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

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Most fibre supplements involve a trade-off. Bulk fibres such as psyllium and methylcellulose work but can produce gas and bloating in sensitive guts, and rapidly fermented fibres such as inulin and fructo-oligosaccharides tend to provoke even more bloating in people with irritable bowel syndrome (IBS). Partially hydrolysed guar gum (PHGG), sold most prominently under the branded ingredient name Sunfiber, is a soluble fibre that is fermented gradually and dissolves into liquids without thickening. It has a small but reasonably consistent set of controlled trials in IBS, and — importantly — its tolerability in those trials has been good. It is one of the better-studied single fibres for IBS, though "best evidence among fibres" is a low bar: the trials are mostly small and several were conducted or funded by the ingredient's manufacturer.

What partially hydrolysed guar gum is

Guar gum is a galactomannan polysaccharide from the seed of Cyamopsis tetragonoloba. Raw guar gum is so viscous it is used as a food thickener and is impractical to swallow as a supplement. PHGG is the same polysaccharide enzymatically cleaved to a lower molecular weight, yielding a non-viscous, largely tasteless powder that disperses in water without gelling. Sunfiber (Taiyo) is the dominant commercial PHGG ingredient, marketed as roughly 90% soluble fibre by dry weight. Because it is fermented relatively slowly and completely, it generates fewer of the rapid gas peaks associated with inulin or FOS — the property that makes it attractive in sensitive guts.

The IBS trial evidence

The most-cited comparative trial is not from 2010 but from 2002: an Italian multicentre, randomized open-label study in 188 adults with IBS that compared PHGG 5 g/day against wheat bran 30 g/day over 12 weeks. Both improved abdominal pain and bowel habit with no significant difference between them on per-protocol analysis, but on intention-to-treat the PHGG group had a higher success rate (60% vs 40%), and far more patients voluntarily switched from bran to PHGG (about 50%) than the reverse (about 11%) — a tolerability and preference signal rather than a hard efficacy win. A later dose-comparison trial (10 g vs 5 g/day for 12 weeks) found symptom and quality-of-life gains at both doses that faded after treatment stopped, suggesting any benefit requires ongoing intake.

The cleanest placebo-controlled data come from a double-blind trial in 121 IBS patients randomized to PHGG 6 g/day or placebo for 12 weeks. PHGG significantly improved bloating scores versus placebo, with the effect persisting four weeks after the last dose; it did not significantly change overall IBS severity or quality-of-life scores. A separate double-blind randomized trial in 60 children with functional abdominal pain or IBS reported symptom improvement in 43% on PHGG versus 5% on placebo. And a manufacturer-affiliated randomized trial in 44 adults with loose-stool-predominant ("IBS-D-like") symptoms found PHGG normalized stool form on the Bristol scale without changing stool frequency. Across these studies the consistent finding is modest benefit for bloating and stool form, not a transformation of IBS — and the most relevant outcome (global symptom severity) was often unchanged. See our peppermint oil IBS piece and the IBS-D / IBS-C condition pages.

SIBO: a real adjunct signal

One genuinely interesting result sits outside the IBS literature. A 2010 randomized trial in 77 adults with small intestinal bacterial overgrowth (SIBO) confirmed by glucose hydrogen breath testing found that adding PHGG 5 g/day to the antibiotic rifaximin (1,200 mg/day for 10 days) raised eradication rates from 62% with rifaximin alone to 87% (per-protocol; 85% on intention-to-treat). The proposed mechanism is that the fibre improves small-bowel motility and clearance, helping the antibiotic work — not any direct antibacterial or "biofilm" effect. It is a single small trial, but it is a properly randomized one and the effect was statistically significant. See our SIBO probiotic decision piece.

What about glucose and cholesterol?

PHGG is a soluble, viscous-precursor fibre, and as a class such fibres can produce modest reductions in post-meal glucose and LDL cholesterol. The dedicated IBS and SIBO trials above were not designed to measure those endpoints, however, and we have not cited a specific effect size here because the high-quality metabolic data for PHGG specifically are limited. Psyllium has a much larger and more consistent lipid-lowering trial base; if cholesterol reduction is the primary goal, it — not PHGG — is the better-evidenced choice. See our dietary fibre overview.

Dose, mixing, and practical use

Trial-effective doses of PHGG in IBS ranged from about 5 to 10 g/day, and the SIBO adjunct trial used 5 g/day. The powder dissolves cleanly in water, juice, or other beverages without thickening. A sensible approach is to start low (around 3 g/day) for the first week to allow gut adaptation, then build to 5–10 g/day, and to continue for at least four weeks before judging the effect. Tolerability in the trials was good, with transient mild bloating the main complaint. As with any fibre, take it with adequate fluid; if you take medications that require precise timing or have diabetes managed with glucose-lowering drugs, discuss the addition with your clinician, since soluble fibre can blunt post-meal glucose and slightly alter the absorption of co-ingested drugs. A note on the evidence base: several PHGG/Sunfiber trials were sponsored or co-authored by the ingredient manufacturer, so independent replication would strengthen confidence. See the acacia fibre comparison.

Sources

1. Parisi GC, Zilli M, Miani MP, et al. "High-fiber diet supplementation in patients with irritable bowel syndrome (IBS): a multicenter, randomized, open trial comparison between wheat bran diet and partially hydrolyzed guar gum (PHGG)." Digestive Diseases and Sciences, 2002;47(8):1697-1704. PMID 12184518.
2. Parisi G, Bottona E, Carrara M, et al. "Treatment effects of partially hydrolyzed guar gum on symptoms and quality of life of patients with irritable bowel syndrome. A multicenter randomized open trial." Digestive Diseases and Sciences, 2005;50(6):1107-1112. PMID 15986863.
3. Niv E, Halak A, Tiommny E, et al. "Randomized clinical study: Partially hydrolyzed guar gum (PHGG) versus placebo in the treatment of patients with irritable bowel syndrome." Nutrition & Metabolism, 2016;13:10. PMID 26855665.
4. Romano C, Comito D, Famiani A, et al. "Partially hydrolyzed guar gum in pediatric functional abdominal pain." World Journal of Gastroenterology, 2013;19(2):235-240. PMID 23345946.
5. Yasukawa Z, Inoue R, Ozeki M, et al. "Effect of Repeated Consumption of Partially Hydrolyzed Guar Gum on Fecal Characteristics and Gut Microbiota: A Randomized, Double-Blind, Placebo-Controlled, and Parallel-Group Clinical Trial." Nutrients, 2019;11(9):2170. PMID 31509971.
6. Furnari M, Parodi A, Gemignani L, et al. "Clinical trial: the combination of rifaximin with partially hydrolysed guar gum is more effective than rifaximin alone in eradicating small intestinal bacterial overgrowth." Alimentary Pharmacology & Therapeutics, 2010;32(8):1000-1006. PMID 20937045.
7. Wierzbicka A, Khaidakov B, Zakerska-Banaszak O, et al. "Effects of a polyphenol-rich extract blend, probiotics, and hydrolyzed fiber on quality of life and gut health markers in patients with irritable bowel syndrome—A randomized, double-blind, placebo-controlled trial." Frontiers in Nutrition, 2025;12:1603011. PMID 40693198.