PHYTOSTEROLS PARTIALLY EXPLAIN DIFFERENCES IN CHOLESTEROL-METABOLISM CAUSED BY CORN OR OLIVE OIL FEEDING

To examine whether phytosterols in polyunsaturated oils account for th eir differential action on lipid metabolism compared with monounsatura ted oils, 16 normolipidemic individuals consumed three 10-day experime ntal diets containing corn oil (high in polyunsaturated fatty acids an d phytosterols), olive oil (high in monounsaturated fatty acids and lo w in phytosterols), or olive oil supplemented with phytosterols given at mice the level naturally found in corn oil (high in monounsaturated fatty acids and phytosterols). Plasma total cholesterol concentration s after both the olive oil and the olive oil-phytosterol treatments we re higher (P < 0.001) than those after the corn oil treatment, Olive o il treatment resulted in greater (P < 0.05) plasma LDL-cholesterol and triglyceride concentrations compared to corn oil treatment. Addition of the phytosterol mixture to the olive oil diet resulted in suppressi on of the significant differences in LDL-cholesterol and triglyceride concentrations between corn and olive oil. Free cholesterol fractional synthetic rates determined by deuterium incorporation were lower (P < 0.05) with olive oil treatment compared to corn oil treatment; the si gnificance of this difference was abolished with the addition of phyto sterols to the olive oil diet. These results suggest that phytosterols are partly responsible for the differences in plasma cholesterol leve ls and synthesis observed between polyunsaturated and monounsaturated oils.