Psyllium encourages water resorption in the intestines, turning it into a gel that slows digestion, increases fecal weight, and improves stool consistency.[1][2] These qualities are what psyllium is best known for and likely explain its actions as a laxative and appetite suppressant.[3][4]
Compared to similar fibers, psyllium is less fermentable in the gut, which means it’s less likely to produce flatulence, stomach pain, and nausea.[3] Lower fermentability also means psyllium produces fewer short-chain fatty acids in the colon. However, notably, butyrate (a short-chain fatty acid) is produced after psyllium consumption (10 grams of husk twice per day), which could help prevent the growth of potentially pathogenic bacteria while improving mineral absorption.[5][6][7]
Other proposed mechanisms for psyllium’s reported actions include increased glucose uptake and fatty acid oxidation in skeletal muscle (for improved glucose regulation);[8][9] the release of satiety-promoting intestinal peptides, slowed gastric emptying, and regulation of the postmeal glycemic response (for appetite suppression);[10][4][11][12] and/or increased bile acid production (for cholesterol reductions).[13][14][15] However, it should be noted that much of this evidence is still preclinical (from animal and in vitro research), so these observed mechanisms may not necessarily translate into clinical effects.