The microbiota our friend for life

What is the microbiota?

The microbiota is the ecosystem of micro – organisms that live in the gut. It is essential for good health and staying healthy.1

The particular balance of micro – organisms living with each person is unique, no two individuals have exactly the same microbiota.1 Maintaining a diverse balance of different species and maintaining the particular microbiota that is right for the individual is essential for healthy functioning.1 If one or several species of micro – organisms becomes over - represented, the microbiota can become unbalanced, resulting in a condition called dysbiosis. This can result in health problems, such as diarrhea, nutritional imbalances and even problems related to immune system dysfunction. A number of illnesses caused by excessive inflammation of the intestine, such as Crohn’s disease, ulcerative colitis, or even irritable bowel syndrome (IBS) are thought to have links to dysfunction of the microbiota.2-6

The microbiota provides protection, immune stimulation and nutrition1,4,7


The microbiota is the body’s first line of defence against invading bacteria. The physical presence of the beneficial bacterial lining in the intestinal walls creates a protective barrier preventing disease – causing bacteria from attaching. The intestinal microbiota also releases anti – bacterial substances, which help to prevent uncontrolled growth of problematic species of bacteria.1,4

Immune stimulation

The microbiota helps to stimulate and develop the immune system, helping the body to defend itself against pathogens and at the same time ensuring that it does not overreact, in a way that may cause chronic or damaging inflammation.4,7


The microbiota is able to produce essential compounds such as certain B vitamins and vitamin K.4

The microbiota is now recognized as having a profound effect on health and disease. Research is proceeding at an ever increasing pace to understand how a healthy and diverse microbiota can ensure good health for the body as a whole, providing protection against pathogens and stimulating the immune system. 1,4

What causes an unbalanced microbiota?

The microbiota comprises a unique balance of different bacterial species, and each person has their own distinctive microbiota. If the balance of the different micro - organisms living in the gut is disturbed, this can lead to a condition called dysbiosis, which may result in diarrhea and this may be chronic.1

A well - established cause of intestinal microbiota dysbiosis is the taking of antibiotics. This causes indiscriminate killing of bacteria in the microbiota and provides an opportunity for undesirable species to proliferate and some, such as Clostridium difficile may cause very serious disease.

Other factors which are able to upset the natural balance of the microbiota include: dietary changes, excessive alcohol or tobacco consumption, stress, disease and infections.1,2,4 Short - lived bacterial and viral infections of the intestine, which cause acute gastroenteritis, are also common causes of diarrhea, particularly in developing countries.8

Repeat or sustained gastrointestinal infections can bring about a change in the composition of the intestinal microbiota, damaging the protective microbial barrier, and this in turn leads to a worsening spiral of diarrhea, which may become chronic.8-10

What are the consequences of an unbalanced microbiota?

An unbalanced microbiota is often a cause of diarrhea. Diarrhea is the passage of 3 or more loose or liquid stools per day, or more frequently than is normal.11

An episode of diarrhea caused by bacterial or viral infection may lead to chronic diseases, such as irritable bowel disease (IBS). IBS is a common disorder that causes abdominal discomfort, bloating and diarrhea. ln most cases, the root cause of the IBS is unknown; however, in 5% to 32% of cases, IBS follows a bout of acute gastroenteritis.12

If the microbiota remains unbalanced for a longer period, it can cause excessive inflammation of the intestine, which is a characteristic of gastrointestinal autoimmune diseases like Crohn’s disease and ulcerative colitis. Balance can be restored to the microbiota by improving the diet, getting plenty of liquids and by taking probiotics or postbiotics.1,12,13 Certain probiotics and postbiotics have the dual effect of stimulating the healthy regrowth of the microbiota and substituting for it, this provides the protection and immune – stimulation that is lacking when the microbiota has been disturbed.9,13,14

  1. Valdes AM, Walter J, Segal E, Spector TD. Role of the gut microbiota in nutrition and health. BMJ 2018;361:k2179.
  2. Lebba V, Totino V, Gagliardi A, et al. Eubiosis and dysbiosis: the two sides of the microbiota. New Microbiol 2016;39:1-12.
  3. Shi N, Li N, Duan X, Niu H. Interaction between the gut microbiome and mucosal immune system. Mil Med Res 2017;4:14.
  4. Thursby E, Juge N. Introduction to the human gut microbiota. Biochem J 2017;474:1823-36.
  5. Gorbach SL. Microbiology of the gastrointestinal tract. In: Baron S, ed. Medical Microbiology. Galveston (TX): University of Texas Medical Branch at Galveston; 1996.
  6. Morowitz MJ, Carlisle EM, Alverdy JC. Contributions of intestinal bacteria to nutrition and metabolism in the critically ill. Surg Clin North Am 2011;91:771-85, viii.
  7. Lin L, Zhang J. Role of intestinal microbiota and metabolites on gut homeostasis and human diseases. BMC Immunol 2017;18:2.
  8. Pop M, Walker AW, Paulson J, et al. Diarrhea in young children from low-income countries leads to large-scale alterations in intestinal microbiota composition. Genome Biol 2014;15:R76.
  9. Sekirov I, Russell SL, Antunes LC, Finlay BB. Gut microbiota in health and disease. Physiol Rev 2010;90:859-904.
  10. Ma C, Wu X, Nawaz M, et al. Molecular characterization of fecal microbiota in patients with viral diarrhea. Curr Microbiol 2011;63:259-66.
  11. Diarrhoeal diseases. World Health Organization, 2017. (Accessed December 2020, at
  12. Thabane M, Marshall JK. Post-infectious irritable bowel syndrome. World J Gastroenterol 2009;15:3591-6.
  13. Patterson E, Cryan JF, Fitzgerald GF, Ross RP, Dinan TG, Stanton C. Gut microbiota, the pharmabiotics they produce and host health. Proc Nutr Soc 2014;73:477-89.
  14. Sánchez B, Delgado S, Blanco-Míguez A, Lourenço A, Gueimonde M, Margolles A. Probiotics, gut microbiota, and their influence on host health and disease. Mol Nutr Food Res 2017;61.

Diarrhea, a disease with many causes

Diarrhea describes the condition of having frequent, loose and watery stool, often caused by an infection of the gut.

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