Treating SIBO with prebiotics

In short: the best-studied prebiotic in SIBO is partially hydrolyzed guar gum (PHGG). In a 2010 randomized trial, adding 5 g a day of PHGG to rifaximinRifaximin An antibiotic that is barely absorbed into the bloodstream, so it acts mainly inside the gut. It is a common prescription treatment for SIBO. raised the clearance rate from 62% to 85%². Other prebiotics have not been tested in SIBO itself. Rapidly fermented ones such as inulin, FOS and GOS are FODMAPsFODMAPs Fermentable oligo-, di- and monosaccharides and polyols: short-chain carbohydrates that are poorly absorbed and quickly fermented by gut microbes. that can worsen gas and bloating⁵, while gentler fibers such as acacia gum feed beneficial colon bacteria with few side effects in healthy people⁴.

A prebiotic is “a substrate that is selectively utilized by host microorganisms conferring a health benefit”¹: a food for beneficial gut bacteria, usually a type of fiber. Because fiber is food for bacteria, people with SIBO are often unsure whether prebiotics will help or make things worse. The answer depends on the fiber and the timing.

Why the type of fiber matters

Fibers differ in how quickly bacteria ferment them. Short-chain fibers such as inulin, fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS) are FODMAPs: they are fermented quickly and can cause gas and bloating in sensitive people⁵. With an overgrowth in the small intestine, more of that fermentation can happen early in the gut, where gas causes the most discomfort. Longer, more complex fibers such as acacia gum tend to be fermented more gradually and are often better tolerated⁴.

Partially hydrolyzed guar gum (PHGG)

PHGG is guar gum, from the guar bean, that has been partly broken down with enzymes so that it dissolves in water without forming a thick gel. Reviews describe beneficial effects on both constipation and diarrhea and on the gut microbiota, although much of the evidence is still preliminary³.

PHGG is the only prebiotic tested in a randomized SIBO trial. In the 2010 study, 77 people with SIBO took rifaximin 1,200 mg a day for 10 days, either alone or with 5 g of PHGG a day²:

• SIBO cleared in 62% of those on rifaximin alone.
• SIBO cleared in 85% (intention-to-treat) to 87% (per-protocol) of those on rifaximin plus PHGG.
• Symptoms improved in most of those who cleared, in both groups.

The researchers chose PHGG because it affects gut motility; why it boosts the antibiotic’s effect is not fully understood. See our guide to SIBO antibiotics.

Acacia gum (gum arabic)

Acacia gum is the dried sap of acacia trees. In a 2008 study, healthy volunteers took different daily amounts for 4 weeks. Acacia raised levels of Bifidobacteria and Lactobacilli in stool, with an optimal dose of about 10 g a day, at least as effectively as inulin and without significant side effects⁴. It has not been tested in people with SIBO. Practitioners often use it after treatment to rebuild the microbiome because it is generally well tolerated.

Human milk oligosaccharides (HMOs)

HMOs are sugars found in breast milk, now made for supplements. The most common is 2’-fucosyllactose (2’-FL). In a 2020 open-label trial of 317 adults with IBS, 5 g a day of 2’-FL and a second HMO (lacto-N-neotetraose) for 12 weeks improved stool consistency, IBS symptom scores and quality of life. The most common side effects were mild gas, abdominal pain and distension. There was no placebo group, and the study did not test for SIBO⁶.

Inulin, FOS and GOS

Inulin and FOS are found in chicory root, garlic, onions and wheat; GOS in legumes. All are FODMAPs and are usually limited during the low-FODMAP phase of a SIBO diet⁵.

In healthy people they are well tolerated at modest doses. In a 2009 crossover trial of 84 healthy volunteers, inulin-type fibers at 5 to 20 g a day caused only mild increases in digestive symptoms, which were significant only at 20 g a day⁷. In a 2015 trial in 29 healthy adults, 5 to 7.5 g of agave inulin a day for 3 weeks increased Bifidobacterium in stool three- to four-fold and reduced Desulfovibrio, a sulfide-producing bacterium, by 40%⁸. Whether these fibers help or hurt people with active SIBO has not been studied.

LactuloseLactulose A synthetic sugar the body cannot digest or absorb. As a breath-test substrate it travels the whole small intestine, which also makes false positives more likely., the sugar used in SIBO breath tests, also acts as a prebiotic at very low doses⁹, but it is rapidly fermented and generally avoided as a daily supplement in active SIBO.

Comparison

How practitioners time prebiotics

There are no trials comparing different prebiotic plans in SIBO. A common approach is:

1. During treatment: limit FODMAP fibers to control symptoms, and consider PHGG alongside antibiotics, the one combination with trial evidence².
2. After treatment: introduce gentle fibers such as PHGG or acacia in small, gradually increasing amounts.
3. Long term: reintroduce a wide variety of fiber-rich foods as tolerated, because long-term restriction reduces the fiber that colon bacteria need. Our low-FODMAP guide explains the reintroduction phase.

Prebiotics do not prevent relapse on their own. In a 2008 study, 44% of people had SIBO again within 9 months of successful antibiotic treatment¹⁰, which is why relapse prevention focuses on the root causes and on gut motility. For probiotics, see our probiotics guide.

Common questions

Is fiber bad for SIBO?

Not in general. Rapidly fermented FODMAP fibers can worsen symptoms during active SIBO⁵, but at least one fiber, PHGG, improved treatment results in a trial², and colon bacteria need fiber in the long term.

How much PHGG should I take?

The SIBO trial used 5 g a day for 10 days, taken alongside rifaximin². Start low if you are sensitive to fiber, and talk to your clinician about how it fits your treatment.