Psyllium is the common word used to refer to fibers taken from the plant known as Plantago ovata (Plantago psyllium is used synonymously, and is where the fiber name is derived from); the fiber is characterized by being water soluble (hydrophilic) and gel forming, while possessing low fermentability. It is commonly known by the brand name Metamucil.
Psyllium is used clinically as a bulk laxative, an agent that has laxative effects but secondary to increasing fecal size; a gentler laxative relative to chemical agents like caffeine or senna alexandrina. This bulk occurs due to water and gas absorption in the small intestines and colon to give chyme (made from digested food) more size and softness. This bulk is retained in the colon despite microflora as psyllium is poorly fermented (highly fermented fibers may be metabolized by bacteria in the colon, and water retaining properties with the fiber would be lost in this scenario).
Psyllium is proven to increase fecal size and moisture, and the most common characteristics of stool following supplementation of psyllium are 'soft, sleek, and easily passable.' Relative to other sources of dietary fiber, psyllium appears to be more effective at forming feces and appears to be one of the few fiber sources not associated with excessive flatulence.
Beyond the fecal properties, psyllium appears to be able to reduce total cholesterol and LDL cholesterol in persons with high cholesterol (secondary to the gel forming properties leeching bile acids, and cholesterol being used up to replace hepatic bile acids) and there is a slight reduction of HDL as well. This is common to all dietary fibers and is not unique to psyllium.
There appears to be some glucose reducing properties associated with psyllium supplementation that may benefit diabetics. These are not overly potent, but appear reliable as long as psyllium is taken; cessation of psyllium usage is associated with a loss of the glucose reduction, and this may be common to all soluble dietary fibers rather than just psyllium.
Psyllium may reduce appetite slightly when taken in high doses, but does not appear to be potent or reliable; long term studies using psyllium in the doses for fecal management have failed to find weight reducing properties of psyllium suggesting it is not a good weight management intervention.
