Gut Microbiome: Introduction
The gut microbiome is made up of a host of microorganisms that can be found in the human gastrointestinal tract. These microorganisms, consisting of prokaryotes, viruses, and fungi, facilitate the maintenance of host homeostasis. 1 In maintaining host homeostasis, the gut microbiota contributes to the development and function of the immune, metabolic, and nervous systems.2
As we explore the components and functions of the microbiome, we will delve into the consequences and implications of a disturbance in microbial composition.
Development of the Microbiome
The principal microbiome is formed during the first two years of a person’s life.3 The initial introduction to bacteria is via the maternal microbiota, through contact with amniotic fluid, the placenta, and mode of delivery.4 Infants born via vaginal delivery receive some of their microbiota from the maternal vaginal canal. Those born via cesarean section (c-section) receive their first major exposure to bacteria from both the hospital environment and the normal flora of the mother’s skin.4, 5 As the infant gets older and becomes exposed to various microbes through different feeding methods, the gut microbiome continues to evolve and is subject to change. However, once solid foods become prominent in the child’s diet, around two years old, the gut microbiome begins to stabilize. 4
With the gut microbial species making up approximately 3.3 million genes, it is suggested that the potential effects of these organisms on human health arecoe far greater than anticipated.5
Factors Influencing Gut Microbiome
There are several factors that directly and indirectly affect gut microbial composition. Evidence suggests that the interactions between the diet, immune system, genetics, normal microflora, and extrinsic environment contribute to such compositional changes.6
Diet & Culture
Diet is a vital influential factor that contributes to alteration in gut bacteria makeup.7 Evidence shows that your diet can have both short-term and long-term effects on the ecosystem that exists within the gut.8 For example, studies show that those who employ a plant-based diet have considerably different gut microbiomes than those who consume significant amounts of meat.1 When compared to people who eat a plant-based diet, individuals who consume animal protein have higher levels of some species in their GI tract, such as Bacteroides. Those engaging in plant-based meals, however, have an abundance of Prevotella species in their gut.1,8
While lifestyle can contribute to a person’s dietary choices, their culture plays an essential role as well. It has been observed that those who follow a Western diet consume meals high in saturated fats and sodium. Due to the increased saturated fats and additives commonly found in Western foods, there is a clear correlation between altered microbiota composition and its inflammatory abilities.1
The Mediterranean Diet, on the other hand, has been shown to have anti-inflammatory and general disease prevention properties.10, 13 This diet is rich in antioxidants and includes green leafy vegetables, legumes, fresh fruits, and whole grains. It places a focus on consuming a diet rich in healthy fats from plants and the occasional red wine due to its ability to lower inflammation.10
Through the implementation of dietary changes, microbial diversity and stability can be potential targets for dysbiosis.7
Stress
Stress is the body’s response to anything that requires action or attention. It can manifest in physiological ways, affecting normal GI tract functions including gut motility, secretion, and permeability.11 While stress is normal, if it begins to negatively impact your physical or mental health over time, it can cause health issues like digestive problems and depression.12
Through its impact on gut microbes, stress can have a significant negative impact on health. Stress-related inflammation can lead to the release of pathogenic microorganisms that support dysbiosis and leaky gut epithelium.13 Leaky gut epithelium is characterized by an increase in intestinal permeability, leading to an inflammatory response. The resulting inflammation and associated symptoms can increase the risk for depression, anxiety, and generalized stress.14
Inflammation
Inflammation is an immune response produced by the body after exposure to harmful stimuli, including pathogens and toxins.15 This immune response can lead to the removal of toxic stimuli and initiate the healing process.15 While inflammation can be beneficial, it has its downsides as well. When inflammation becomes uncontrolled, it can become chronic and lead to the emergence of chronic inflammatory disorders. As a result, many chronic diseases, including gastrointestinal disorders, arthritis, and cardiovascular disease, are thought to have inflammation as their common underlying cause.15,16
Effects of Inflammation on the Microbiome
There are numerous studies linking changes in microbial composition with inflammation and metabolic dysfunction.16 The presence of certain bacteria can incite inflammation in various body tissues. The gut typically consists of microorganisms belonging to the Firmicutes and Bacteroides phylum.2,16 However, when a person has irritable bowel disease (IBD), Firmicutes concentrations are depleted, while Proteobacteria are increased.16 Dysbiosis that results from this can have an impact on extraintestinal health in addition to intestinal health. Bloating, stomach pain, food intolerance, and headaches are a few examples of symptoms.14
Immune System: Diabetes
Due to the microbiome’s capacity to promote pathogen colonization resistance and promote the generation of cytokines and T cells, the immune system directly benefits.17 When the microbiome is in a state of dysfunction, it can affect immune response and reduce drug efficiency. It is believed that a lack of microbial variety may be a sign of disease in the case of autoimmune disorders like diabetes or rheumatoid arthritis.15,17
According to studies conducted in Northern Europe, compared to infants without the condition, those with type I diabetes alleles have higher levels of proinflammatory species and a reduced variety of gut microbes.17 When compared to their healthy counterparts, diabetic children also exhibit an increase in Bacteroidetes followed by a decrease in Actinobacteria and Firmicutes.
Sleep
Alterations to the microbiota can impact sleep quality in addition to having an impact on the immune system. While the relationship between the immune system and the gut microbiome continues to be explored, their relationship with sleep remains unclear.18 However, it has been ascertained that the proinflammatory cytokines of the acute phase pathway (IL-1β and IL-6) have a substantial relationship with sleep physiology. Prolonged sleep deprivation raises levels of IL-1β and IL-6, along with persistent stress.18
Conclusion
The microbiome is frequently referred to as the “forgotten organ” 16 because of its central but little-understood role in maintaining physiological processes. As more research continues to be done regarding this organ, we will continue to explore its profound effects on homeostatic balance and the potential targeting of microbial composition in disease treatment and prevention.
References
1 Al Bander Z, Nitert MD, Mousa A, Naderpoor N. The Gut Microbiota and Inflammation: An Overview. Int J Environ Res Public Health. 2020;17(20):7618. Published 2020 Oct 19. doi:10.3390/ijerph17207618
2 Lobionda S, Sittipo P, Kwon HY, Lee YK. The Role of Gut Microbiota in Intestinal Inflammation with Respect to Diet and Extrinsic Stressors. Microorganisms. 2019;7(8):271. Published 2019 Aug 19. doi:10.3390/microorganisms7080271
3 National Institute of Environmental Health Sciences. Microbiome. National Institute of Environmental Health Sciences. Published April 5, 2022. https://www.niehs.nih.gov/health/topics/science/microbiome/index.cfm
4 Mohajeri MH, La Fata G, Steinert RE, Weber P. Relationship between the gut microbiome and brain function. Nutr Rev. 2018;76(7):481-496. doi:10.1093/nutrit/nuy009
5 Stiemsma LT, Michels KB. The Role of the Microbiome in the Developmental Origins of Health and Disease. Pediatrics. 2018;141(4):e20172437. doi:10.1542/peds.2017-2437
6 Belkaid Y, Hand TW. Role of the microbiota in immunity and inflammation. Cell. 2014;157(1):121-141. doi:10.1016/j.cell.2014.03.011
7 Leeming ER, Johnson AJ, Spector TD, Le Roy CI. Effect of Diet on the Gut Microbiota: Rethinking Intervention Duration. Nutrients. 2019;11(12):2862. Published 2019 Nov 22. doi:10.3390/nu11122862
8 Tomova A, Bukovsky I, Rembert E, et al. The Effects of Vegetarian and Vegan Diets on Gut Microbiota. Front Nutr. 2019;6:47. Published 2019 Apr 17. doi:10.3389/fnut.2019.00047
9 Tsigalou C, Konstantinidis T, Paraschaki A, Stavropoulou E, Voidarou C, Bezirtzoglou E. Mediterranean Diet as a Tool to Combat Inflammation and Chronic Diseases. An Overview. Biomedicines. 2020;8(7):201. Published 2020 Jul 8. doi:10.3390/biomedicines8070201
10 Rishor-Olney, C. R., & Hinson, M. R. (2020). Mediterranean Diet. In www.ncbi.nlm.nih.gov. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK557733/
11Konturek PC, Brzozowski T, Konturek SJ. Stress and the gut: pathophysiology, clinical consequences, diagnostic approach and treatment options. J Physiol Pharmacol. 2011;62(6):591-599.
12 National Center for Complementary and Integrative Health. Stress. NCCIH. Published January 2020. https://www.nccih.nih.gov/health/stress
13 Madison A, Kiecolt-Glaser JK. Stress, depression, diet, and the gut microbiota: human-bacteria interactions at the core of psychoneuroimmunology and nutrition. Curr Opin Behav Sci. 2019;28:105-110. doi:10.1016/j.cobeha.2019.01.011
14 Camilleri M. Leaky gut: mechanisms, measurement and clinical implications in humans. Gut. 2019;68(8):1516-1526. doi:10.1136/gutjnl-2019-318427
15 Chen L, Deng H, Cui H, et al. Inflammatory responses and inflammation-associated diseases in organs. Oncotarget. 2017;9(6):7204-7218. Published 2017 Dec 14. doi:10.18632/oncotarget.23208
16 Wang J, Chen WD, Wang YD. The Relationship Between Gut Microbiota and Inflammatory Diseases: The Role of Macrophages. Front Microbiol. 2020;11:1065. Published 2020 Jun 9. doi:10.3389/fmicb.2020.01065
17 Lambring CB, Siraj S, Patel K, Sankpal UT, Mathew S, Basha R. Impact of the Microbiome on the Immune System. Crit Rev Immunol. 2019;39(5):313-328. doi:10.1615/CritRevImmunol.2019033233
18 Smith RP, Easson C, Lyle SM, et al. Gut microbiome diversity is associated with sleep physiology in humans. PLoS One. 2019;14(10):e0222394. Published 2019 Oct 7. doi:10.1371/journal.pone.0222394
Bio
Erysa Gayle is a current Larkin University ’23 student studying for a Master’s in Biomedical Science. She has an interest in attending medical school and further exploring the benefits of a whole-body approach to medicine.
Abstract/Highlight
The species of the gut microbiome make up over 3.3 million genes, and due to its vast diversity, its potential effects on health are far greater than anticipated.
With a person’s diet being one of the most influential factors that contributes to microbial composition, a diet consisting of mainly proteins or plant-based foods can shift the predominating bacterial strains. A shift in bacterial strains, along with increased stress can lead to inflammation, with the potential of chronic disease developing if the inflammation persists.
Since the microbiome is regarded as the “forgotten organ”, further research should continue to explore its effects on homeostasis.
