Replacement of dietary saturated fatty acids by trans fatty acids lowers serum HDL cholesterol and impairs endothelial function in healthy men and women

We tested whether trans fatty acids and saturated fatty acids had different effects on flow-mediated vasodilation (FMD), a risk marker of coronary hea rt disease (CHD). Consumption of trans fatty acids is related to increased risk of CHD, probably through effects on lipoproteins. Trans fatty acids di ffer from most saturated fatty acids because they decrease serum high-densi ty lipoprotein (HDL) cholesterol, and this may increase the risk of CHD. We fed 29 volunteers 2 controlled diets in a 2X4-week randomized crossover de sign. The "Trans-diet" contained 9.2 energy percent of trans fatty acids; t hese were replaced by saturated fatty acids in the "Sat-diet." Mean serum H DL cholesterol after the Trans-diet was 0.39 mmol/L (14.8 mg/dL), or 21% lo wer than after the Sat-diet (95% CI 0.28 to 0.50 mmol/L). Serum low density lipoprotein and triglyceride concentrations were stable. FMD+SD was 4.4 +/ -2.3% after the Trans-diet and 6.2 +/-3.0% after the Sat-diet (difference - 1.8%, 95% CI -3.2 to -0.4). Replacement of dietary saturated fatty acids by trans fatty acids impaired FMD of the brachial artery, which suggests incr eased risk of CHD. Further studies are needed to test whether the decrease in serum HDL cholesterol caused the impairment of FMD.