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Research · Supplements

Fiber supplements

Psyllium lowered LDL cholesterol by 0.33 mmol/L across 28 trials. Fiber raised response rates in chronic constipation, mainly psyllium above 10 g a day. Soluble fiber reduced persistent IBS symptoms and bran did not. Weight findings conflict, with 2.5 kg loss on soluble fiber and a gain in a psyllium pooling. More flatulence. Rare esophageal obstruction and allergy.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement in the US. Psyllium is also sold as an over-the-counter bulk laxative.
Also called
psyllium, psyllium husk, ispaghula, Plantago ovata, Metamucil, glucomannan, konjac, inulin, pectin, methylcellulose, wheat dextrin, soluble fiber
Taken for
constipation, regularity, cholesterol, blood sugar, weight loss, fullness, IBS, gut health

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help4

Reported risks3

What people take it for, and what was found

Shown to help4

Strong

LDL cholesterol

Shown to lower LDL cholesterol by about 0.33 mmol/L with about 10 g of psyllium a day in adults with or without high cholesterol.

The numbers and sources
Effect
Across 28 trials (1,924 participants), a median 10.2 g of psyllium a day lowered LDL cholesterol by 0.33 mmol/L (95% CI -0.38 to -0.27), non-HDL cholesterol by 0.39 mmol/L and apoB by 0.05 g/L (95% CI -0.08 to -0.03) [1]. A 2025 meta-analysis of 41 RCTs (2,049 participants) found LDL cholesterol 8.55 mg/dL lower (95% CI -12.92 to -4.19) and total cholesterol 9.05 mg/dL lower. Triglycerides and HDL did not change significantly [2].
Population
Adults with or without high cholesterol in RCTs of 3 weeks or longer [1]; adults in 41 RCTs [2].
Sources
[1], [2]
Caveats
LDL and non-HDL estimates were graded moderate quality because of inconsistency, and apoB high quality [1]. Heterogeneity in the 2025 review was considerable (I² 88% for LDL), and dose and duration did not explain it [2].
ModerateVery common

Chronic constipation

Shown to help more adults with chronic constipation, 66% against 41% on control, mostly at more than 10 g a day.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
Across 16 RCTs (1,251 adults), 66% responded to fiber and 41% to control (RR 1.48, 95% CI 1.17 to 1.88, I² 57%). Fiber raised stool frequency (SMD 0.72, 95% CI 0.36 to 1.08, I² 86%) and improved stool consistency (SMD 0.32). Psyllium and pectin had significant effects, and response was higher only above 10 g a day [3].
Population
Adults with chronic constipation [3].
Sources
[3]
Caveats
Heterogeneity was considerable. The stool frequency gain appeared only at higher doses and at 4 weeks or more [3].
Moderate

Irritable bowel syndrome

Shown to lower persistent IBS symptoms in adults, with soluble fiber helping one extra person for every 7 treated. Bran did not differ from control.

The numbers and sources
Effect
Across 14 RCTs (906 patients), fiber lowered the risk of persistent IBS symptoms (RR 0.86, 95% CI 0.80 to 0.94, number needed to treat 10). Soluble fiber showed RR 0.83 (95% CI 0.73 to 0.94, number needed to treat 7), and bran did not differ from control (RR 0.90, 95% CI 0.79 to 1.03) [4].
Population
Adults with IBS [4].
Sources
[4]
Caveats
No significant heterogeneity, but the search ended in December 2013.
Limited

Blood sugar

Limited evidence: psyllium lowered fasting glucose and HbA1c in type 2 diabetes but not in normal blood sugar. Other fiber results were small or inconsistent.

The numbers and sources
Effect
In people treated for type 2 diabetes, psyllium taken before meals lowered fasting glucose by 37.0 mg/dL and HbA1c by 0.97%. There was no glucose lowering in people with normal blood sugar and a modest effect in prediabetes [5]. Across 12 RCTs in overweight and obese adults, isolated soluble fiber lowered fasting glucose by 0.17 mmol/L (95% CI -0.28 to -0.06) and fasting insulin by 15.88 pmol/L [6]. A 2026 meta-analysis of 11 glucomannan trials in adults with insulin resistance-related conditions found fasting glucose 7.02 mg/dL lower (95% CI -13.56 to -0.49), an effect that lost significance under an alternative correlation assumption [7]. In a 4-week trial of 131 adults, inulin lowered 1-hour and 2-hour glucose on a glucose tolerance test in overweight or obese participants but not in healthy-weight ones, and fructooligosaccharides did not change glucose in either group [8].
Population
35 psyllium RCTs across three groups [5]; 609 overweight and obese adults [6]; 11 glucomannan trials [7]; 131 adults in China [8].
Sources
[5], [6], [7], [8]
Caveats
Reference [5] searched clinical records held by Procter & Gamble, a psyllium supplement maker, as well as published studies, and its abstract does not report confidence intervals. The glucomannan result was not robust to the analysis method [7]. In the inulin trial, fasting insulin rose [8].

Mixed results1

Limited

Body weight

Limited evidence: soluble fiber lowered weight about 2.5 kg in overweight adults over short trials, while a glucomannan review found no change and a psyllium review reported a gain.

The numbers and sources
Effect
Across 12 RCTs (609 overweight and obese adults) lasting 2 to 17 weeks without calorie restriction, isolated soluble fiber reduced body weight by 2.52 kg (95% CI -4.25 to -0.79), BMI by 0.84 and body fat by 0.41% [6]. Across 11 glucomannan trials, obesity indices did not change significantly [7]. A 2025 meta-analysis of 27 psyllium RCTs in adults reported a significant increase in body weight (weighted mean difference 3.57, 95% CI 1.43 to 5.72) with no change in BMI (-0.06, 95% CI -0.68 to 0.55) or waist circumference [9].
Population
Overweight and obese adults [6]; adults with insulin resistance-related conditions [7]; adults in psyllium RCTs [9].
Sources
[6], [7], [9]
Caveats
Considerable heterogeneity for most outcomes, and short trials [6]. The psyllium review runs opposite in direction to the soluble fiber review, its abstract does not state the unit of the weight estimate, and its BMI estimate did not move with the weight estimate [9].

Doses studied

Cholesterol trials used a median 10.2 g of psyllium a day [1]. In constipation, response was higher above 10 g a day and stool frequency rose at 4 weeks or more [3]. Psyllium glycemic trials dosed before meals [5]. Weight trials ran 2 to 17 weeks [6]. In the glucomannan meta-analysis, subgroup drops in systolic pressure and LDL appeared above 3,000 mg a day or at 4 weeks or less [7].

Risks

Reported risks3

ModerateHow often is not known

Flatulence and bloating

Shown to raise flatulence over control in adults with chronic constipation.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Flatulence was higher with fiber than control (SMD 0.80, 95% CI 0.47 to 1.13) [3].
Population
Adults with chronic constipation [3].
Sources
[3]
Caveats
One meta-analysis reported this outcome in a pooled form.
LimitedHow often is not known

Esophageal obstruction

Case reports: a woman with an esophageal web had her esophagus blocked after taking a glucomannan diet aid.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
A 37-year-old woman developed delayed esophageal obstruction after an over-the-counter glucomannan diet aid and cleared it by vomiting before endoscopy. She was later found to have an esophageal web. The report lists gastrointestinal obstruction and changed absorption of other medicines among reported effects of glucomannan [10].
Population
One case report [10].
Sources
[10]
Caveats
A single case in a person with existing esophageal disease.
LimitedHow often is not known

Allergy and anaphylaxis to psyllium

Case reports: a woman died of anaphylaxis after taking a psyllium product. Workers who handle psyllium can become sensitized.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
A 42-year-old woman died of anaphylaxis after ingesting a psyllium product. The literature review describes sensitization in health care workers and pharmaceutical plant workers who handle psyllium, and a link between atopy and psyllium allergy [11].
Population
One fatal case and a literature review [11].
Sources
[11]
Caveats
The review does not give a rate in people taking psyllium.

Claims tested and not found

  1. That wheat bran eases IBS symptoms. Bran did not differ from control (RR 0.90, 95% CI 0.79 to 1.03) [4].
  2. That psyllium lowers blood sugar in people with normal glucose. No significant glucose lowering was observed in euglycemic subjects [5].

Sources

  1. Jovanovski E, Yashpal S, Komishon A, et al. Effect of psyllium (Plantago ovata) fiber on LDL cholesterol and alternative lipid targets, non-HDL cholesterol and apolipoprotein B: a systematic review and meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition. 2018. https://doi.org/10.1093/ajcn/nqy115
  2. Gholami Z, Paknahad Z. Psyllium supplementation and lipid profiles: systematic review and dose-response meta-analysis of randomized controlled trials. Genes & Nutrition. 2025. https://doi.org/10.1186/s12263-025-00786-5
  3. van der Schoot A, Drysdale C, Whelan K, et al. The Effect of Fiber Supplementation on Chronic Constipation in Adults: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials. American Journal of Clinical Nutrition. 2022. https://doi.org/10.1093/ajcn/nqac184
  4. Moayyedi P, Quigley EMM, Lacy BE, et al. The Effect of Fiber Supplementation on Irritable Bowel Syndrome: A Systematic Review and Meta-analysis. American Journal of Gastroenterology. 2014. https://doi.org/10.1038/ajg.2014.195
  5. Gibb RD, McRorie JW, Russell DA, et al. Psyllium fiber improves glycemic control proportional to loss of glycemic control: a meta-analysis of data in euglycemic subjects, patients at risk of type 2 diabetes mellitus, and patients being treated for type 2 diabetes mellitus. American Journal of Clinical Nutrition. 2015. https://doi.org/10.3945/ajcn.115.106989
  6. Thompson SV, Hannon BA, An R, et al. Effects of isolated soluble fiber supplementation on body weight, glycemia, and insulinemia in adults with overweight and obesity: a systematic review and meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition. 2017. https://doi.org/10.3945/ajcn.117.163246
  7. Jazinaki MS, Rafiei H, Bahari H, et al. Effects of Glucomannan on Cardiometabolic Parameters in Adults With Insulin Resistance-Related Conditions: A Systematic Review and Dose-Response Meta-Analysis. Food Science & Nutrition. 2026. https://doi.org/10.1002/fsn3.72460
  8. Li J, Liu F, Luo Y, et al. Differential effects of inulin and fructooligosaccharides on gut microbiota composition and glycemic metabolism in overweight/obese and healthy individuals: a randomized, double-blind clinical trial. BMC Medicine. 2025. https://doi.org/10.1186/s12916-025-04189-6
  9. Gholami Z, Paknahad Z. The effect of psyllium consumption on anthropometric indices: a systematic review and dose-response meta-analysis of randomized controlled trials. Journal of Health, Population and Nutrition. 2025. https://doi.org/10.1186/s41043-025-01103-x
  10. Vanderbeek PB, Fasano C, O'Malley G, et al. Esophageal obstruction from a hygroscopic pharmacobezoar containing glucomannan. Clinical Toxicology. 2007. https://doi.org/10.1080/15563650601006215
  11. Khalili B, Bardana EJ, Yunginger JW. Psyllium-associated anaphylaxis and death: a case report and review of the literature. Annals of Allergy, Asthma & Immunology. 2003. https://doi.org/10.1016/S1081-1206(10)61538-4

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