulating evidence that certain probiotics are capable of decreasing the behavioural and endocrine components of stress. However, detailed prospective studies in patients with mood disorders examining the gut microbiota, immune parameters and endocrine activities are required to throw further light on this emerging area.
What we take from this research
What we choose to eat has the potential to alter our gut microbiome, which in turn may help reduce stress levels. This study suggests that probiotics could be especially beneficial for individuals with high anxiety traits.