The strongest evidence stands for constipation relief through increased water resorption, which increases fecal weight and improves stool consistency.[1][2][3][4][5][6] As a function of its partial fermentability and gel-forming properties, psyllium is thought to promote beneficial changes to the gut microbiota in people with constipation, but so far this has only been seen when psyllium is combined with other dietary fibers.[7]
Those same gel-forming properties may also be responsible for the reductions in serum glucose concentrations and HbA1c levels that are sometimes seen when psyllium is used by people with type 2 diabetes.[8][9][10][11][8][12]
Psyllium has shown potential for other digestive health and metabolic health measures as well. Use of psyllium has been associated with sustained remission in people with ulcerative colitis and reduced symptoms of gastroesophageal reflux disease.[13][14] When taken with or prior to a meal, psyllium may produce small reductions in body mass measurements for people with higher BMIs.[15][16][17] However, body composition changes may be more of a result of appetite suppression.[18][19][20][21][22][12][20][21][22]
For improvements in cardiovascular conditions, psyllium’s effects are most consistent when used for LDL cholesterol reduction. Still, some studies have shown promise for improvements in other blood lipid measures and blood pressure as well.[23][24][25][26][27][28][8][29][30] However, it does seem that there is a lot of variation in the studies themselves, so further research is needed to determine effective ranges for dose, duration, timing, and frequency of psyllium use.[31][28][32][27][8][33][34][30][35][36][37][23][24][38][26]