Enhanced efficacy of sitostanol-containing versus sitostanol-free phytosterol mixtures in altering lipoprotein cholesterol levels and synthesis in rats.

To investigate the action and mechanism of a dietary phytosterol mixture naturally containing sitostanol, derived from tall-oil, on circulating cholesterol and lipoprotein levels, five groups of rats were fed a control elemental diet (group 1), a control elemental diet with 1% cholesterol alone (group 2) or with sitostanol mixtures or a sitostanol-free mixture supplemented at 0.2% (group 3), 0.5% (group 4) or 1% (group 5) of dietary levels. One per cent supplementation of sitostanol (21%) compared with sitostanol-free mixtures decreased (P < 0.02) total serum cholesterol. Dietary sitostanol (16% or 21%) mixture at 1% dietary levels decreased (P < 0.05) low density lipoprotein (LDL) cholesterol and increased (P < 0.05) high density lipoprotein (HDL) cholesterol levels. The decrease of LDL and increase of HDL cholesterol were correlated (P < 0.01) with the level of sitostanol mixture in the diet. Consumption of the sitostanol-containing mixture (1% dietary levels) caused a compensatory increase in cholesterol synthesis as indicated by elevated (P < 0.05) lathosterol/ cholesterol ratios in plasma and hepatic cholesterol fractional synthesis rate (FSR) (P < 0.02). Both sitostanol and sitostanol-free mixtures at 0.5% or 1% dietary intake levels increased plasma campesterol and beta-sitosterol levels, while plasma sitostanol levels were negligible. The absence of sitostanol in plasma and the increase in cholesterol synthesis induced by dietary sitostanol mixtures in addition to elevation of plasma campesterol and beta-sitosterol by sitostanol or sitostanol-free mixtures suggest that sitostanol mixtures effectively modify circulating lipoprotein cholesterol concentrations at the level of the intestine, rather than internally at the level of cholesterogenesis.