Can Mental Health Be Bio-Hacked Through The Gut-Brain Axis?
The gut has been referred to as the second brain, but it’s not for reasons you might think. There is an emerging science centered around the gut microbiome and its ability to influence mental health and wellness through the gut-brain axis.
What Is The Gut-Brain Axis?
The gut-brain axis connects the central and enteric (intestinal) nervous systems combined with the gastrointestinal tract. The connection between the gut and the brain can be compared to a two-lane highway with communication flowing freely in both directions. Several systems influence the gut-brain axis.
The autonomic nervous system, composed of the sympathetic and parasympathetic branches, affects bodily functions such as blood pressure, digestion, and breathing.
The central nervous system, consisting of the brain and spinal cord, controls voluntary and involuntary movements.
The enteric nervous system in the GI tract influences intestinal mobility, blood flow, and nutrient absorption.
The hypothalamic pituitary adrenal (HPA) axis assists in regulating stress hormones through communication between the hypothalamus, the pituitary gland, and the adrenal gland.
The Gut Microbiome
The gut consists of a delicate microbiome of bacteria, yeast, and viruses. The bacteria in the gut help maintain the health of the intestinal lining, contribute to digestion, and protect against opportunistic pathogens. The composition of the microbiome is unique to each individual. The development of the microbiome is influenced immediately upon birth and can vary depending on whether the delivery was a vaginal birth or c-section. Additionally, the method of feeding, whether by a bottle or breastfed, contributes to variations in the microbiome between individuals. Throughout adulthood, influences such as environmental toxins, diet, and lifestyle contribute to fluctuations in the biome makeup.
Gut Microbiome Functions
The microbiome in the gut is responsible for multiple functions that impact the gut-brain axis. A healthy balance of microorganisms within the gut helps promote proper nutrient metabolism and neurotransmitter regulation and can also help reduce the risk of developing an inflammatory disease. Functions of the gut microbiome include:
Maintaining a healthy gut lining and intestinal barrier.
Influencing sensory nerves that are responsible for intestinal motility and pain signals.
Regulating neurotransmitters through the production of bacterial metabolites.
Aiding neurotransmitter production such as GABA, serotonin, and dopamine.
Gut Dysbiosis
Microorganisms in the gut help form the intestinal barrier and decrease permeability, thus protecting against pathogens. The bacteria in the gut can release enzymes to break down food, which aid in digestion while also regulating the pH of the gut. The gut microbiome also helps modulate the immune system by regulating and producing inflammatory cytokines. However, gut dysbiosis can occur when there is a disruption in the balance and diversity of microorganisms within the gut. This can lead to an overgrowth of pathogenic organisms and a decline in beneficial host-friendly ones. Gut dysbiosis has been linked to GI disorders such as irritable bowel syndrome, inflammatory bowel disease, celiac disease, metabolic disorders, Alzheimer’s and Parkinson’s disease, and even psychiatric and mood disorders.
Influence Of Stress On The Microbiome
Physiologic and psychological stress can alter the balance of microorganisms within the microbiome. Stress can activate the hypothalamic pituitary adrenal (HPA) axis, part of the central nervous system. When the HPA axis is stimulated, cortisol is released from the adrenal gland, which can directly affect gut motility, gut secretions, permeability, and digestion. Alterations in the environmental conditions within the intestinal mucosal can also contribute to gut dysbiosis.
Neurotransmitter Dysregulation
The gut microbiome’s ability to assist with producing and regulating neurotransmitters plays an interesting role in anxiety and depression. Anxiety and depression have been associated with the dysregulation of GABA, serotonin, and dopamine levels. For example, serotonin is a neurochemical that positively impacts mood, and serotonin receptors can be found within the gut. Serotonin is primarily produced through the conversion of the essential amino acid tryptophan. Serotonin metabolism can be negatively impacted when gut dysbiosis occurs either through the presence of pathogens or with inflammatory gastrointestinal diseases.
Probiotics And Gut Health
Probiotics are beneficial microorganisms to the host and promote a healthy gut environment. Probiotics are commonly found in yogurt, as well as fermented foods and drinks. They can also be available in both pill and powder form. Probiotics can help regulate cytokine production, decrease inflammatory responses, and improve the intestinal wall cell barrier. Additionally, probiotics can help restore and balance the diversity of microorganisms within the gut microbiome, thus improving gut health. There has been an increased focus on the influence of specific strains of probiotics on gut health due to their ability to influence communication with the brain through the gut-brain axis. Lactobacillus and Bifidobacterium strains help reduce inflammatory cytokines within the gut. Research studies have shown that probiotic supplementation with bacterial strains Bifidobacterium and Lactobacillus, when administered together, can improve anxiety through an inhibitory effect on the HPA axis and by decreasing corticosterone levels.
The Future of Therapeutics for Mental Wellness
The gut microbiome plays an integral role in host health. Maintaining balance and diversity of microorganisms within the gut can help optimize general health and mental wellness outcomes. A healthy gut promotes increased resilience to stress and anxiety. As research on the gut microbiome continues to evolve, promising holistic treatments for supporting mental health and wellness lay on the horizon.
References:
1. AKPINAR O. The gut-brain axis: interactions between microbiota and nervous systems. Journal of Cellular Neuroscience and Oxidative Stress. 2018;10(3):783-783. doi:https://doi.org/10.37212/jcnos.610103
2. Appleton J. The Gut Brain Axis: Influence of Microbiota on Mood and Mental Health. Integr Med (Encinitas). 2018;17(4):28-32. https://pmc.ncbi.nlm.nih.gov/articles/PMC6469458/
3. Chen Y, Xu J, Chen Y. Regulation of neurotransmitters by the gut microbiota and effects on cognition in neurological disorders. Nutrients. 2021;13(6):2099. doi:https://doi.org/10.3390/nu13062099
4. Cleveland Clinic. HPA Axis: The stress response system. Cleveland Clinic. Published 2024. Accessed January 25, 2025. https://my.clevelandclinic.org/health/body/hypothalamic-pituitary-adrenal-hpa-axis
5. Coon E. Overview of the Autonomic Nervous System. Merck Manual Consumer Version. Published July 3, 2023. Accessed January 25, 2025. https://www.merckmanuals.com/home/brain-spinal-cord-and-nerve-disorders/autonomic-nervous-system-disorders/overview-of-the-autonomic-nervous-system
6. Fleming MA, Ehsan L, Moore SR, Levin DE. The Enteric Nervous System and Its Emerging Role as a Therapeutic Target. Gastroenterology Research and Practice. 2020;2020:1-13. doi:https://doi.org/10.1155/2020/8024171
7.Góralczyk-Bińkowska A, Szmajda-Krygier D, Kozłowska E. The Microbiota–Gut–Brain Axis in Psychiatric Disorders. International Journal of Molecular Sciences. 2022;23(19):11245. doi:https://doi.org/10.3390/ijms231911245
8.Rinninella E, Raoul P, Cintoni M, et al. What is the Healthy Gut Microbiota composition? A Changing Ecosystem across age, environment, diet, and Diseases. Microorganisms. 2019;7(1):14. doi:https://doi.org/10.3390/microorganisms7010014
9. Yang Y, Yang L, Wan M, Pan D, Sun G, Yang C. Assessment of optimal combinations of therapeutic probiotics for depression, anxiety, and stress. Psychological Medicine. 2024;54(10):1-15. doi:https://doi.org/10.1017/S0033291724000679