Psyllium

Psyllium is the husk of seeds from Plantago ovata, a shrub native to the Indian subcontinent. It's the active ingredient in Metamucil and many generic fiber supplements, and unusual in that it works at both ends of bowel-function problems: it relieves constipation by adding bulk and water, and it firms loose stools by absorbing excess fluid. The same gel-forming property does both.

Compared to other fiber supplements (wheat dextrin, inulin, methylcellulose), psyllium has the strongest evidence base for cholesterol reduction, glycemic control, and IBS symptom improvement — and it's well tolerated by most people, including those on low-FODMAP diets where many fibers cause problems.

How psyllium works

Psyllium is about 70% soluble fiber, forming a viscous gel in the gut. The gel slows gastric emptying, slows glucose absorption (lowering post-meal blood sugar), binds bile acids (lowering LDL cholesterol — typically a 5–10% reduction at 10g/day), and adds bulk and moisture to stool. Unlike most prebiotic fibers, psyllium is only minimally fermented by gut bacteria, which is why it produces less gas and bloating than inulin or wheat bran.

Practical use

Typical doses: 5–10g once or twice daily, mixed into a large glass of water and drunk immediately before it gels in the glass. Drink additional water through the day — psyllium without enough fluid can actually worsen constipation or cause obstruction. Start with a smaller dose and ramp up over a week. Take it separately from medications (at least an hour apart), since the gel can reduce drug absorption. For IBS, multiple trials show psyllium reduces overall symptom severity; for diabetes and prediabetes, it modestly lowers HbA1c and post-meal glucose.