We evaluated the influence of sex and hormonal status on the effect of psyllium (PSY) supplementation on parameters of plasma lipoprotein metabolism. Twenty-four men, 23 premenopausal women, and 21 postmenopausal women (PMW) were randomly assigned to a fiber supplement (15 g PSY/d) or a control, provided via cookies, in a crossover design. Plasma lipids, insulin, apoprotein (apo) B, apo CI, apo CIII, and apo E concentrations and the composition and size of low-density lipoprotein (LDL) and very-low-density lipoprotein (VLDL) particles were measured at the end of each 30-day treatment period. Compared with control, PSY intake decreased plasma LDL cholesterol by an average of 8% (P <.0001) in men and pre- and PMW. There was a fiber-sex/hormonal status interaction on plasma triglycerides (TG) in the response to the intervention. Men had a 17% decrease in TG, while PMW had a 16% increase with PSY (P <.01). Plasma levels of apo C III, apo E, and insulin followed the same pattern as plasma TG with PSY consumption and decreased by an average of 12% in men (P <.05), but increased by 10% in PMW (P <.05). These reductions in apoproteins suggest an increased peripheral removal of TG in men, perhaps due to decreased insulin resistance, while in PMW, the increases in apoproteins may be related to an enhanced VLDL production. The lack of effect of PSY on VLDL metabolism in premenopausal women could be associated with the protective effect of estrogen. No prominent changes in VLDL and LDL composition were observed with PSY intake other than an increase in LDL phospholipid (P <.05). In addition, compared with men and PMW, the amount of TG per VLDL particle was less, and VLDL diameter was smaller in premenopausal women (P <.05). These results indicate an important role of sex and hormonal status in determining the effects of PSY on lipoprotein metabolism. Copyright 2002, Elsevier Science (USA). All rights reserved.