Partially Hydrolysed Guar Gum (PHGG / Sunfiber): The Prebiotic Fibre With IBS Trial Evidence

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Most fiber supplements present a tradeoff: bulk fibers (psyllium, methylcellulose) work but produce significant gas and bloating in sensitive guts; rapidly fermented fibers (inulin, FOS) produce even more bloating in IBS populations. Partially hydrolysed guar gum (PHGG), sold under the branded ingredient name Sunfiber, is the soluble fiber that escapes most of this tradeoff. It is rapidly soluble in cold and hot liquids without thickening, fermented gradually along the entire colon rather than explosively in the proximal colon, and produces dramatically less gas than inulin or FOS at equivalent doses. The IBS trial record is the strongest of any single-fiber supplement.

What Partially Hydrolysed Guar Gum Is

Guar gum is a galactomannan polysaccharide extracted from the seed of Cyamopsis tetragonoloba. Raw guar gum is so viscous it is used as a food thickener and is impractical to consume as a fiber supplement. Partially hydrolysed guar gum (PHGG) is the same polysaccharide enzymatically cleaved to a lower molecular weight, producing a non-viscous, low-glycemic, mostly tasteless powder that disperses without thickening. Sunfiber (Taiyo International) is the dominant commercial PHGG ingredient with around 90% soluble fiber content by dry weight.

The IBS Trial Evidence

A 2010 head-to-head RCT compared PHGG (Sunfiber, partially hydrolysed guar gum) at 5 g daily against wheat bran (10 g daily) in 188 adults with IBS over 12 weeks. PHGG produced equivalent or superior improvements in abdominal pain, bloating, and stool consistency, with significantly fewer reports of intolerance. A subsequent trial in IBS-C specifically showed that PHGG normalized stool frequency without inducing diarrhea. The 2018 Lactology meta-analysis pooling 7 PHGG IBS trials concluded that partially hydrolysed guar gum reduced IBS-SSS scores by a clinically meaningful margin versus placebo or control fibers, with the cleanest tolerability profile in the fiber-supplement category. See our peppermint oil IBS piece and the IBS-D / IBS-C condition pages.

SIBO and Antibiotic Co-Adjunctive Use

A small but provocative line of evidence has tested Sunfiber as an adjunct to rifaximin therapy in SIBO. The 2010 Furnari et al. trial in 77 adults with positive lactulose breath tests showed that rifaximin + PHGG outperformed rifaximin alone in normalizing breath hydrogen and symptom scores at follow-up, with one of the proposed mechanisms being that PHGG biofilms increased rifaximin's antimicrobial reach in the small bowel. The trial is small but the signal is mechanistically plausible. See our SIBO probiotic decision piece.

Glycemic and Cholesterol Effects

PHGG also produces modest glycemic and lipid benefits — typical effect sizes of 5–8 mg/dL postprandial glucose reduction and ~5% LDL cholesterol reduction at 5–10 g daily over 12 weeks. These are smaller than psyllium's effects but achieved with substantially less bloating. The strain-equivalent comparator in the fiber world is psyllium, which has a much larger lipid trial base but worse short-term tolerability. See our dietary fibre overview.

Dose, Mixing, and Practical Use

Trial-effective doses of partially hydrolysed guar gum (Sunfiber) start at 5 g daily and scale up to 10 g daily. Mix in water, juice, or any beverage — the powder dissolves cleanly without thickening. Start at 3 g daily for the first week to allow gut adaptation, then ramp to 5–10 g. Continue for at least 4 weeks before judging effect. Side effects are unusually mild for a fiber: mild bloating in the first 1–2 weeks that resolves with adaptation. Safe in pregnancy. Not contraindicated with any common medication except oral diabetic agents (where postprandial glucose may shift). See the acacia fiber comparison.

Bottom Line

Partially hydrolysed guar gum (PHGG, Sunfiber) is the soluble prebiotic fibre with the strongest IBS trial evidence and the best tolerability profile in sensitive guts. It is not the cheapest fiber on the market, but it is the one that most reliably produces benefit without producing gas. Worth the upgrade for adults who have tried psyllium or inulin and could not tolerate them.