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Gut Dysbiosis

What is gut dysbiosis and how can it be targeted through probiotic intervention?

The gut or gastrointestinal tract is a long tube that starts at the mouth and ends at the anus. It is within this system that what we eat is processed with nutrients being absorbed and waste being excreted as stool1. The process of digestion can be broken into four main sections, oral processing to mechanically break down food; gastric processing to begin the chemical breakdown; small intestinal processing to allow the absorption of nutrients from macromolecules; then water removal occurs in the colon(1,2)

This digestive process is known to be aided through the action of the gastrointestinal microbiome. The gastrointestinal microbiome is a diverse collection of microorganisms (including bacteria, fungi and viruses), which populates the gut of all mammals(3). Bacteria are the most studied constituent of the microbiome, up to 100 trillion of them are known to exist within the human gut, the majority being located in the cecum of the small intestine with the Bifidobacterium and Lactobacillus families being predominant(4). Exposure to microorganisms within the birth canal means your microbiome begins formation from the moment you are born(5). Furthermore, recent research suggests that the developing baby also comes in contact with these microbes within the womb(6). As a result, the maternal microbiome can impact factors such as obesity risk(7,8,) mental health(9) and immune response(10) within their child.


Alongside inheriting gut flora from our mothers, our microbiome can be modulated through diet. Studies have found that high sugar and processed high fat foods promote harmful bacterial growth(11). On the other hand, foods high in fibre encourage growth of protective bacteria(12).    


Gut dysbiosis is the term for an imbalance between beneficial and harmful strains of bacteria. The result of this occurring can trigger gut hyperpermeability, with decreased selectivity of the gut barrier, allowing passage of unwanted particles(13). This hyperpermeability is often the basis of intolerances or allergies due to small food particles or toxins to passing through the gut barrier and being identified in the blood by the immune system as foreign. Furthermore, gut dysbiosis has also been associated with gas, bloating, diarrhoea and constipation as well as issues such as trouble sleeping, unintentional weight loss or weight gain and more (14,15).

Recent research has investigated the use of probiotics in preventing or treating several health conditions related to the microbiome, where dysbiosis might be involved. Probiotics are defined as “live microorganisms that confer a health benefit to the host when administered in adequate amounts”(16). Probiotics have been observed and studied in fermented foods such as fermented milk products for several years, with the benefits of including them in your diet now becoming clear(17). Studies in recent years have examined the positive impacts seen when probiotics are given in cases of gastrointestinal issues (such as Irritable Bowel Syndrome(18), autoimmune conditions, childhood obesity, and for mental health issues like anxiety and depression.(19) Probiotics are thought to restore the composition of the microbiome and introduce beneficial functions to gut microbiota communities, resulting in the prevention of gut inflammation and other systemic disease phenotypes.

Future advances in our understanding of the importance of the microbiome and the mechanisms by which probiotics can effectively modulate it, may not only help to improve the credibility of probiotic supplementation but also prompt development of novel strategies for treatment or prevention of diseases.




SOURCES

  1.  Helander, H. F. & Fandriks, L. (2014) Surface area of the digestive tract. Scandinavian Journal of Gastroenterology. Vol 49: 6.
  2.  Boland M. Human digestion--a processing perspective. J Sci Food Agric. 2016 May;96(7):2275-83. 
  3.  Barko PC, McMichael MA, Swanson KS. The Gastrointestinal Microbiome: A Review. J Vet Intern Med. 2018 Jan;32(1):9-25
  4.  Integrative HMP (iHMP) Research Network Consortium .The Integrative Human Microbiome Project: dynamic analysis of microbiome-host omics profiles during periods of human health and disease. Cell Host Microbe. 2014 Sep 10;16(3):276-89. 
  5. Bäckhed FRoswall JPeng Y. Dynamics and Stabilization of the Human Gut Microbiome during the First Year of Life. Cell Host Microbe. 2015 May 13;17(5):690-703. 
  6. Aagaard KMa JAntony KM. The placenta harbors a unique microbiome.Sci Transl Med. 2014 May 21;6(237):237
  7. Li Y. Epigenetic Mechanisms Link Maternal Diets and Gut Microbiome to Obesity in the Offspring.Front Genet. 2018 Aug 27;9:342.
  8. Hou YPHe QQOuyang HM. Biomed Res Int. 2017;2017:7585989. Human Gut Microbiota Associated with Obesity in Chinese Children and Adolescents.
  9. Dinan TGCryan JF. The Microbiome-Gut-Brain Axis in Health and Disease.Gastroenterol Clin North Am. 2017 Mar;46(1):77-89. 
  10. Timothy W. Hand. Linking the microbiota, chronic disease and the immune system.Trends Endocrinol Metab. 2016 Dec; 27(12): 831–843.
  11. T. Sen. Diet-driven microbiota dysbiosis is associated with vagal remodelling and obesity. Physiol Behav. 2017 May 1; 173: 305–317.
  12. Jill A. Parnell  Prebiotic fibre modulation of the gut microbiota improves risk factors for obesity and the metabolic syndrome.
  13. Arianna K. DeGruttola,Daren Low,A.Mizoguchi.Current understanding of dysbiosis in disease in human and animal models Inflamm Bowel Dis. 2016 May; 22(5): 1137–1150. 
  14. Exploring the role of gut bacteria in digestion. (2010). . 
    phys.org/news/2010-08-exploring-role-gut-bacteria-digestion.html
  15. Trisha A. Jenkins, Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis. Nutrients 2016 Jan; 8(1): 56. 
  16. Plaza-Díaz J.Adamdec1, Ednrb and Ptgs1/Cox1, inflammation genes upregulated in the intestinal mucosa of obese rats, are downregulated by three probiotic strains.Sci Rep. 2017 May 16; 7(1):1939
  17. Liong MT: Probiotics: Biology, Genetics and Health Aspects. Microbiology Monographs. Heidelberg, Springer, 2011.
  18. Wilkins TSequoia J. Probiotics for Gastrointestinal Conditions: A Summary of the Evidence. Am Fam Physician. 2017 Aug 1;96(3):170-178.
  19. Keren E. Dolan, Probiotics and Disease: A Comprehensive Summary—Part 1, Mental and Neurological Health.Integr Med (Encinitas). 2016 Oct; 15(5): 46–58.