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What is SIBO (small intestinal bacterial overgrowth) and its pathophysiology?

Small intestinal bacterial overgrowth (SIBO) arises when the number of bacteria in the small intestinal tract grows. It might cause you uncomfortable and bloated digestive issues.

It affects the small intestine and is quite dangerous. It happens when the number of microbes in the small intestine increases. These bacteria may exist in modest numbers and be regularly excreted from other regions of the gut. The result is discomfort and diarrhea. The bacteria start consuming the body’s nutrients, which can result in malnutrition.[1]


The gut is predominantly affected by SIBO symptoms. Some signs you might have to face are:

  • Stomach ache, particularly after eating
  • Gas
  • Constipation
  • Cramping
  • Diarrhea
  • Indigestion
  • Persistent sense of satiety


What is the real culprit? Well, the specific cause of SIBO is still not fully comprehended. It may happen when:

  • Anatomical anomalies exist in your small intestine.
  • PH variations in your small intestine
  • The immune system is malfunctioning.
  • When the small intestine’s muscles aren’t functioning properly, nutrients and microbes aren’t eliminated from the organ.

Risk factors

Have you ever wondered why you are more prone to SIBO? You may be at risk for SIBO if you have a gastrointestinal (GI) tract-related chronic illness or have had GI tract surgery [2]. You may also be more susceptible to developing some chronic diseases and ailments, such as:

  • Parkinson’s condition
  • Scleroderma (Systemic Sclerosis)
  • Diabetes
  • HIV
  • Hypothyroidism
  • Crohn’s illness
  • Using narcotics


When the regular homeostatic mechanisms that regulate intestinal populations of bacteria are thrown off, SIBO may occur. Decreased secretion of gastric acid and dysmotility of the small intestine are the two conditions that most frequently contribute to the overgrowth of bacteria. The chance of developing SIBO is further increased by anomalies in GI tract anatomy and disruptions in gut immune function. When bacterial overgrowth is already present, it may trigger a response of inflammation in the gut mucosa, aggravating the characteristic SIBO symptoms even more. Intestinal flora overgrowth in the small intestine can cause microscopic mucosal inflammation, albeit this is not always the case. [3]

Following are some other mechanisms that may contribute in the development of SIBO

  • Fermentable carbohydrates are used as fuel by oral bacteria that have overgrown in the small intestines to produce an excessive amount of gas throughout the intestine. Consequently, this results in common symptoms including bloating, gas, cramping in the abdomen, and irregular bowel motions. In actuality, this is a form of dysbiosis.
  • Because of the high bacterial density and associated problems, SIBO symptoms are more severe and occur more frequently. Inflammation of mucosa is the most significant of these. Small intestinal mucosa inflammation causes the brush boundary to disappear, reducing the area of the small intestine needed for the absorption of nutrients.[4]
  • A spike in the production of gases results from increased passage of fermentable sugars into the large intestine as a result of malabsorption brought on by mucosal inflammation. Due to damage to the brush border, those suffering from SIBO frequently exhibit a relative deficit of disaccharidases. Lactulose, sorbitol, and sucrose absorption in the small intestine is decreased as a result.
  • Another key aspect of SIBO is the bacterial deconjugation of bile acids. As a result, the jejunum instead of the ileum absorbs the free bile acids, which cause additional damage to the lumen of the intestine and decrease the production of micelle. Fat malabsorption, which results in a deficiency of nutrients that are fat-soluble like vitamins A, D, and E, is brought on by a shortage of micellar production. Because of insufficient cobalamin levels, this causes deficiencies in nutrition, causing neuropathy.

In conclusion, SIBO resembles to a loud bacterial party that causes discomfort in your small intestine. Although the precise causes are still unknown, abnormal anatomy and immunological problems may be involved. The outcomes? Issues with the absorption of nutrients and inflammation. 

Disclaimer: As always, this is not medical advice, just information regarding SIBO, so check with your medical professional to review your symptoms as well as medical options that may help address your condition. Before starting any of these things mentioned above, it is best to receive an individualized approach to see what may best work with you by a medical professional. 


[1] C. E. King and P. P. Toskes, “Small Intestine Bacterial Overgrowth,” Gastroenterology, vol. 76, no. 5, pp. 1035–1055, May 1979, doi: 10.1016/S0016-5085(79)91337-4.

[2] A. C. Dukowicz, B. E. Lacy, and G. M. Levine, “Small Intestinal Bacterial Overgrowth,” Gastroenterol. Hepatol., vol. 3, no. 2, pp. 112–122, Feb. 2007, Accessed: Jul. 10, 2023. [Online]. Available:

[3] “Small bowel bacterial overgrowth: MedlinePlus Medical Encyclopedia.” (accessed Jul. 10, 2023).

[4] E. J. Krajicek and S. L. Hansel, “Small Intestinal Bacterial Overgrowth,” Mayo Clin. Proc., vol. 91, no. 12, pp. 1828–1833, Dec. 2016, doi: 10.1016/j.mayocp.2016.07.025.

Dr. Tyrrell Jenkins

Hi, I'm Dr. TJ

Health Coach + Experienced Physician

Dr. Tyrrell Jenkins, affectionately known as Dr. TJ, has practiced medicine in 4 areas, including outpatient primary care, urgent care, hospital medicine, and the intensive care unit, which are all unique and have given him a significant breath of clinical experience that many physicians do not possess. This has allowed him to assess and manage the continuum of diseases.


1:1 Private Coaching

Private 1:1 coaching program is specifically for those who have struggled and become frustrated with their thyroid dysfunction, irritable bowel syndrome (IBS), or small intestinal bacterial overgrowth (SIBO) condition. This private coaching is for those who have tried restrictive diets and feel that they are going in circles with no improvement. This is for those who are looking to fast track their progress with a personalized approach.

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