Decoding SIBO
Demystifying the Types of SIBO, Symptoms, Causes, Testing, & Treatment Options
Living with digestive symptoms can be incredibly challenging because they can have a significant impact on your daily life. From frequent abdominal pain and bloating to diarrhea and constipation, navigating through each day can feel like an uphill battle, one that’s especially daunting when you’re unsure of why the symptoms are occurring in the first place.
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But within your digestive tract, a delicate balance exists between beneficial and harmful bacteria. If this equilibrium becomes unbalanced, large amounts of certain types of bacteria may begin to grow in your small intestine (or small bowel), causing unpleasant symptoms, such as bloating, abdominal pain, diarrhea, and gas. An excessive amount of bacteria in the small intestine can lead to a condition known as small intestinal bacterial overgrowth (SIBO).
An astounding 30 million Americans likely have SIBO, and research suggests the rate of SIBO may be as high as 78% in people diagnosed with irritable bowel syndrome (IBS). Despite its prevalence, SIBO itself often goes undiagnosed, leaving many people grappling with mysterious symptoms.
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If you suspect you may be dealing with SIBO symptoms, you’re already aware of the adverse impact it can have on your quality of life. These negative effects underscore the importance of better understanding SIBO, the factors that contribute to it, and its influence on digestive health.
SIBO is an acronym for a medical condition called “small intestinal bacterial overgrowth.” This means your small intestine has too many bacteria or an unhealthy overgrowth of them, especially ones not typically found in that part of the digestive tract.
What is SIBO?
Normally, the small intestine contains relatively few bacteria compared to the large intestine or colon. However, with SIBO, bacteria from the colon migrate and take up residence in the small intestine, leading to an overgrowth.
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This overpopulation of bacteria starts feasting on your dietary nutrients before your body can fully digest and absorb them. As the bacteria consume the food passing through, they produce excess gases as a byproduct. It's this gaseous overproduction that leads to the hallmark SIBO symptoms like bloating, abdominal pain, diarrhea, and flatulence.
When bacteria exist in their proper territories and quantities, digestion hums along undisturbed. But when their balance gets disrupted through migration and overgrowth, SIBO's unpleasant digestive woes can take over your daily life.
What are the symptoms of SIBO?
If you have SIBO, the symptoms may be different from one person to another, and many symptoms closely overlap with those of IBS or other conditions affecting the gastrointestinal (GI) tract.
Your symptoms can range in severity and intensity and may include:
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abdominal pain
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bloating
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diarrhea
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constipation
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decreased appetite
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distended abdomen
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feeling of fullness
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indigestion
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gas
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nausea
Some people with SIBO may also experience fatigue, unexplained weight loss, vitamin and mineral deficiencies, or malabsorption (difficulty absorbing nutrients).
What are the causes of SIBO?
Over the last two decades, doctors have made great strides toward understanding the causes of SIBO. To date, researchers have identified several factors that may contribute to the condition. They include the following:
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Impaired motility
Dr. Mark Pimentel, a renowned IBS and SIBO expert, compares the colon to a "swamp" environment where bacteria thrive, while the small intestine should mimic a fast-flowing "river" to keep bacteria moving along. Anything that slows or stalls this river's momentum can disrupt the small intestine's self-cleaning process and lead to bacterial overgrowth.
Under normal circumstances, the small intestine uses peristaltic muscular contractions every 90-120 minutes in a "housekeeping" wave to propel contents and clear out any lingering bacteria. However, conditions like bowel obstructions, scar tissue adhesions, tumors, or surgeries (including gastric bypass) can impair this vital motility. When the small intestine's flow stagnates, bacteria are allowed to excessively multiply.
Impaired motility can also arise from underlying conditions affecting the nerves and muscles controlling digestion, such as hypothyroidism, gastroparesis, multiple sclerosis, Parkinson's disease, diabetes, and others. In these cases, the small intestine's flow grows sluggish, creating a low-motility environment where bacterial overgrowth can easily take hold.
Whether due to anatomical blockages or nerve/muscle disorders, anytime the small intestine loses its ability to maintain that efficient river-like flow and cleansing process, it sets the stage for SIBO to develop. Restoring proper motility is often key to reestablishing bacterial balance.
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Anatomical abnormalities
Structural changes in your GI tract, such as strictures (narrowing of parts of the intestine) or diverticula (small pouches that form on the inner intestinal wall), can create pockets where bacteria can multiply.
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Low stomach acid
Reduced stomach acid levels, often seen in conditions like H. pylori infection or certain acid-suppressing medications, can impair your body's ability to control bacterial growth by decreasing its ability to kill bacteria effectively.
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However, the evidence on acid-suppressing medications isn’t clear-cut, and not all medications in this drug class have the same impact. Research suggests proton pump inhibitors, which are stronger acid-suppressing drugs, aren’t likely to negatively affect acid levels in the small intestine and don’t contribute to bacterial overgrowth.
Other medications
Medications, such as narcotics used for pain management and anticholinergics used for urinary problems, can hinder gut function and promote bacterial overgrowth.
What are the risk factors for SIBO?
Several risk factors can make a person more susceptible to SIBO. They include:
Impaired immune function
The immune system plays a crucial role in regulating the bacterial population in the gut. People with immune deficiencies, autoimmune disorders affecting the GI tract, or conditions compromising immune function can impair the body's ability to control bacterial overgrowth in the small intestine.
Age and sex
While SIBO can occur at any age, it may be more common in adults ages 65 and older. Age-related changes in GI motility, reduced stomach acid production, and other health conditions may be the reason this group has an increased risk.
SIBO is also more likely to occur in females. Emerging research suggests a potential link between SIBO in women and autoimmune conditions, highlighting the interplay between gut health and immune function.
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GI conditions
Conditions that interfere with the normal function of the GI tract, such as IBS, celiac disease, and inflammatory bowel disease (IBD), are associated with an increased risk of SIBO. Inflammation or changes in gut motility may create an environment where bacteria can grow.
What are the types of SIBO?
SIBO can be classified based on the types of gases found in the body that aren’t readily produced by humans. Those gases indicate the presence of bacteria in the small intestine and include:
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hydrogen-dominant SIBO
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methane-dominant SIBO
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hydrogen sulfide-dominant SIBO
Hydrogen-dominant SIBO
Hydrogen-dominant SIBO is an overgrowth in the small intestine of bacteria such as E. coli and Klebsiella, which produce hydrogen gas. The excess hydrogen gas can be absorbed into the bloodstream and exhaled through the lungs, where it can be detected using a SIBO breath test. Hydrogen-dominant SIBO is also likely to cause symptoms similar to IBS with diarrhea and bloating.
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Methane-dominant “SIBO”
Methane-dominant SIBO is more accurately referred to as intestinal methanogen overgrowth (IMO) because the methane-producing microbes aren’t bacteria but single-celled organisms known as archaea.
In the case of IMO, certain species of archaea produce methane gas. The archaea most likely to contribute to IMO is called Methanobrevibacter smithii. But unlike hydrogen gas, methane isn’t readily absorbed into the bloodstream and tends to accumulate in the intestines. There, it can cause problems, such as slow gut motility and symptoms similar to IBS with constipation. Though methane isn't readily absorbed into the bloodstream, enough of it makes it to the lungs and still be detected by a breath test.
Hydrogen sulfide-dominant SIBO
In hydrogen sulfide-dominant SIBO, certain bacteria produce excess hydrogen sulfide gas. Hydrogen sulfide may play a role in relaxing smooth muscle and contributing to inflammation in your GI tract. Hydrogen sulfide-dominant SIBO may bring about symptoms similar to those of IBS with diarrhea. Additionally, a higher rate of hydrogen sulfide tends to correlate with more severe diarrhea.
How is SIBO diagnosed?
If you have ongoing digestive symptoms, SIBO may not be at the top of your healthcare provider's mind. That's because SIBO symptoms often overlap with many other digestive conditions such as IBS. Before your healthcare provider makes a diagnosis, they will review your symptoms and medical history. If they suspect SIBO, they will likely recommend a breath test to measure the gases produced by the microbes in your small intestine.
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What is the SIBO breath test?
Healthcare providers use breath testing to examine fermented gases produced by bacteria and archaea found in your breath when you exhale. Previous breath tests could only measure hydrogen and methane—two out of the three gases that cause symptoms. The previous lack of available testing for hydrogen sulfide allowed some people to slip through the cracks or receive a false negative result.
“It's estimated that up to 25% of patients who appear normal on hydrogen and methane tests could have elevated hydrogen sulfide levels and associated GI complications,” says Dr. Mark Pimentel, executive director of MAST.
But recent advancements in technology have led to an innovative 3-gas breath test for SIBO, capable of measuring all three primary fermented gases in the gut. A 3-gas breath test measuring hydrogen, methane, and hydrogen sulfide provides a more complete picture of your gut health than other tests.
Typically, a healthy gut contains some amount of hydrogen, methane, and hydrogen sulfide, but high levels on the 3-gas breath test can suggest bacterial overgrowth. The information from this test can also help your healthcare provider develop your treatment plan.
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Will I need other tests?
Besides a breath test, your healthcare provider may recommend additional tests, such as stool tests to assess microbial imbalances, blood tests to evaluate vitamin and mineral deficiencies, or other imaging to look at anatomical or structural changes.
How is SIBO treated?
Treating SIBO involves eradicating the overgrown bacteria in the small intestine, restoring gut health, and alleviating symptoms. Common SIBO treatments may include a combination of medications and dietary or lifestyle changes.
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Antibiotics for SIBO
Antibiotics are the most common treatment for SIBO. Your breath test will help determine which antibiotic will work best for your type of SIBO. Some of the antibiotics your healthcare provider may prescribe include:
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rifaximin
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amoxicillin/clavulanate
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ciprofloxacin
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metronidazole
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doxycycline
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neomycin
Rifaximin is often a first-line treatment for SIBO because most of it stays in the gut, isn’t absorbed by the rest of the body, has a low risk of antibiotic resistance, and has minimal side effects. Your healthcare provider may also prescribe different types of antibiotics and may adjust your treatment plan as needed. The length of time you may need to take antibiotics for SIBO may vary from 7-14 days.
However, some people can have recurring cases of bacterial overgrowth, requiring additional antibiotic therapy. Treating SIBO with antibiotics can sometimes be complicated because they disrupt the balance of bacteria in your digestive system, potentially worsening some symptoms, such as diarrhea and yeast overgrowth, you’re trying to alleviate.
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Other SIBO medications
Your healthcare provider may prescribe medications that promote GI motility, such as prucalopride, low-dose erythromycin, or low-dose naltrexone, to help prevent bacterial overgrowth.
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Dietary modifications
Adopting dietary changes may help to eliminate foods that increase symptoms or reduce fermentable carbohydrates that feed bacteria in the small intestine. Some of the diets your healthcare provider may discuss with you include:
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low fodmap
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elimination diet
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elemental diet
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specific carbohydrate diet
Additionally, your healthcare provider may recommend you take probiotics or prebiotics to restore a healthy balance of gut flora.
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Lifestyle changes
Beyond medications and dietary modifications, you may have certain nutritional deficiencies that need to be corrected. For example, a B12 deficiency can lead to fatigue, anemia, and problems with the nervous system. The inability to effectively absorb calcium can result in osteoporosis or kidney stones. Your healthcare provider may have you take certain supplements to replenish key nutrients to help you feel better. Some forms of nutritional support may come as a shot or intravenous (IV) fluid, while others may come as pills.
Some steps you can take on your own to help improve SIBO symptoms include managing stress, optimizing sleep, and incorporating regular physical activity. These can support overall gut health and reduce the risk of SIBO recurrence.
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Managing SIBO day in and day out is difficult, but advancements in research, testing methods, and treatment options offer a way forward for countless people who’ve been unable to find relief. From dietary modifications to more targeted therapies, getting your gut back on track and feeling better is possible.
SIBO FAQs
Can SIBO lead to other health problems?
Is SIBO contagious?
Can probiotics help with SIBO?
Can SIBO cause GERD?
Can SIBO cause weight loss or weight gain?
What is the best test for SIBO?
How long does it typically take to treat SIBO?
Can SIBO recur after treatment?
Will SIBO go away on its own?
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Sorathia SJ, Chippa V, Rivas JM. Small Intestinal Bacterial Overgrowth. 2023 Apr 17. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan–. PMID: 31536241.
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