Benefits
LDL cholesterol, non-HDL cholesterol and apolipoprotein B
In a meta-analysis of 28 randomized trials (1,924 people), a median of about 10.2 g/day of psyllium lowered LDL cholesterol by 0.33 mmol/L (about 13 mg/dL), with lower non-HDL cholesterol and apolipoprotein B as well. An earlier pooled analysis of 8 trials found about 7% lower LDL when psyllium was added to a low-fat diet. HDL and triglycerides did not change.
Fasting blood sugar and HbA1c
A meta-analysis of 35 randomized studies found the effect tracks starting blood sugar: no significant change with normal glucose, a smaller improvement in prediabetes, and the largest drops in people treated for type 2 diabetes. Three of its five authors worked for Procter & Gamble. An independent analysis of 19 placebo-controlled trials also found lower fasting blood sugar, HbA1c and HOMA-IR, but not insulin.
Stool water, stool output and bowel movement frequency
In a 2-week double-blind trial in 170 adults with chronic constipation, 5.1 g of psyllium twice daily raised stool water content and total weekly stool output, and by the second week bowel movements were more frequent than in the comparison group, who took docusate (a stool softener). There was no placebo group, and the lead author worked for Procter & Gamble.
Digestive comfort and abdominal symptoms
In a 12-week primary care trial in 275 adults with irritable bowel syndrome, 10 g/day of psyllium gave adequate symptom relief to more people than placebo in the first two months and cut symptom severity scores more by month three. Quality of life did not differ. Bran did not beat placebo in a worst-case analysis.
Fullness and appetite between meals
In two placebo-controlled crossover studies in healthy adults, run with researchers from Procter & Gamble (maker of Metamucil), 6.8 g of psyllium before meals for 3 days reduced hunger and the desire to eat and increased fullness between meals. A meta-analysis of 22 randomized trials found no significant change in body weight, BMI or waist size; a 6-trial analysis in overweight adults by Procter & Gamble staff found about 2 kg lost.
Systolic blood pressure
A meta-analysis of 11 randomized trials (592 participants with high blood pressure) found that psyllium lowered systolic blood pressure by about 2 mmHg, with larger drops in people who started higher. No side effects were reported in the pooled trials.
Mechanism of action
Viscous gel formation
Psyllium forms a high-viscosity gel in the small intestine. Reviews of fiber research link this viscosity to the cholesterol and blood sugar effects: gel-forming fibers such as psyllium, beta-glucan and raw guar gum show them, while non-viscous fibers such as inulin and wheat dextrin do not.
Bile acid turnover and LDL cholesterol
In a randomized crossover study in 20 men with high cholesterol, 15 g/day of psyllium for 40 days lowered LDL cholesterol, reduced relative cholesterol absorption and sped up bile acid turnover. Bile acid synthesis rose in the men whose LDL fell by more than 10%, and the authors concluded that psyllium lowers LDL mainly by stimulating bile acid synthesis.
Water-holding gel in the colon
A review of fiber research explains that a laxative effect needs fiber that resists fermentation and stays largely intact through the large bowel. There, psyllium's water-holding gel resists drying out, which keeps stools bulky and soft. Fermentable soluble fibers such as inulin and wheat dextrin do not give this laxative effect.
Post-meal glucose, insulin and gut hormone responses
In a crossover study in 16 healthy young adults, fiber-enriched test meals, one with 23 g of psyllium, lowered post-meal glucose, insulin, ghrelin and PYY responses. GLP-1 rose at first after the psyllium meal, as after the other test meals, and was suppressed only after a meal high in both fiber and protein whose fiber source the abstract does not name. In a second study, 1.7 g of psyllium in pasta did not change GLP-1, glucose or insulin.
Clinical trials
Systematic review and meta-analysis of 28 randomized controlled trials lasting at least 3 weeks, in people with or without high cholesterol. (Jovanovski et al. 2018, Am J Clin Nutr)
1,924 participants pooled from 28 randomized trials.
A median dose of about 10.2 g/day of psyllium lowered LDL cholesterol by 0.33 mmol/L (about 13 mg/dL; 95% CI 0.27 to 0.38 mmol/L), non-HDL cholesterol by 0.39 mmol/L (about 15 mg/dL) and apolipoprotein B by 0.05 g/L versus control. The authors graded the LDL and non-HDL results as moderate quality, because results varied between trials, and the apolipoprotein B result as high quality.
Randomized placebo-controlled trial in general practice: 10 g psyllium (85 people), 10 g bran (97) or 10 g rice flour placebo (93) daily for 12 weeks. (Bijkerk et al. 2009, BMJ)
275 adults aged 18 to 65 with irritable bowel syndrome.
The primary outcome, adequate symptom relief, was reached by more people on psyllium than placebo in month one (57% vs 35%) and month two (59% vs 41%). After three months symptom severity fell by 90 points on psyllium versus 49 on placebo. Quality of life did not differ. Bran helped only in month three, and not in the worst-case analysis; bran users dropped out early most often, mainly because symptoms got worse. About a third of the psyllium group did not complete the 12 weeks.
Meta-analysis of 35 randomized controlled studies found through Scopus and Procter & Gamble clinical study records; three of the five authors, including the first author, worked for Procter & Gamble. (Gibb et al. 2015, Am J Clin Nutr)
Adults with normal glucose, adults at risk of type 2 diabetes, and adults being treated for type 2 diabetes.
In people being treated for type 2 diabetes, psyllium taken before meals lowered fasting glucose by 37.0 mg/dL and HbA1c by 0.97 percentage points. There was no significant glucose lowering in people with normal glucose, and the improvement in people at risk of type 2 diabetes was smaller.
Systematic review and meta-analysis of 19 randomized placebo-controlled trials found through PubMed, Web of Science and Scopus; funded by Isfahan University of Medical Sciences, and the authors declared no competing interests. (Gholami et al. 2024, BMC Endocr Disord)
962 adults pooled from 19 randomized trials.
Psyllium lowered fasting blood sugar, HbA1c (by 0.75 percentage points; 95% CI 0.29 to 1.21) and HOMA-IR (by 1.17) versus placebo, but the change in insulin was not significant. The fasting blood sugar effect was not significant in trials shorter than 50 days, and the HbA1c effect was not significant at intakes under 10 g/day.
Multicenter randomized double-blind parallel trial: a 2-week placebo baseline, then 2 weeks of psyllium 5.1 g twice daily or docusate sodium 100 mg twice daily, each with a placebo of the other; there was no placebo-only group, and the first author worked for Procter & Gamble. (McRorie et al. 1998, Aliment Pharmacol Ther)
170 adults with chronic idiopathic constipation.
Compared with docusate, psyllium raised stool water content (2.33% vs 0.01% change from baseline), stool water weight (84.0 vs 71.4 g per bowel movement) and total stool output (359.9 vs 271.9 g per week). Bowel movement frequency did not differ in week 1 (3.3 vs 3.1 per week) but was higher with psyllium in week 2 (3.5 vs 2.9 per week).
Two randomized, double-blind, placebo-controlled crossover studies of 3 days each: study 1 tested 3.4, 6.8 and 10.2 g before breakfast and lunch; study 2 tested 6.8 g with an energy-restricted breakfast. Adverse events were mostly mild digestive symptoms, at rates similar to placebo. Two of the four authors worked for Procter & Gamble. (Brum et al. 2016, Appetite)
Healthy volunteers; the abstract does not give the number enrolled.
In study 1, all three doses gave directional or significant drops in hunger and desire to eat and more fullness between meals versus placebo; 3.4 g was the weakest and 6.8 g gave the most consistent effect. In study 2, 6.8 g lowered 3-day mean hunger and desire to eat and raised fullness versus placebo.
Single-blind randomized crossover study of five test meals of equal energy: low fiber, 23 g psyllium fiber, high soy protein, high protein plus 23 g fiber (fiber source not named in the abstract), and white wheat bread. (Karhunen et al. 2010, J Nutr)
16 healthy, non-obese young adults.
The fiber-enriched meals lowered post-meal glucose, insulin, ghrelin and PYY responses, and PYY release lasted longer. GLP-1 rose at first after the other meals, including the psyllium meal, and was suppressed only after the meal high in both fiber and protein. Appetite ratings after the meals were mostly similar.
Randomized single-blind 2 x 2 crossover study: pasta with or without 1.7 g psyllium (an amount the abstract ties to the FDA health claim label), with or without 30 g sunflower oil and 3 g sodium propionate added to the meal; each meal had 50 g available carbohydrate. (Frost et al. 2003, Eur J Clin Nutr)
10 adults; the abstract does not describe their health status.
Psyllium had no significant effect on GLP-1, gastric emptying, glucose or insulin responses. Adding fat with sodium propionate raised GLP-1, delayed gastric emptying and lowered glucose.
Systematic review and dose-response meta-analysis of 22 randomized controlled trials. (Darooghegi Mofrad et al. 2020, Crit Rev Food Sci Nutr)
Adults in 22 randomized trials.
Psyllium did not significantly change body weight (mean difference -0.28 kg, 95% CI -0.78 to 0.21), BMI (-0.19 kg/m2) or waist circumference (-1.2 cm, 95% CI -2.6 to 0.2).
Systematic review and meta-analysis of 6 randomized controlled trials lasting at least 2 months, with psyllium dosed just before meals; all three authors were employees of Procter & Gamble, maker of Metamucil. (Gibb et al. 2023, J Am Assoc Nurse Pract)
354 overweight or obese adults; mean dose 10.8 g/day for a mean of 4.8 months.
Psyllium lowered body weight by 2.1 kg (95% CI 1.6 to 2.6), BMI by 0.8 kg/m2 and waist circumference by 2.2 cm versus control. This differs from a larger 22-trial analysis that found no significant change in weight, BMI or waist size.
Systematic review and meta-analysis of 11 randomized controlled trials. (Clark et al. 2020, Korean J Intern Med)
592 participants with high blood pressure.
Psyllium lowered systolic blood pressure by 2.04 mmHg on average, with larger drops in people who started with higher blood pressure. No side effects were reported.