Trillions of microbes inhabit the human body. New estimates show that there may be more microbes in the human body than total body cells. These microbes are collectively called microbiota1. Not only that, they have 50-100 times more genes than the human body. These genetic materials collectively form the microbiome1.

Here it is worth noticing that most of these bacteria are present in the gut. Perhaps the gut contains more than 80% of microbiota. Now the question arises regarding the role of so many microbes. They must be doing something, contributing to human health.

Science is still struggling to understand the role of such a massive number of microbes in the human body. However, they think that these microbes play a vital role in providing nutrients, training immunity, and much more. 

Good Bacterial and Role in Gut Health

When it comes to good bacteria, most of these few trillion microbes belong to three classes; Firmicutes, Bacteroidetes, and Actinobacteria. These bacteria have an essential role in maintaining good health. It now seems that humans cannot exist without these microbes1.

This good gut microbiota is especially good for metabolism and maintaining an adequate immune response. Many of its benefits are due to the production of metabolites like short-chain fatty acids (SCFAs), regulating metabolism, providing neurotransmitters, improving gut barrier function, and vitamins production. Therefore, these gut bacterial are vital in maintaining host immunity and neural health1.

Dysbiosis – Loss of Good Bacterial and Disease Development

Ever consider why metabolic disorders are increasing? Why are more people living with mood disorders, neurodegenerative conditions, cancers, and other issues? 

It is known that human genetics have not changed much in the last century or so. However, what has changed considerably is the environment, lifestyle, food choices, physical activity levels. These changes ultimately lead to disruption in the microbiota population.

Another critical reason for disruption in the microbiota population is the widespread use of antibiotics and other medications. 

Dysbiosis is both quantitative and qualitative changes in the gut microbiota. It means a reduced population of good microbes in the gut. However, not only that, but it also means qualitative changes and increased growth of harmful bacteria and other pathogens.

The final result of dysbiosis is quite challenging to predict and may differ in different individuals. Nonetheless, it is an important contributing factor to diseases like Alzheimer's, inflammatory bowel disease (IBD), Parkinson's, diabetes, cancers, obesity, hypertension, depression, chronic kidney disease, and much more1,2.

Although it is known that a decline in the population of good bacteria and an increasing gut population of bad bacterial causes these conditions, the underlying mechanism is poorly understood. Quite likely, these diseases are caused due to numerous reasons like reduced production of beneficial compounds, altered immune responses, and higher prevalence of low-grade inflammation. Some new studies confirm this link between dysbiosis and increased risk of non-infectious diseases like heart or brain disorders3.

Bad Bacterial in the Gut

How gut microbiota contributes to good health is still not fully understood, nor is the role of harmful bacterial growth in disease. However, it is known that this overgrowth of bad bacteria in the gut causes inflammation, lower production of bioactive compounds, altered immune responses, greater risk of opportunistic infections, and much more. 

It appears that this bacterial overgrowth or increased population of bad bacteria may have a role in almost every disease condition.

Although it is not possible to discuss every kind of harm that a bad bacterial population may do to health, we can look at some examples here.

Just consider the case of Clostridium difficile infection (CDI), which causes severe diarrhea in about half a million people in the US each year. It is among the leading causes of severe diarrhea. Now studies show that the primary cause of this infection is the depletion of good gut bacteria, leading to the overgrowth of C. difficile4. 

It is no secret that many people develop severe diarrhea after prolonged antibiotic therapy. Studies from the mid-20th century show that these gastrointestinal issues are due to the overgrowth of Candida albicans. C. Albicans is present in the human body. However, its overpopulation is harmful to health5. 

Similarly, in recent years, researchers have realized that many gut issues are due to small intestine bacterial overgrowth (SIBO) occurring due to a decline in the population of good bacteria. SIBO is common in irritable bowel disease, various functional gastrointestinal disorders, chronic liver disease, pancreatic disease6,7.

How can you Know About Dysbiosis or the Overgrowth of Bad Bacterial?

As science realizes that this altered gut bacterial population plays a vital role in the emergence of many diseases, both infective and non-infective illnesses, there is an increasing need to improve diagnostics. However, at present, there is no reliable test that may help in all cases, and thus doctors use different approaches.

One way to understand dysbiosis or overgrowth of bad bacteria could be a comprehensive stool analysis. This may not help get a complete picture, but it may still help understand what bacteria or yeast are causing the infection.

Similarly, SIBO can be diagnosed with the help of a test called the hydrogen breathe test8. 

There are other tests that may help, like endoscopy and even biopsy.

Here, it is vital to understand that no single test would provide a complete picture or help with a definitive diagnosis. However, using various tests of gastrointestinal function suggest changes in gut bacteria.

Promoting the Growth of Good Bacteria and Suppressing Bad Bacteria in the Gut

In the last few years, science has focused on boosting the population of good bacteria to manage various diseases. However, it is worth understanding that it is still an emerging science. Moreover, researchers know very little about boosting the population of good gut bacteria.

One of the most common approaches is using probiotics. These are food supplements containing beneficial bacteria like bifidobacteria, lactobacilli, enterococci, and even some yeasts like saccharomyces boulardii9. 

Another approach is to increase the intake of prebiotics. These are nutrients that promote the growth of good gut bacteria—Examples of prebiotics are inulin, beta-glucans, dietary fiber, and many more.

Final Thoughts

There are trillions of bacteria living in the human gut. They have many roles like producing bioactive compounds, neurotransmitters, training immunity, and much more. Therefore, any disruption in their population increases the risk of both infective and non-infective diseases. Thus, one of the ways of managing various health disorders is by promoting the growth of good bacteria in the gut.

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  1. Kho ZY, Lal SK. The Human Gut Microbiome – A Potential Controller of Wellness and Disease. Frontiers in Microbiology. 2018;9. Accessed March 6, 2022.
  2. Buttó LF, Haller D. Dysbiosis in intestinal inflammation: Cause or consequence. International Journal of Medical Microbiology. 2016;306(5):302-309. doi:10.1016/j.ijmm.2016.02.010
  3. van den Munckhof ICL, Kurilshikov A, Ter Horst R, et al. Role of gut microbiota in chronic low-grade inflammation as potential driver for atherosclerotic cardiovascular disease: a systematic review of human studies. Obes Rev. 2018;19(12):1719-1734. doi:10.1111/obr.12750
  4. Antharam VC, Li EC, Ishmael A, et al. Intestinal Dysbiosis and Depletion of Butyrogenic Bacteria in Clostridium difficile Infection and Nosocomial Diarrhea. Journal of Clinical Microbiology. 2013;51(9):2884-2892. doi:10.1128/JCM.00845-13
  5. Kumamoto CA, Gresnigt MS, Hube B. The gut, the bad and the harmless: Candida albicans as a commensal and opportunistic pathogen in the intestine. Current Opinion in Microbiology. 2020;56:7-15. doi:10.1016/j.mib.2020.05.006
  6. Quigley EMM. The Spectrum of Small Intestinal Bacterial Overgrowth (SIBO). Curr Gastroenterol Rep. 2019;21(1):3. doi:10.1007/s11894-019-0671-z
  7. Gunnarsdottir SA, Sadik R, Shev S, et al. Small intestinal motility disturbances and bacterial overgrowth in patients with liver cirrhosis and portal hypertension. The American Journal of Gastroenterology. 2003;98(6):1362-1370. doi:10.1016/S0002-9270(03)00250-8
  8. Rana SV, Malik A. Hydrogen Breath Tests in Gastrointestinal Diseases. Indian J Clin Biochem. 2014;29(4):398-405. doi:10.1007/s12291-014-0426-4
  9. Holzapfel WH, Schillinger U. Introduction to pre- and probiotics. Food Research International. 2002;35(2):109-116. doi:10.1016/S0963-9969(01)00171-5

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