Benefits
Bowel regularity
In adults with chronic constipation, 4 weeks of daily PHGG shortened colon transit time and increased weekly bowel movements, with less straining and less laxative use, but that study had no placebo group. In a placebo-controlled trial in 52 long-term care residents, 5 g/day did not change bowel frequency or stool form, though laxative use fell.
Less bloating and gas
In a 12-week double-blind trial in 121 adults with IBS, 6 g/day reduced diary bloating and gas scores versus placebo, an effect that lasted 4 weeks after stopping. It did not change abdominal pain, stool frequency, overall symptom severity or quality of life.
Normal stool form in adults prone to loose stools
In a 12-week placebo-controlled trial in 44 healthy adults who tended toward loose stools, 5 g/day moved stool form toward the middle of the Bristol scale without changing how often people went. The fiber's maker funded the trial, helped write the protocol and supplied the product.
Prebiotic support for gut bacteria and butyrate
PHGG raised the share of Bifidobacterium in stool versus placebo in one 12-week trial. In a 3-week study in 20 healthy adults without a placebo group, 5 to 15 g/day raised stool butyrate and acetate and shifted several bacterial groups, and most changes faded once people stopped.
Easier to stay on than wheat bran
In an open-label trial in 188 adults with IBS, both 5 g/day of PHGG and 30 g/day of wheat bran improved pain and bowel habits after 12 weeks. About half of the bran group chose to switch to PHGG, versus about 1 in 10 the other way, and in the intention-to-treat analysis success was 60% with PHGG versus 40% with bran. There was no placebo group.
Blood sugar markers
In a 6-week trial in 44 adults with type 2 diabetes, adding 10 g/day lowered HbA1c slightly versus their own baseline, while fasting glucose did not change. Native guar slows the rise in blood sugar after a meal because it is thick; in an older glucose-test study that effect disappeared with non-viscous hydrolysed guar.
Mechanism of action
Shorter chains, low thickness
Enzymes cut guar gum's long galactomannan chains into shorter pieces, so PHGG dissolves without forming a gel. That makes it easy to drink and avoids the swelling that made native guar tablets risky, but it also removes most of the thickness behind native guar's effect on blood sugar.
Fermented by colon bacteria
PHGG is not digested in the small intestine. In the colon, bacteria break it down into short-chain fatty acids such as butyrate and acetate; in one study none of a 15 g daily dose was found intact in stool.
Little effect on nutrient absorption
In a small crossover study in healthy men on a liquid diet, PHGG did not appear to change the absorption of glucose, amino acids or fat, or insulin release, consistent with its low viscosity.
Clinical trials
Randomized, double-blind, placebo-controlled trial with a 2-week run-in, 12 weeks of PHGG (Sunfiber, 3 g/day for the first week, then 6 g/day) or maltodextrin placebo, and 4 weeks of follow-up; funded by two companies, Pro Natura and Sunwic AB, which did not design or run the study (Niv et al. 2016, Nutr Metab (Lond))
121 adults with irritable bowel syndrome randomized in Israel; 108 included in the analysis (49 PHGG, 59 placebo).
PHGG improved diary bloating scores and combined bloating and gas scores versus placebo, and the effect lasted at least 4 weeks after stopping. There was no effect on abdominal pain, stool frequency, the overall IBS severity score or quality of life. Dropouts were higher on placebo (49% vs 22%).
Multicenter, randomized, open-label trial of PHGG 5 g/day versus wheat bran 30 g/day for 12 weeks, with an option to switch groups after 4 weeks (Parisi et al. 2002, Dig Dis Sci)
188 adults with IBS (139 women, 49 men) at Italian centers, including diarrhea-predominant, constipation-predominant and alternating types.
Both fibers improved abdominal pain and bowel habits, with no difference in the per-protocol analysis. In the intention-to-treat analysis success was 60% with PHGG versus 40% with bran, and 49.9% switched from bran to PHGG versus 10.9% the other way. No placebo group, and patients knew what they were taking.
Prospective single-group study: 2-week run-in, then daily PHGG for 4 weeks, with transit-time testing before and after; the abstract states the dose as 5 mg daily, apparently meaning grams (Polymeros et al. 2014, Dig Dis Sci)
49 adults meeting Rome III criteria for chronic constipation in Greece; 39 completed.
Colonic transit time fell from about 57 to 46 hours, more in slow-transit patients. Weekly bowel movements rose, and straining, laxative days and pain days fell, with better stool form. With no placebo group, some of the change may reflect time and expectation.
Randomized, single-blinded, parallel-group trial of 5 g/day PHGG in 200 ml water versus 200 ml water alone for 4 weeks; residents kept their usual as-needed laxatives (Chan et al. 2022, J Nutr Health Aging)
52 residents of four long-term care facilities in Hong Kong with chronic constipation, average age about 84.
Bowel frequency and stool form did not differ between groups, so the main bowel outcomes were not improved. Use of lactulose, senna and total laxatives was significantly lower in the PHGG group in weeks 3 and 4. Adverse effects did not differ.
Randomized, double-blind, placebo-controlled, parallel-group trial of 5 g/day PHGG (Sunfiber) versus maltodextrin for 12 weeks plus a 4-week washout; the maker funded the study, supplied the product and employed three of the authors (Yasukawa et al. 2019, Nutrients)
44 healthy Japanese adults aged 20 to 49 with a tendency toward loose stools (at least 7 bowel movements a week, over half rated 5 or 6 on the Bristol scale).
PHGG moved Bristol stool scores toward normal compared with placebo and increased the share of Bifidobacterium in stool. Stool frequency did not change.
9-week single-group study with a 3-week lead-in, 3 weeks of PHGG stepped up from 5 to 10 to 15 g/day, and a 3-week washout; no placebo group; product supplied by Nestlé Austria (Reider et al. 2020, Nutrients)
20 healthy volunteers in Austria (19 completed; average age about 28).
Stool frequency and consistency changed during PHGG, mainly in men. Stool butyrate and acetate rose, Ruminococcus, Faecalibacterium and others increased, and species evenness fell. Most effects disappeared after stopping.
Randomized controlled trial of usual diet plus 10 g/day PHGG versus usual diet alone for 6 weeks (Dall'Alba et al. 2013, Br J Nutr)
44 adults with type 2 diabetes and metabolic syndrome in Brazil (23 in the PHGG group).
In the PHGG group, HbA1c fell from 6.88% to 6.57% and waist size from 103.5 to 102.3 cm compared with baseline; the control group lost a little weight. Fasting glucose, blood pressure, triglycerides, HDL, total and LDL cholesterol did not change in either group.