Phytosterols partially explain differences in cholesterol metabolism caused by corn or olive oil feeding

To examine whether phytosterols in polyunsaturated oils account for their differential action on lipid metabolism compared with monounsaturated oils, 16 normolipidemic individuals consumed three 10-day experimental diets containing corn oil (high in polyunsaturated fatty acids and phytosterols), olive oil (high in monounsaturated fatty acids and low in phytosterols), or olive oil supplemented with phytosterols given at twice the level naturally found in corn oil (high in monounsaturated fatty acids and phytosterols). Plasma total cholesterol concentrations after both the olive oil and the olive oil-phytosterol treatments were higher (P < 0.001) than those after the corn oil treatment. Olive oil 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 suppression 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 significance of this difference was abolished with the addition of phytosterols to the olive oil diet. These results suggest that phytosterols are partly responsible for the differences in plasma cholesterol levels and synthesis observed between polyunsaturated and monounsaturated oils.