Short answer: They work differently. Psyllium is a gel-forming fiber that is not fermented and has an FDA-authorized heart claim at 7 g of its soluble fiber a day.12 Inulin is a prebiotic that gut bacteria ferment; it raised bifidobacteria and helped bowel function in trials.34 We found no trial comparing them.
| Psyllium | Inulin | |
|---|---|---|
| Fiber type | Soluble, gel-forming, not fermented1 | Prebiotic carbohydrate gut microbes use as fuel3 |
| FDA heart claim | Yes: 7 g or more a day of soluble fiber from psyllium husk2 | No claim in the sources checked |
| Cholesterol | LDL down 0.33 mmol/L across 28 trials (median about 10.2 g a day)5 | Not covered in the sources checked |
| Blood sugar | In type 2 diabetes: fasting glucose down 37 mg/dL, HbA1c down 0.97%; no lowering with normal blood sugar1 | Not covered in the sources checked |
| Constipation | Used as a bulk laxative | 5 trials (252 people): more frequent, softer stools; no help for pain or bloating6 |
| Gut bacteria | Not the aim | Raised bifidobacteria at 3 to 20 g a day (50 studies)4 |
Psyllium forms a gel and is not fermented, which is why it is studied for cholesterol and blood sugar. A 2018 meta-analysis of 28 trials found it lowered LDL cholesterol, non-HDL cholesterol and apoB.5 A 2015 analysis found the blood sugar effect grew with how high blood sugar was to start: none in people with normal levels, the most in people treated for type 2 diabetes. That analysis drew on Procter & Gamble records, which makes Metamucil.1
Inulin is a prebiotic, food for gut bacteria, not a probiotic.3 A 2023 meta-analysis of 50 studies found chicory inulin-type fructans raised bifidobacteria and improved bowel function in healthy people; two of its authors work for a chicory inulin maker.4
These are study protocols, not personalized advice; confirm any dosing with your prescriber.
If you take a diabetes or cholesterol medicine, tell your prescriber before adding psyllium, since it can lower both. Neither replaces a prescribed treatment.
More detail: Probiotics vs prebiotics: what is the difference?, and the Psyllium Husk Fiber and Inulin guides.