Maintaining a gut microbiota in good shape plays a key role in maintaining immunity and overall health. Disorders in the composition and/or functions of the gut microbiota such as small intestinal bacterial overgrowth (SIBO), vaguely referred to as ‘dysbiosis’, have been involved in a range of symptoms in the gut and beyond.
SIBO is defined as the presence of abnormal and excessive bacteria in the small intestine that produces gastrointestinal symptoms. SIBO bacteria may come from the colon and it is also true that bacteria in the small intestine are different from bacteria in the colon and in the stools. New findings from the REIMAGINE study show that two bacteria species -namely Escherichia coli and Klebsiella pneumoniae– are increased in the small bowel microbiota in patients with SIBO and correlate with the severity of abdominal pain, diarrhea, and bloating.
SIBO is commonly associated with a range of non-specific gastrointestinal symptoms involving diarrhea, constipation, alternating bowel habits, bloating, abdominal pain, or discomfort and extradigestive symptoms such as fatigue, anxiety, brain fog, or chronic pain.
Depending on the microorganism involved, intestinal microbial overgrowth is classified into three categories: SIBO (if there is bacterial overgrowth), intestinal methanogen overgrowth (IMO), and small intestinal fungal overgrowth (SIFO). While in SIBO there is an overproduction of hydrogen and/or sulfide, in the presence of IMO, methane overproduction is the rule. No particular gas has been so far associated with SIFO.
While the increase in the number of SIBO studies is modest, the over-diffusion of SIBO in social media is exponential and involves health risks
In normal conditions, the small intestine harbors a much lower microbial content compared to the oral cavity and the colon and looks much more like a fast-flowing stream than a swamp. The overgrowth of bacteria in the small intestine has its roots in the loss of physical and chemical barriers that naturally prevent the proliferation of bacteria in this part of the intestine. These barriers include gastric acid, juices produced by the pancreas and liver that help digesting foods, natural movements of the small intestine (“housekeeping waves” that occur every 90 to 120 minutes during fasting), intestinal barrier integrity, the gut microbiota, and ileocecal valve, which is a physical barrier at the end of the small intestine that prevents fecal content or microbiota returning from the large intestine to the small intestine.
Javier Santos, gastroenterologist at the Vall d’Hebron University Hospital; Director of the Physiology and Pathophysiology of the Digestive Tract research group at VHIR; CIBERehd, explained to GMFH editors via email that stressful modern life, poor quality of food, food additives, and high consumption of medications are some of the causes of the current rise of SIBO. “As everything spreads very quickly now through the social media, and the symptoms of SIBO are very unspecific and common to many people and to different pathologies, it seems that SIBO has increased, but the increase in the number of SIBO studies in PubMed -the largest database of scientific studies- is modest” highlighted Santos.
SIBO is not a new field
SIBO is not something new. Indeed, gastroenterologists have been familiar with SIBO since the 50’s and 60’s as it was related to conditions related to maldigestion or malabsorption. Santos explained that the scientific concept of SIBO has shifted from a complication associated with gastrointestinal surgery, the presence of intestinal motility disorders such as scleroderma or diabetes or insufficient stomach acid production, to an epidemic disorder that is present in otherwise healthy populations. SIBO is also common in patients with IBS-like symptoms, as approximately 35% of all IBS patients have SIBO at some time point in their lives.
While the cause of intestinal microbial overgrowth is not fully clear in all patients, any situation that blocks the bowel or slows down the gut may potentially lead to SIBO: food poisoning has been identified recently as a cause of transit-slowing in the small intestine in rats.
Medication that alters gut motility such as antibiotics, opioids, and anticholinergics may also favor bacterial overgrowth in certain individuals. However, Santos acknowledged that it is common for patients with SIBO to also have unjustified fears about the use of foods such as gluten and medicines such as omeprazole because of their potential to cause SIBO, while this relationship is mostly unproven.
Breath tests lead to false diagnoses of SIBO
The primary and easiest method for diagnosing SIBO is through a breath test, which quantifies exhaled hydrogen and methane that come exclusively from microorganisms in the gut. Culturing juice from the contents of the small intestine is the other way to diagnose SIBO, while it is not used as a routine procedure by physicians. On the other hand, SIFO can only be diagnosed through aspiration and culture of small bowel contents and IMO can only be diagnosed with breath tests. It is important to note that clinical symptoms and response to antibiotics cannot accurately diagnose SIBO.
Regarding the interpretation of the results of breath tests, Santos explained that an increase in H2 concentrations of ≥20 ppm from baseline is diagnostic of SIBO, while the presence of CH4 levels of ≥10 ppm is diagnostic of IMO, when these changes happen in the first 90 min of the test. While nowadays it is not yet possible to determine the presence of hydrogen sulfide through a breath test in Europe, it is suggested to ask the patient about the odor of the wind, which, if very unpleasant (“rotten eggs”), may indicate excessive production of this malodorous gas.
However, breath tests can lead to many false diagnoses due to their low specificity for diagnosing SIBO, which can lead to an overdiagnosis of SIBO. When breath tests are applied to all people that have abdominal discomfort and they give positive results, the next step is giving them non-absorbable broad-spectrum antibiotics, with all the health risks associated with inappropriate antibiotic use, such as interference with the gut microbiota and increased risk of antibiotic resistance. Santos believes that the main limitations of breath tests for diagnosing SIBO and IMO are the lack of standardization, variations in transit time, contamination, and also errors in test preparation and development, which can be overcome if conducted in specialized settings.
The three pillars to follow when managing SIBO: identifying the cause, treating the SIBO, and preventing the recurrence of SIBO
Managing SIBO involves identifying the main cause, treating the SIBO, and preventing its recurrence in the future. According to Santos: “Treating SIBO is based on identifying and correcting its underlying causes if possible (e.g., withdrawal of transit-slowing drugs such as opioids) to reduce recurrences, correcting nutritional deficiencies, and when there is evidence, not suspicion, of overgrowth, providing antibiotic treatment.”
In patients in which the underlying cause of SIBO cannot be corrected (e.g., patients with diabetes, scleroderma, or immunodeficiency), the treatment must be personalized, combining antibiotic therapies with other therapies that help maintain intestinal and microbiota balance and do not cause harm. Among these modalities, nutrition is a central pillar and should be guided by an expert professional and retreatment with antibiotics should be reserved for patients with highly recurrent SIBO (>4 episodes/year), explained Santos.
When inducing the remission of SIBO, following an elemental diet has proven to be effective in ameliorating SIBO symptoms in IBS patients and in normalizing the breath test (80% after 2 weeks and 85% after 3 weeks of therapy). However, the cost and taste involved in elemental diet formulations are the main factors limiting its use. Reduction of sulfur-rich foods could be useful if sulfur SIBO is suspected although there is no evidence of this.
Plant-based antimicrobials are increasingly being used as an alternative to antibiotics or in patients who do not respond well to antibiotics. However, no data have provided an improvement in symptoms and correct dosing, safety profile of preparations used, and potential drug interactions of the compounds are the main shortcomings of antimicrobial herbs.
When it comes to maintaining control or preventing the recurrence of SIBO, a low FODMAP diet reducing fermentable products (fiber, alcohol, sugars, sweeteners and prebiotics such as inulin) is associated with less fermentation but is supported by low quality evidence and should be used for short periods of time to avoid unnecessary food restriction. Santos explains that certain studies favor the use of prebiotics over the FODMAP diet, while others favor the addition of 5g/day of guar gum (10 days) to improve the symptomatic response and eradication rate with rifaximin in patients with SIBO.
Facilitating and improving gut motility with prokinetic medications (e.g., octreotide, cisapride, tegaserod, erythromycin, pyridostigmine, peppermint oil, linaclotide, and prucalopride) might help patients to maintain remission, although published studies are scarce. The use of probiotics in the management of SIBO remains controversial. While probiotics could decontaminate SIBO and relieve abdominal pain -but are not useful in preventing SIBO-, emerging data has linked probiotics to brain fog, a rise in methane production, and fullness and distension after meals.
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