A psyllium fiber supplement, often from psyllium husk, is a popular soluble fiber source that forms a gel in water, aiding digestion, promoting regularity (constipation/diarrhea relief), lowering cholesterol, managing blood sugar, and supporting heart and gut health by acting as a prebiotic. Available in powders (like Metamucil) and capsules, it's taken with plenty of water to bulk stool, create fullness, and support overall metabolic and digestive wellness.