Hydrogen, Methane, and Hydrogen Sulfide
Multiple patients, all diagnosed with SIBO, may experience very different symptoms. Research indicates that the type of organism overgrowth occurring in your microbiome can determine digestive issues. An excess of bacteria can produce hydrogen dominant SIBO, and/or increased production of hydrogen sulphide, while an excess of archaea can produce methane dominant SIBO. Additionally, you can experience a combination of bacteria and archaea overgrowth.
Hydrogen Dominant Bacteria
Small intestinal bacterial overgrowth (SIBO) is characterized by an overgrowth of bacteria and/or archaea in the small intestine. An overgrowth of bacteria will lead to the fermentation of carbohydrates. This process creates hydrogen gas as a by-product, leading to hydrogen dominant SIBO, sometimes described as SIBO-D (1). During breath testing, hydrogen levels will be elevated in hydrogen dominant SIBO. When bacteria produce hydrogen, additional byproducts are produced that irritate the intestinal lining, decrease absorption of nutrients, and lead to diarrhea (1). In cases of hydrogen dominant SIBO, targeted treatment to decrease hydrogen-producing bacteria is required, in addition to treating the root cause that led to the development of SIBO (The 9 Causes of SIBO That Has You Struggling).
Methane Dominant Archaea
In addition to bacteria, the microbiome also contains single-celled organisms known as archaea. Similar to bacteria, archaea can overgrow, leading to dysbiosis. When bacteria feed off of carbohydrates, they produce hydrogen. Archaea consume hydrogen and produce methane as a byproduct of digestion. An abundance of archaea leads to an excess of methane gas, leading to bloating as well as slowed transit time –how quickly food moves through the digestive tract. Slowed transit time leads to constipation, allowing more bacteria to grow, resulting in increased methane and thus, worsened constipation (2). The classic presentation of methane dominant SIBO, also known as SIBO-C, is constipation.
Treatment aimed at killing off hydrogen-producing bacteria will help to deplete the food source for archaea but they can survive for a while without hydrogen. Archaea also form biofilms, a protective layer, making them more difficult to treat (3). Treating SIBO-C requires targeted approaches to improve gut motility, decrease levels of both hydrogen-producing bacteria and archaea, and destroy the protective biofilm surrounding archaea communities.
Hydrogen Sulphide Producing Bacteria
While less common, hydrogen sulphide production as a result of bacterial overgrowth is gaining more attention as a contributor to gut inflammation (4). Similar to other bacteria, sulphate-reducing bacteria (SRB) appears to be necessary for normal and healthy gut functioning if levels of these bacteria are regulated and maintained within the large intestine (4). However, when overgrowth occurs and migrates to the small intestine, symptoms can result (5). The hallmark symptom of sulphate-reducing bacteria (SRB) in the small intestine is ‘rotten egg’ odour gas, the result of the hydrogen sulphide gas that SRB produce (6). SRB can consume sulphate, or, like Archaea, these bacteria can consume hydrogen. However, rather than competing with archaea, they appear to complement each other and may contribute to balance within these communities (7). Due to this function, a certain amount of SRB appears to be essential, but an overgrowth can be detrimental (6). An excess of hydrogen sulphide may contribute to a variety of conditions such as chronic fatigue syndrome, inflammatory bowel disease, colon cancer, irritable bowel syndrome (8,9,10,11). Genetic mutations in genes that regulate detoxification of sulphur and hydrogen sulphide may contribute to elevations in sulphur levels (12). Currently, there is not a SIBO breath test that is able to specifically test for SRB; patients with elevated SRB may test negative for SIBO while still experiencing symptoms as a result of a bacterial overgrowth of SRB (5). As in other cases of SIBO, promoting gut motility is essential in addition to decreasing bacterial overgrowth and determining the root cause of overgrowth. Additionally, consuming a diet low in sulphur and introducing nutrients that promote sulphur detoxification may also reduce symptoms.
Interested in learning more about the treatment of SIBO? (SIBO: Treatment)