Synergistic effects of psyllium in the dietary treatment of hypercholesterolemia. We investigated psyllium fiber supplementation as a means of enhancing the cholesterol-lowering effect of the phase I American Heart Association diet. Fifty-nine subjects with total serum cholesterol (TC) levels ranging from 5.56 to 10.24 mmol/L (215 to 396 mg/dL) were given a 2-month dietary lead-in followed by 3 months of diet only (29 subjects) or diet supplemented with 20.4 g of psyllium daily (30 subjects). Unlike women, men had a significant decrease in levels of both TC (-8.0%) and low-density lipoprotein cholesterol (LDL-C) (-10.1%) during the dietary lead-in. Psyllium supplementation resulted in an additional 5.5% reduction in the TC levels as compared to diet alone. Psyllium supplementation combined with dietary lead-in resulted in an overall 17.3% decrease in the TC and a 20.0% decrease in LDL-C for men, with decreases of 7.7% and 11.6%, respectively, for women. Psyllium effectively enhances the cholesterol-lowering effect of the phase I diet. 