The husk of seeds from plants of the Plantago genus, principally Plantago ovata, used as a source of soluble dietary fibre. Also known as psyllium husk, ispaghula swells dramatically in water to form a viscous gel, which is why it serves both as a food thickener and as a bulk-forming laxative. In baking, particularly gluten-free baking, it improves dough structure, moisture retention, and crumb texture. As a supplement it helps relieve constipation and can modestly lower blood cholesterol when taken regularly with plenty of fluid. Products containing ispaghula must carry warnings to take it with adequate water, since the dry husk can swell in the throat and cause choking if swallowed without liquid.