Effects of high-fat and low-fat diets rich in monounsaturated fatty acids on serum lipids, LDL size and indices of lipid peroxidation in healthy non-obese men and women when consumed under controlled conditions.

objectiveTo study the effects of the dietary fat content on cardiovascular disease risk factors in humans when the fatty acid composition and types of carbohydrates are kept constant.

methodsA controlled dietary study in healthy volunteers with 2 dietary groups and a parallel design consisting of 2 dietary periods was conducted. First, participants received a 2-week wash-in diet rich in saturated fatty acids (SFA; 47% of total fatty acids) and were then randomly assigned to either a high-fat (40% of energy) or a low-fat diet (29% of energy) for 4 weeks. Both diets were isocaloric, rich in monounsaturated fatty acids (MUFA; 51% of total fatty acids) and had similar fatty acid and carbohydrate compositions.

resultsCompared to the wash-in diet, the high-fat and low-fat diets significantly lowered LDL-cholesterol (-0.34 and -0.41 mmol/l, respectively; P < 0.001 for time effect in RM-ANOVA), and HDL-cholesterol (-0.13 and -0.18 mmol/l, respectively; P < 0.001 for time), without any differences between the high-fat and low-fat diets (P = 0.112 and P = 0.085 for time × group interaction in RM-ANOVA, respectively). The size of the major LDL fraction, the LDL susceptibility to oxidation and the plasma concentrations of oxidized LDL (ox-LDL) were significantly reduced by both the high-fat and low-fat diet, again without significant differences between the diets. The ratio of ox-LDL/LDL-cholesterol, serum triacylglycerols and urinary F2-isoprostanes were not significantly affected by the diets.

conclusionA high-fat and a low-fat diet, both rich in MUFA, had similar effects on lipid-related cardiovascular disease risk factors in metabolically healthy men and women.