Who would’ve thought part of your digestive system could impact your brain? Since that discovery was made, it’s been a trend in recent years to study the connection between the gut and the brain, called the gut-brain axis. As connections between the brain and mental function are continuously being made, there is the potential to employ the gut-brain axis in mental health therapies. But like with any emerging field in medicine, it raises several ethical considerations that need to be worked through.
The human gastrointestinal tract is inhabited by trillions of microorganisms that are collectively known as the gut microbiome. These microorganisms have been found to play a significant role in human function, specifically in brain activity and mental health, through several mechanisms including neurotransmitter production, immune system regulation, and direct communication within the vagus nerve (1). Given this discovery, we can look at mental health disorders through the gut health lens. Conditions like depression and anxiety are being considered from the perspective of the microbiome (2). As a result, there are new approaches to treating these disorders and reducing the burden on the individuals living with them.
One of the more accessible ways of influencing the microbiome is with probiotics, beneficial bacteria that are usually found in fermented products. Researchers have even coined the term “psychobiotics” to represent the probiotics that induce mental health benefits, such as the Bimuno-galacto-oligosaccharides (B-GOS) and Bacteroides fragilis. Psychobiotics work in three ways: psychological effects on emotional processes, systemic effects on glucocorticoid stress response, and effects on neurotransmitters and proteins (3). An initial comprehensive meta-analysis found that probiotic supplementation had a significant reduction in depressive symptoms (4). Another study even found that a specific combination of probiotics reduced anxiety and improved cognitive ability in patients with Alzheimer’s disease (5).
Ethical questions arise when considering whether patients fully understand that probiotics are experimental treatments, not cures. It’s also important to examine if probiotics should then be considered as pharmaceuticals if they’re part of treating medical conditions, addressing the need to regulate how companies advertise their probiotic products so they don’t overstate their benefits.
A much more extreme treatment option is fecal microbiota transplantation (FMT), a procedure consisting of transferring healthy fecal matter from a donor into a recipient to restore a healthy balance to their microbiome. A case study study showed an improvement in treatment-resistant depression in one patient after FMT, an interesting result for potential future studies. Specifically, there was an increase in Firmicutes and Lachnospiraceae counts and a decrease in Bacteroidetes counts, showing how the microbiome was rebuilt in this patient (6). When using FMT, though, one of the main ethical concerns is the screening process for the donor. Because it is part of the microbiome that is being transferred, the vast-reaching effects of the gut-brain axis play a role in determining a donor because there could be unwanted effects that arise from the donor’s biology. The microbiome is also being drastically changed for the recipient through an invasive process, which puts forth the question of how bad a mental health condition must be before FMT becomes an option. Would the recipient still have the same personality and autonomy after such an immense change?
As with any new avenue of scientific exploration, the ethics of using the microbiome need to be considered at every step. But, this field holds promise, and research should continue to be performed in order to find new avenues for treating mental health disorders.
Graphic by Ariha Mehta
Reviewed by Sanjana Anand
References
Cryan, J. F., O'Riordan, K. J., Cowan, C. S. M., Sandhu, K. V., Bastiaanssen, T. F. S., Boehme, M., ... & Dinan, T. G. (2019). The microbiota-gut-brain axis. Physiological Reviews, 99(4), 1877-2013.
Valles-Colomer, M., Falony, G., Darzi, Y., Tigchelaar, E. F., Wang, J., Tito, R. Y., ... & Raes, J. (2019). The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology, 4(4), 623-632.
Sarkar, A., Lehto, S. M., Harty, S., Dinan, T. G., Cryan, J. F., & Burnet, P. W. (2016). Psychobiotics and the manipulation of bacteria–gut–brain signals. Trends in Neurosciences, 39(11), 763-781.
Ng, Q. X., Peters, C., Ho, C. Y. X., Lim, D. Y., & Yeo, W. S. (2018). A meta-analysis of the use of probiotics to alleviate depressive symptoms. Journal of Affective Disorders, 228, 13-19.
Akbari, E., Asemi, Z., Daneshvar Kakhaki, R., Bahmani, F., Kouchaki, E., Tamtaji, O. R., ... & Salami, M. (2016). Effect of probiotic supplementation on cognitive function and metabolic status in Alzheimer's disease: a randomized, double-blind and controlled trial. Frontiers in Aging Neuroscience, 8, 256.
Cai, T., Shi, X., Yuan, L. Z., Tang, D., & Wang, F. (2019). Fecal microbiota transplantation in an elderly patient with mental depression. International Psychogeriatrics, 31(10), 1525-1526.
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