Emerging research highlights the powerful relationship between our gut microbiota and brain health. This connection, known as the gut-brain axis, refers to the communication network linking our central nervous system and gastrointestinal tract. The gut-brain axis plays a pivotal role in mood regulation and mental well-being, with the gut microbiota having a profound influence on our emotions, thoughts, and even behaviours [1,2].
The Gut-Brain Axis: What Is It?
The gut-brain axis involves bidirectional communication between the brain and gut, primarily facilitated by nerves, hormones, and the immune system [3]. A key player in this communication is the vagus nerve, which acts as a direct line between the gut and brain. Through this network, signals are sent to and from the brain and digestive system, allowing them to influence each other in real time [4].
One of the most fascinating aspects of this system is the role of the gut microbiota—the trillions of microorganisms living in the digestive tract. These microbes contribute to various physiological processes, including digestion, immune function, and even mental health. Research has shown that the composition and balance of gut microbiota can significantly impact mental well-being, potentially influencing conditions like depression, anxiety, and stress-related disorders [5,6].
Gut Microbiota and Mood Regulation.
Studies suggest that the gut microbiota may affect mood by influencing the production of neurotransmitters, the brain’s chemical messengers [7]. For example, serotonin, often referred to as the "feel-good" neurotransmitter, is largely produced in the gut. About 90% of serotonin is made in the gastrointestinal tract, not the brain [8]. This neurotransmitter is essential for regulating mood, sleep, and emotions.
Appleton (2018) highlights that changes in gut microbiota composition can alter neurotransmitter production, potentially contributing to the development of mental health disorders such as depression and anxiety [9]. Specifically, imbalances in beneficial bacteria, known as dysbiosis, have been linked to decreased serotonin production and increased stress response [10].
Additionally, research has found that certain probiotics—live bacteria with beneficial effects on the gut—can positively influence mental health. These probiotics, sometimes referred to as "psychobiotics," may help reduce symptoms of anxiety and depression by supporting a healthy gut environment and enhancing the production of mood-regulating neurotransmitters [11,12].
Gut Inflammation and Mental Health.
Chronic gut inflammation, often resulting from poor diet, stress, or antibiotic use, is another factor that can affect mental health [13]. When the gut is inflamed, the integrity of the intestinal barrier may weaken, allowing harmful substances to leak into the bloodstream. This phenomenon, known as "leaky gut," can trigger systemic inflammation, which has been implicated in several mental health conditions, including depression and anxiety [14,15].
Inflammation can disrupt communication along the gut-brain axis, leading to an overactive stress response and impairing the brain's ability to regulate mood [16]. In fact, many individuals with mental health disorders are found to have elevated markers of inflammation. Reducing gut inflammation through dietary changes, stress management, and probiotics may improve mental health outcomes [17,18].
Diet and Its Role in the Gut-Brain Axis.
The food we eat directly affects the gut microbiota and, by extension, the gut-brain axis. Diets rich in fibre, prebiotics (foods that feed beneficial bacteria), and fermented foods (which contain probiotics) can help maintain a healthy gut microbiota, promoting mental well-being [19,20].
Conversely, diets high in processed foods, sugar, and unhealthy fats can contribute to gut dysbiosis and inflammation, increasing the risk of mood disorders [21]. Research suggests that a Mediterranean diet, rich in fruits, vegetables, whole grains, and healthy fats, supports a healthy gut microbiome and is associated with a reduced risk of depression [22,23].
Improving Mental Health Through the Gut.
While there is still much to learn about the gut-brain axis, the evidence supporting the link between gut health and mental well-being is compelling. Strategies to support a healthy gut microbiota include:
- Eating a balanced diet: Focus on consuming a variety of fibre-rich fruits, vegetables, whole grains, and fermented foods. These nourish beneficial gut bacteria and promote a healthy gut environment [24,25].
- Managing stress: Chronic stress can negatively affect gut health by disrupting the balance of gut bacteria and increasing inflammation [26].
- Using probiotics and prebiotics: Certain strains of probiotics have been shown to reduce symptoms of anxiety and depression [27,28]. Prebiotics, which are fibres that feed healthy gut bacteria, can also support mental well-being by promoting a balanced microbiome.
The gut-brain axis highlights the powerful relationship between our digestive health and mental well-being. By maintaining a balanced gut microbiota through diet, lifestyle changes, and appropriate use of probiotics, it may be possible to support better mental health and reduce the risk of mood disorders. As research into the gut-brain connection continues to grow, understanding and caring for our gut health will remain an essential part of holistic well-being.
References.
1. Mayer EA, Knight R, Mazmanian SK, Cryan JF, Tillisch K. Gut microbes and the brain: paradigm shift in neuroscience. J Neurosci. 2014 Nov 12;34(46):15490-6. doi: 10.1523/JNEUROSCI.3299-14.2014.
2. Cryan JF, Dinan TG. Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nat Rev Neurosci. 2012 Oct;13(10):701-12. doi: 10.1038/nrn3346.
3. Carabotti M, Scirocco A, Maselli MA, Severi C. The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Ann Gastroenterol. 2015 Apr-Jun;28(2):203-209.
4. Bonaz B, Bazin T, Pellissier S. The vagus nerve at the interface of the microbiota-gut-brain axis. Front Neurosci. 2018 Apr 13;12:49. doi: 10.3389/fnins.2018.00049.
5. Fung TC, Olson CA, Hsiao EY. Interactions between the microbiota, immune and nervous systems in health and disease. Nat Neurosci. 2017 Feb;20(2):145-155. doi: 10.1038/nn.4476.
6. Foster JA, Neufeld KA. Gut-brain axis: how the microbiome influences anxiety and depression. Trends Neurosci. 2013 May;36(5):305-12. doi: 10.1016/j.tins.2013.01.005.
7. Sampson TR, Mazmanian SK. Control of brain development, function, and behaviour by the microbiome. Cell Host Microbe. 2015 May 13;17(5):565-76. doi: 10.1016/j.chom.2015.04.011.
8. Yano JM, Yu K, Donaldson GP, Shastri GG, Ann P, Ma L, et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell. 2015 Apr 9;161(2):264-276. doi: 10.1016/j.cell.2015.02.047.
9. Appleton J. The gut-brain axis: influence of microbiota on mood and mental health. Integr Med (Encinitas). 2018 Aug;17(4):28-32. PMID: 31043907; PMCID: PMC6469458.
10. Kelly JR, Borre Y, O'Brien C, Patterson E, El Aidy S, Deane J, et al. Transferring the blues: depression-associated gut microbiota induces neurobehavioural changes in the rat. J Psychiatr Res. 2016 Jan;82:109-118. doi: 10.1016/j.jpsychires.2016.07.019.
11. Dinan TG, Cryan JF. The impact of gut microbiota on brain and behaviour: implications for psychiatry. Curr Opin Clin Nutr Metab Care. 2017 Jan;20(1):49-54. doi: 10.1097/MCO.0000000000000335.
12. Dinan TG, Cryan JF. The impact of gut microbiota on brain and behaviour: implications for psychiatry. Curr Opin Clin Nutr Metab Care. 2015 Nov;18(6):552-8. doi: 10.1097/MCO.0000000000000221. PMID: 26372511.
13. Rea K, Dinan TG, Cryan JF. The microbiome: A key regulator of stress and neuroinflammation. Neurobiol Stress. 2016 Mar 4;4:23-33. doi: 10.1016/j.ynstr.2016.03.001. PMID: 27981187; PMCID: PMC5146205.
14. Maes M, Kubera M, Leunis JC. The gut-brain barrier in major depression: intestinal mucosal dysfunction with an increased translocation of LPS from gram-negative enterobacteria (leaky gut) plays a role in the inflammatory pathophysiology of depression. Neuro Endocrinol Lett. 2008 Feb;29(1):117-24.
15. Cani PD, de Vos WM. Next-generation beneficial microbes: the case of Akkermansia muciniphila. Front Microbiol. 2017 Jul 4;8:1765. doi: 10.3389/fmicb.2017.01765.
16. Wang HX, Wang YP. Gut microbiota-brain axis. Chin Med J (Engl). 2016 Jan 20;129(19):2373-80. doi: 10.4103/0366-6999.190667.
17. Kiecolt-Glaser JK, Wilson SJ, Bailey ML, Andridge R, Peng J, Jaremka LM, et al. Marital distress, depression, and a leaky gut: Translocation of bacterial endotoxin as a pathway to inflammation. Psychoneuroendocrinology. 2018 Jun;98:52-60. doi: 10.1016/j.psyneuen.2018.07.007.
18. Schirmer M, Smeekens SP, Vlamakis H, Jaeger M, Oosting M, Franzosa EA, et al. Linking the human gut microbiome to inflammatory cytokine production capacity. Cell. 2016 Nov 17;167(4):1125-1136.e8. doi: 10.1016/j.cell.2016.10.020.
19. De Filippo C, Cavalieri D, Di Paola M, Ramazzotti M, Poullet JB, Massart S, et al. Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. Proc Natl Acad Sci USA. 2010 Aug 17;107(33):14691-6. doi: 10.1073/pnas.1005963107.
20. Jacka FN, O'Neil A, Opie R, Itsiopoulos C, Cotton S, Mohebbi M, et al. A randomised controlled trial of dietary improvement for adults with major depression (the "SMILES" trial). BMC Med. 2017 Jan 30;15(1):23. doi: 10.1186/s12916-017-0791-y.
21. Lach G, Schellekens H, Dinan TG, Cryan JF. Anxiety, depression, and the microbiome: A role for gut peptides. Neurotherapeutics. 2018 Jan;15(1):36-59. doi: 10.1007/s13311-017-0585-0.
22. Opie RS, O'Neil A, Itsiopoulos C, Jacka FN. The impact of whole-diet interventions on depression and anxiety: A systematic review of randomised controlled trials. Public Health Nutr. 2015 Nov;18(11):2074-93. doi: 10.1017/S1368980014002618.
23. Gómez-Pinilla F. Brain foods: the effects of nutrients on brain function. Nat Rev Neurosci. 2008 Jul;9(7):568-78. doi: 10.1038/nrn2421.
24. Valles-Colomer M, Falony G, Darzi Y, Tigchelaar EF, Wang J, Tito RY, et al. The neuroactive potential of the human gut microbiota in quality of life and depression. Nat Microbiol. 2019 Sep;4(3):623-632. doi: 10.1038/s41564-018-0337-x.
25. Russell WR, Hoyles L, Flint HJ, Dumas ME. Colonic bacterial metabolites and human health. Curr Opin Microbiol. 2013 Jun;16(3):246-54. doi: 10.1016/j.mib.2013.07.002.
26. O'Mahony SM, Clarke G, Borre YE, Dinan TG, Cryan JF. Serotonin, tryptophan metabolism and the brain-gut-microbiome axis. Behav Brain Res. 2015 Jan 15;277:32-48. doi: 10.1016/j.bbr.2014.07.027.
27. Savignac HM, Tramullas M, Kiely B, Dinan TG, Cryan JF. Bifidobacteria modulate cognitive processes in an anxious mouse strain. Behav Brain Res. 2015 May 15;287:59-72. doi: 10.1016/j.bbr.2015.03.067.
28. Wallace CJ, Milev R. The effects of probiotics on depressive symptoms in humans: A systematic review. Ann Gen Psychiatry. 2017 Mar 22;16:14. doi: 10.1186/s12991-017-0138-2.
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