How bacteria can improve your mental health as well as your gut health
The human gut is a reservoir to trillions of microbes that influence the development and regulation of digestion and host immunity through homeostasis. This is possible due to bidirectional communication between the gut microbes and the central nervous system (CNS) along the gut-brain axis (GBA). Examples of how the microbiota can signal to the GBA involve the production of neurotransmitters and modulation of ion channels that affect the integrity of the intestinal barrier, whilst the brain can alter the mucosal production and immune function within the gut -consequently affecting the levels of microbial populations. It is important to note that the intestinal barrier helps to prevent external bacteria from invading.
It has been established that your diet will also have a part to play in this composition, incorporating prebiotics (dietary fibres) provide nutrients for existing bacteria to further colonise and probiotics containing live bacteria (usually fermented foods like yogurt and kefir) to enrich the gut with a diverse flora. By doing so this can prevent the chances of dysbiosis occurring which refers to an imbalance in the ecosystem, this can happen as a result of opportunistic bacteria that enter from other sites and compete with the current bacteria for colonisation and nutrients. This event can lead to inflammation that can be a predisposition to mental illnesses such as depression, schizophrenia and anxiety.
The application of probiotics have been associated with alleviating symptoms to a certain extent, the microorganisms interact with the GBA through the regulation and production of neurotransmitters in intestinal epithelial cells. To demonstrate, a study elucidated that treating mice with Lactobacillus spp. resulted in the production of the inhibitory neurotransmitter Gamma-aminobutyric acid (GABA), this can suppress the release of signals or hormones like cortisol responsible for the stress response. Overall this had a positive impact by ameliorating levels of stress associated with anxiety, as well as lowering the depressive score of the experimental group compared to that of the control. Moreover, there is reason to believe that some probiotics have been found to possess some antidepressant-like properties by acting in a similar manner to Selective Serotonin Reuptake Inhibitors. Emerging evidence has shown that the gut microbiome impacts the bioavailability of the amino acid, Tryptophan, through catabolism and metabolism; Tryptophan is the main precursor of serotonin that can cross the blood brain barrier, where it will gain access to circulate the CNS. However, further study is needed to gain better clarity into which bacteria are most salient for developing potential adjunctive therapeutics with antidepressants.
In addition, the anti-inflammatory properties of probiotics are also favourable to the gut and mental health of the host by dampening the effects of pro-inflammatory cytokines. This significantly lowers the chances of dysbiosis and thus, prevents the development of diseases like Pseudomembranous colitis, Irritable Bowel Syndrome (IBS) and Ulcerative Colitis, as well as any long-term complications that the prolonged use of antibiotics can cause. It is difficult to say whether dysbiosis is the major cause for IBS, or whether the inflammation from the development of IBS predisposes the patient to dysbiosis. Nonetheless, antibiotic therapy and IBS destroys most of the resident gut microorganisms leaving an environment favourable for Clostridium difficile to invade and grow out of control. Invading colonies of C. difficile are notorious for eliciting the flare ups that patients experience following the potent exposure to Toxins A and B that enter and kill colonic cells through a cascade of mechanisms, rendering the intestinal barrier impaired. A characteristic of IBS patients is the increased permeability of the barrier which allow immune cells and pro-inflammatory cytokines be recruited and further exacerbate the damage. One of the most promising treatments for relapsing patients is Fecal Microbiota Transplantation (FMT) with success rates of up to 90%, compared to the 30% with oral vancomycin prescription. The principle behind FMT is to restore the bacterial environment of the patient by introducing a fecal sample from an individual with a healthy microbiome. The stool is mixed with saline solution and filtered prior treatment where it will be passed into the patient through colonoscopy, by mouth (in capsule form), enema, nasogastric or nasojejunal tubes. Despite the high success rate, this is not the primary treatment because there are risks that should be taken into consideration, such as the potential to transfer strains of bacteria that are antibiotic resistant, inadvertently worsening the damage.
Upon recognition of the integral role of the gut microbiome in homeostasis and pathogenesis, scientists are striving to expand on pre-existing knowledge and understanding the mechanisms behind GBA interactions between different strains of bacteria. With the hope that this will contribute to the development of novel therapeutics. Nonetheless, this breakthrough has made a significant impact on the health industry by highlighting the importance between the microbiota and diet and nutrition, along with the series of successes following FMT.
