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The path to treatment for SIBO (small intestinal bacterial overgrowth), IMO (intestinal methanogenic overgrowth), and excess hydrogen sulfide starts with a clinical diagnosis aided by a breath test. Each of these conditions in the gut microbiome can be managed with a personalized treatment plan prescribed by a doctor, so that patients can start feeling better quickly. 

From antibiotics to dietary lifestyle changes, there are evidence-based SIBO treatments suggested in the American College of Gastroenterology Clinical Guideline for Small Intestinal Bacterial Overgrowth.


Small intestinal bacterial overgrowth, or SIBO, is defined as the presence of excessive numbers of bacteria in the small bowel causing frustrating and often painful gastrointestinal symptoms. The small intestine usually has lower levels of bacteria than the colon. When there is an overgrowth of bacteria in the small intestine, the normal balance in the gut microbiome is significantly disrupted.



Patients with SIBO often experience bloating, abdominal pain, gas, distension, flatulence, and diarrhea. These symptoms can masquerade as other illnesses. The symptom most commonly reported by patients with SIBO is bloating, often after eating. These symptoms are usually experienced once a week or more for at least four weeks.



When measured by a breath test, the threshold of hydrogen is calculated by adding 20 ppm to the baseline. A rise in hydrogen levels by 20 ppm or more within 90 minutes is supportive of SIBO. 



The ACG Clinical Guideline for SIBO suggests the use of antibiotics in symptomatic patients to eradicate overgrowth and resolve symptoms. Recent data suggests that the optimal benefit of the antibiotic rifaximin was seen in subjects with IBS symptoms with abnormal hydrogen levels.


Intestinal methanogenic overgrowth, or IMO, is an overgrowth of methane-producing archaea in the small and large intestines.  This condition was previously called “methane SIBO;” however, that term isn’t quite accurate. Methanogens are not bacteria (the “B” in SIBO) but are archaea, a group of single-celled organisms lacking a defined nucleus. These methanogens may also overgrow in the colon and not just the small intestine (the “SI” in SIBO).  



Patients with IMO experience symptoms similar to SIBO: abdominal pain, bloating, gas, distension, flatulence, but especially constipation.  The level of methane measured by a breath test correlates with the severity of constipation. These symptoms are usually experienced 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 measured by a breath test, the threshold for methane is always 10 ppm. Levels of methane that are 10 ppm or more at any point during the breath test are considered abnormal. Elevated levels are associated with constipation.



The ACG Clinical Guideline for SIBO suggests that IMO treatment may require more than one antimicrobial agent. Research shows that patients who received a combination of rifaximin and neomycin showed a higher rate of methane eradication on breath testing compared to patients who received either rifaximin or neomycin alone.


Excess hydrogen sulfide is a condition that results in the overgrowth of hydrogen sulfide-producing organisms. Excess hydrogen sulfide was previously undetectable by other breath tests prior to Trio-Smart. Patients with elevated hydrogen sulfide levels may have appeared “normal” on previous breath tests. 



Patients with excess hydrogen sulfide share common symptoms with SIBO: abdominal pain, bloating, gas, distension, flatulence, but especially diarrhea. Levels of hydrogen sulfide, as measured by a breath test, correlate with the severity of diarrhea. These symptoms are usually experienced once a week or more for at least four weeks. Excess hydrogen sulfide shares many of the symptoms of IBS-D (diarrhea-predominant irritable bowel syndrome) and IBS-M (mixed-diarrhea/constipation irritable bowel syndrome).  



When measured by a breath test, the threshold for hydrogen sulfide is always 3 ppm. Levels of hydrogen sulfide that are 3 ppm or more at any point during the breath test are considered excess and are associated with diarrhea.



Data shows treatment of subjects with bismuth subsalicylate produced a >95% reduction in fecal hydrogen sulfide release. There is also strong evidence that antibiotics like rifaximin can be effective in the reduction of correlating IBS-D symptoms, like chronic diarrhea.


The Low FODMAP Diet is a food category diet based on research conducted at Monash University, one of Australia's leading public research universities. Researchers at Monash have found that up to 75% of people with IBS feel better on the Low FODMAP Diet during the elimination phase.


Highly fermentable foods are filled with short-chain carbohydrates that don’t get fully absorbed by the small intestine and in turn start to ferment in the colon, exacerbating IBS symptoms. The Low FODMAP Diet is a three-phase diet designed to help you eliminate, reintroduce, and avoid foods with these types of carbohydrates. 


Monash University defines the FODMAP acronym as:


Fermentable -  The process of bacteria in the gut fermenting unabsorbed carbohydrates into gas

Oligosaccharides (Fructans) - Found in foods such as wheat, rye, onions, garlic, and legumes/pulses

Disaccharides (Lactose) - Found in dairy products like milk, soft cheeses, and yogurts

Monosaccharides (Fructose) - Found in honey, apples, and high-fructose corn syrups


Polyols (Sorbitol and Mannitol) - Found in some fruits and vegetables and used as artificial sweeteners


In the first phase of the Low FODMAP Diet, the patient eliminates all highly fermentable foods from their diet for 2-6 weeks. In the second phase which lasts 8-12 weeks, the patient slowly reintroduces fermentable foods one at a time. This allows the patient to identify the exact foods that could be contributing to their IBS symptoms. 


In the final phase, patients will have a better understanding of which foods they should avoid and consume and can then integrate this change into their daily lifestyle, hopefully leading to less intrusive IBS symptoms.


Low Fermentation Eating (LFE) supports a more balanced microbiome by decreasing the amount of the fermented foods in a patient's diet. Developed by Mark Pimentel, MD and Ali Rezaie, MD, LFE is specifically designed for those patients suffering from SIBO and IBS symptoms like bloating, gas, constipation, and diarrhea.



Low Fermentation Eating is based on two parts: restricting foods with high carbohydrates and meal timing. When carbohydrates cannot be properly broken down, the bacteria in the gut then digest the sugars, releasing gases like hydrogen, methane, and hydrogen sulfide that can result in frustrating GI symptoms. Additionally, spacing out meal times with four to five hours between consumption allows for gut-cleaning waves. 



Non-absorbable common sugar substitutes like sucralose, sorbitol, lactitol, xylitol, mannitol, and stevia are some of the top foods to avoid, because they cannot be digested by humans and instead feed the bacteria in the gut directly. High-fiber foods and foods with inulin, a type of prebiotic, are also considered troublesome. Foods like lentils, beans, soy products, and dairy products like milk, cheese, and yogurt are considered “fermentable” foods, as they can be difficult to digest and excessively feed the bacteria in the gastrointestinal tract. They should be avoided, as well.



The gut is self-cleaning, and it’s very important not to disrupt these natural gut-cleaning waves with food digestion. The gut-cleaning waves cannot occur until fasting. The feeding part of digestion ends within three hours of eating, and it’s suggested to have two gut-cleaning cycles before eating again. That means that leaving four to five hours between meals can support a more regular and proper cleaning cycle.

To learn more about Low Fermentation Eating (LFE) and get tasty recipes, please visit


Treating SIBO, IMO, and excess hydrogen sulfide conditions begins with a clear understanding of the three fermented gases in the microbiome by way of a breath test. Determining the specific illness and root cause helps doctors confidently provide personalized treatment to help patients feel better quickly.



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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