Effects of dietary monounsaturated fatty acids on lipoprotein concentrations, compositions, and subfraction distributions and on VLDL apolipoprotein B kinetics: dose-dependent effects on LDL

Background: Replacing dietary saturated fatty acids (SFAs) with monounsaturated fatty acids (MUFAs) lowers LDL cholesterol, but the underlying mechanisms remain unclear. Objective: We assessed the effects of replacing dietary SFAs with MUFAs on concentrations and subclass distributions of VLDL, intermediate-density lipoprotein, LDL, and HDL and on VLDL apolipoprotein B kinetics. Design: Thirty-five moderately hypercholesterolemic, middle-aged volunteers consumed for 6 wk, in random order, diets containing low (L-MUFA; 7.8% of energy from MUFAs), moderate (M-MUFA; 10.3% from MUFAs), or high (H-MUFA; 13.7% from MUFAs) amounts of MUFAs. Fasting blood samples were taken from all subjects after each intervention. VLDL apolipoprotein B kinetic studies were performed in a subgroup after the L-MUFA and H-MUFA diets. Results: Plasma cholesterol concentrations decreased in a dose-dependent manner with increasing intakes of dietary MUFAs. This change was entirely accounted for by reduced LDL cholesterol (-0.20 and -0.49 mmol/L after the M-MUFA and H-MUFA diets, respectively, compared with the concentration after the L-MUFA diet; P for trend < 0.01). Plasma triacylglycerol and HDL cholesterol were not significantly affected by the dietary intervention, nor were the concentrations of [VLDL.sub.1] ([S.sub.f] 60-400), [VLDL.sub.2] ([S.sub.f] 20-60), or intermediate-density lipoprotein ([S.sub.f] 12-20). Production and catabolic rates for [VLDL.sub.1] and [VLDL.sub.2] were also unaffected. HDL and LDL subclass distributions were not significantly altered, but as a consequence of the overall LDL lowering, concentrations of atherogenic LDL-III were 25% lower after the H-MUFA diet than after the L-MUFA diet (P = 0.02). Conclusion: The effects of replacing dietary SFAs with MUFAs on lipoprotein metabolism appear to be almost exclusively limited to the LDL density class. KEY WORDS Monounsaturated fatty acids, saturated fatty acids, LDL, VLDL, lipoprotein subfractions, cholesterol