SIBO testing and treatment: what the research really shows

Small intestinal bacterial overgrowth, or SIBO, has gone from a niche diagnosis to a popular explanation for bloating. With easy access to hydrogen breath testing, it's now diagnosed in people with a wide range of symptoms, and it gets frequent attention in the media (Quigley et al., 2020).

For a woman who's tired of bloating every afternoon, a clear label and a course of antibiotics can sound like relief. The research, however, is more complicated. Here's what experts and studies say about what SIBO is, how it's tested and what treatment can realistically do.

A condition that's hard to define

SIBO is generally used to describe symptoms, signs or lab changes that are attributed to changes in the number or type of bacteria in the small intestine. Symptoms traditionally linked to it include bloating, diarrhea and abdominal pain or discomfort (Quigley et al., 2020).

But in its 2020 expert review, the American Gastroenterological Association described the definition of SIBO as lacking precision and consistency, and said its true prevalence is undefined. One major obstacle is how little is known about what a normal bacterial population in the small intestine looks like (Quigley et al., 2020).

What the research says about breath tests

Breath tests are the most common way to test for SIBO. You drink a sugar solution, usually glucose or lactulose, and your breath is sampled for hydrogen and methane. A North American consensus defined a positive test as a hydrogen rise of at least 20 parts per million within 90 minutes, and considered a methane level of at least 10 parts per million methane-positive (Rezaie et al., 2017).

The harder question is what a positive result means. A meta-analysis of 25 studies compared 3,192 people with IBS and 3,320 controls. With breath testing, SIBO was found in 35.5% of people with IBS, but also in 29.7% of the controls (Shah et al., 2020).

The type of breath test mattered a great deal. Lactulose tests found SIBO much more often than glucose tests: 3.6 times as often in people with IBS and 7.6 times as often in controls. The authors rated the overall quality of evidence as low, partly because of the limited sensitivity and specificity of the available tests (Shah et al., 2020).

Is SIBO behind IBS?

There does appear to be a link. In the same meta-analysis, people with IBS had 3.7 times the odds of SIBO compared with controls (Shah et al., 2020). But a link isn't the same as a cause.

The AGA review notes that SIBO's role in common symptoms, such as those of IBS, remains controversial. It adds that although IBS has been shown to respond to a poorly absorbed antibiotic, whether that response has anything to do with SIBO still needs confirmation in randomized trials (Quigley et al., 2020).

What treatment studies show

The antibiotic studied most often for SIBO is rifaximin. A meta-analysis of 32 studies with 1,331 patients found an overall eradication rate of 70.8%, with adverse events in 4.6%. In the 10 studies that reported it, symptoms improved or resolved in 67.7% of patients whose SIBO was eradicated (Gatta and Scarpignato, 2017).

Those numbers sound encouraging, but the authors described the quality of the available studies as generally poor. The AGA review also points out how little evidence exists to guide antibiotic strategies for SIBO, and urges caution about the risks of long-term broad-spectrum antibiotics (Gatta and Scarpignato, 2017; Quigley et al., 2020).

What about acid-reducing medications?

Proton pump inhibitors (PPIs) are often mentioned as a SIBO risk factor. A meta-analysis of 11 studies found higher odds of SIBO in PPI users, but only when SIBO was diagnosed with cultures of small intestine fluid, not with glucose breath tests (Lo and Chan, 2013). In people with IBS specifically, PPI use wasn't associated with SIBO in the 2020 meta-analysis (Shah et al., 2020).

When testing may make sense

Given this uncertainty, SIBO testing tends to be most useful when there's a specific reason to suspect it, rather than as a first step for everyday bloating. The AGA review emphasizes identifying and correcting underlying causes where possible and treating nutritional deficiencies, particularly in people with significant maldigestion or malabsorption (Quigley et al., 2020).

Questions worth asking your doctor:

• Is there a reason I might be at higher risk, such as past bowel surgery or a condition that slows my gut?
• Which breath test would you use, and how would a positive result change my treatment?
• Have we ruled out other causes, such as celiac disease, constipation or medication side effects?
• If I'm treated and my symptoms come back, what's the plan?

And don't let a SIBO label distract from red flags. Weight loss, anemia, blood in your stool, persistent diarrhea or symptoms that wake you at night need a full medical evaluation.

Sources

1. Quigley EMM, Murray JA, Pimentel M. AGA clinical practice update on small intestinal bacterial overgrowth: expert review. Gastroenterology. 2020;159(4):1526-1532. PMID 32679220
2. Rezaie A, Buresi M, Lembo A, et al. Hydrogen and methane-based breath testing in gastrointestinal disorders: the North American consensus. Am J Gastroenterol. 2017;112(5):775-784. PMID 28323273
3. Shah A, Talley NJ, Jones M, et al. Small intestinal bacterial overgrowth in irritable bowel syndrome: a systematic review and meta-analysis of case-control studies. Am J Gastroenterol. 2020;115(2):190-201. PMID 31913194
4. Gatta L, Scarpignato C. Systematic review with meta-analysis: rifaximin is effective and safe for the treatment of small intestine bacterial overgrowth. Aliment Pharmacol Ther. 2017;45(5):604-616. PMID 28078798
5. Lo WK, Chan WW. Proton pump inhibitor use and the risk of small intestinal bacterial overgrowth: a meta-analysis. Clin Gastroenterol Hepatol. 2013;11(5):483-90. PMID 23270866

This article is for general information and isn't medical advice. Don't take antibiotics or start a restrictive diet for suspected SIBO without guidance from your healthcare provider.