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The 5 Types of SIBO and Connection to Other Health Conditions

Bits of Wisdom


A healthy microbiome is critical for wellness. So it is important to pay attention to the balance of the microbiome in the colon and consider the amount and diversity of bacteria, yeast, and other organisms. But what happens when organisms from the colon migrate into the small intestine? A condition called Small Intestinal Bacterial Overgrowth (SIBO).

What is SIBO?

Small intestinal bacterial overgrowth (SIBO) is an increase in bacteria in the small intestine. The small intestine should have relatively small amounts of bacteria, but when levels increase, bacteria ferment carbohydrates in the diet producing gas. 

SIBO symptoms include:

Just as symptoms of SIBO will vary from person to person, so will root causes.

Contributors include:

Individuals with an autoimmune disease like Crohn’s and celiac disease are at a higher risk for SIBO. 

Next, let’s explore the five different types of SIBO. 

Hydrogen Dominant SIBO

Hydrogen dominant SIBO is characterized by bacteria in the small intestine that produce hydrogen gas. This is the most prevalent type of SIBO. 

Methane Dominant SIBO

Methane dominant SIBO is characterized by an overgrowth of methane-producing bacteria in the small intestine. This SIBO type is associated with constipation and is also referred to as intestinal methanogen overgrowth, or IMO. 

Mixed SIBO

Mixed SIBO occurs when both hydrogen gas and methane gas are elevated on a SIBO breath test, suggesting overgrowth of both methane-producing and hydrogen-producing bacteria. 

Hydrogen Sulfide Dominant SIBO 

This type of SIBO occurs when bacteria in the small intestine consume the hydrogen gas made by other bacteria to produce hydrogen sulfide, the gas that smells like rotten eggs. Hydrogen Sulfide SIBO may correlate with diarrhea. 


SIFO, or small intestinal fungal overgrowth, occurs when fungi – not bacteria – migrate into the small intestine. SIFO has similar symptoms and triggers as SIBO, and we continue to learn more as research on this condition emerges. 

Symptoms of SIBO Vs. IBS

You may have noticed that SIBO symptoms sound quite similar to irritable bowel syndrome, (or IBS), which is a collection which includes abdominal pain and changes in stool frequency and consistency. IBS may be diagnosed when other GI conditions don’t explain symptoms. However, we now know that up to 78% of IBS cases may be due to SIBO. This is good news because it gives hope to IBS sufferers that SIBO treatment may resolve symptoms.  

...we now know that up to 78% of IBS cases may be due to SIBO. This is good news because it gives hope to IBS sufferers that SIBO treatment may resolve symptoms. 

SIBO and Histamine Intolerance

Histamine is a normal chemical that the immune system uses to fight pathogens. Histamine intolerance occurs when histamine is released faster than it can be broken down. As an example, seasonal allergies correlate with high histamine levels.

Histamine intolerance symptoms include:

SIBO and histamine intolerance are linked in that SIBO may be the root cause of histamine intolerance symptoms. Some bacteria are histamine producers, and bacterial overgrowth may increase histamine levels. In addition, SIBO, infections, and digestive issues may make it more difficult to break down histamine. 

SIBO and Autoimmune Disease

In some cases, autoimmunity may be one of the root causes of SIBO. We must look at the migrating motor complex, or MMC to understand this connection. The MMC is the muscle contractions that help clear the intestines between meals and move everything in a downward motion. When the MMC is impaired, SIBO can develop. 

While there are many reasons behind MMC dysfunction, one is high levels of antibodies after a food poising event. Specific antibodies can trigger an autoimmune attack of the MMC muscles. All autoimmune disease is associated with a similar pattern where an environmental antigen triggers the autoimmune process. 

I hope you enjoyed this overview of SIBO. In my next article in this series, I will dive into treatment options from a functional medicine perspective. 


  1. Bures, J., Cyrany, J., Kohoutova, D., Förstl, M., Rejchrt, S., Kvetina, J., Vorisek, V., & Kopacova, M. (2010). Small intestinal bacterial overgrowth syndrome. World journal of gastroenterology, 16(24), 2978–2990. 
  2. Rao, S., & Bhagatwala, J. (2019). Small Intestinal Bacterial Overgrowth: Clinical Features and Therapeutic Management. Clinical and translational gastroenterology, 10(10), e00078. 
  3. Birg, A., Hu, S., & Lin, H. C. (2019). Reevaluating our understanding of lactulose breath tests by incorporating hydrogen sulfide measurements. JGH open : an open access journal of gastroenterology and hepatology, 3(3), 228–233. 
  4. Erdogan A, Rao SS. Small intestinal fungal overgrowth. Curr Gastroenterol Rep. 2015 Apr;17(4):16. 
  5. Ghoshal, U. C., Shukla, R., & Ghoshal, U. (2017). Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome: A Bridge between Functional Organic Dichotomy. Gut and liver, 11(2), 196–208. 
  6. Takakura, W., & Pimentel, M. (2020). Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome - An Update. Frontiers in psychiatry, 11, 664. 


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