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What is SIBO?

Before we dive in, here's an anatomy check on what's inside the abdomen. After the stomach - where food is churned - food enters the small intestine. The small intestine absorbs most nutrients from our food. Normally, the small intestine has some bacteria, but not very much. Next, food enters the large intestine AKA the colon, where lots of healthy bacteria live and a few other nutrients are absorbed. Lastly, food enters the rectum and is excreted as stool.

An image of a human skeleton in white against a black background. The skeleton is shown in detail, with all the bones clearly visible. Superimposed on the skeleton are the intestines, which have been highlighted in red to distinguish them from the bones. The red intestines follow their natural path in the abdominal cavity, providing a clear contrast to the white skeleton.

SIBO, small intestinal bacterial overgrowth, is when there is too much bacteria in the small intestine. Bacterial overgrowth can cause symptoms such as bloating, gas, abdominal pain, constipation and/or diarrhea, nausea, and heartburn. SIBO is a common cause of IBS, and they often present with the same symptoms. SIBO can also cause symptoms outside of the GI tract, such as headaches, fatigue, joint pain, depression, anxiety, and skin disorders.

SIBO can occur from a variety of causes. It's important to access medical history, past medication use, digestive function, and each person's anatomy to find what may cause SIBO and more importantly how to prevent it from coming back.

SIBO is diagnosed with a breath test, called a lactulose breath test. Lactulose is a sugar that humans can't digest, but bacteria can. When bacteria eat this sugar, they produce gas, either methane or hydrogen. The breath test measures these gases and helps diagnose bacteria in the small intestine. Hydrogen gases can cause a lot of the above symptoms, but there are two additional types of organism overgrowth in the intestine that can lead to similar symptoms as SIBO.

Alongside SIBO, there is intestinal methanogenic overgrowth (IMO) and excess hydrogen sulfide. These conditions can also contribute to digestive discomfort and other related issues. Understanding the distinctions between these different types of overgrowth is crucial in order to effectively get rid of and prevent SIBO from coming back. Now that we have explored SIBO and its counterparts, let's delve into each of these conditions in more detail.


This is a newish term for when there is specifically too much methane in the intestines. Intestinal methanogenic overgrowth, or IMO, refers to an excessive growth of methane-producing organisms called methanogens in the small and large intestines. It used to be called "methane SIBO," but that term is not entirely accurate. Unlike bacteria, which are typically associated with SIBO, methanogens are a type of single-celled organism, called archaea. These methanogens can overgrow not only in the small intestine but also in the colon.


Patients with IMO experience similar symptoms to SIBO, including abdominal pain, bloating, gas, distension, and especially constipation. The severity of constipation is linked to the level of methane measured in a breath test. These symptoms typically occur once a week or more for at least four weeks. IMO also shares many symptoms with IBS-C (constipation-predominant irritable bowel syndrome) and IBS-M (mixed-diarrhea/constipation irritable bowel syndrome).

When we use a breath test to measure methane, we look for high levels of methane. Elevated levels of methane are linked to constipation.


When treating SIBO with IMO, it's best to more than one antimicrobial agent, usually a combination of herbs or a combination of medications.


Excess hydrogen sulfide occurs when there is an overgrowth of organisms that produce hydrogen sulfide. This one is tricky because on a regular breath test, the results will look "flatlined", which some people may interpret as a normal test. There is a particular breath test that looks for hydrogen sulfide.


Patients with excess hydrogen sulfide experience similar symptoms to those with SIBO (small intestinal bacterial overgrowth): abdominal pain, bloating, gas, distension, and especially diarrhea. The severity of diarrhea is linked to the levels of hydrogen sulfide measured through a breath test. These symptoms typically occur at least once a week for a duration of four weeks or more. Excess hydrogen sulfide shares many symptoms with IBS-D (diarrhea-predominant irritable bowel syndrome) and IBS-M (mixed-diarrhea/constipation irritable bowel syndrome).


Using bismuth subsalicylate to treat subjects resulted in a significant (>95%) decrease in the release of hydrogen sulfide in their feces. Additionally, there is strong evidence that antibiotics such as rifaximin can effectively reduce symptoms associated with IBS-D, such as chronic diarrhea.

To learn more about the diagnosis and treatment of SIBO, IMO, or excess hydrogen sulfide, let's let up a visit! Our team is dedicated to providing comprehensive information and personalized care to address your specific needs


Pimentel, M., Saad, R., Long, M., & Rao, S. ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. The American Journal of Gastroenterology, 2020.

Rezaie, A., Buresi, M., Lembo, A., Lin, H., McCallum, R., Rao, S., Schmulson, M., Valdovinos, M., Zakko, S., & Pimentel, M. Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus. American Journal of Gastroenterology, 2017.

Lacy, B., Pimentel, M., Brenner, D., Chey, W., Keefer, L., Long, M., & Moshiree, B. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. The American Journal of Gastroenterology, 2021.

Pimentel, M., Hosseini, A., Chang, C., Mathur, R., Rashid, M., Sedighi, R., Fowler, H., Torosyan, J., Wang, J., & Rezaie, A. Exhaled Hydrogen Sulfide Is Increased in Patients With Diarrhea: Results of a Novel Collection and Breath Testing Device. AGA Abstracts, 2021.

Rezaie, A., Zeev, H., McCallum, R., & Pimentel, M. Lactulose Breath Testing as a Predictor of Response to Rifaximin in Patients With Irritable Bowel Syndrome With Diarrhea. The American Journal of Gastroenterology, 2019.

Pimentel, M., Chatterjee, S., Chow, E., Park, S., & Kong, Y. Neomycin improves constipation-predominant irritable bowel syndrome in a fashion that is dependent on the presence of methane gas: subanalysis of a double-blind randomized controlled study. Digestive Disease and Sciences, 2006.

Low, K., Hwang, L., Hua, J., Zhu, A., Morales, W., & Pimentel, M. A Combination of Rifaximin and Neomycin Is Most Effective in Treating Irritable Bowel Syndrome Patients With Methane on Lactulose Breath Test. Journal of Clinical Gastroenterology, 2010.

Suarez, F., Furne, J., Springfield, J., & Levitt, M. Bismuth subsalicylate markedly decreases hydrogen sulfide release in the human colon. Gastroenterology, 1998.

Singer-Englar, T., Rezaie, A., Gupta, K., Pichetshote, N., Sedighi, R., Lin, E., Chua, K., & Pimentel, M. Competitive Hydrogen Gas Utilization by Methane- and Hydrogen Sulfide-Producing Microorganisms and Associated Symptoms: Results of a Novel 4-Gas Breath Test Machine. AGA Abstracts, 2021.

Pimentel, M., Mathur, R., & Chang, C. Gas and the Microbiome. Current Gastroenterology, 2013.

Singer-Englar, T., Rezaie, A., Gupta, K., Pichetshote, N., Sedighi, R., Lin, E., Chua, K., & Pimentel, M. Validation of a 4-Gas Device for Breath Testing in the Determination of Small Intestinal Bacterial Overgrowth. AGA Abstracts, 2018.

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