Trans monounsaturated fatty acids and saturated fatty acids have similar effects on postprandial flow-mediated vasodilation

OBJECTIVE: Several studies suggest that a fatty meal impairs flow-mediated vasodilation (FMD), a measure of endothelial function. We tested whether the impairment was greater for trans fats than for saturated fats. We did this because we previously showed that replacement of saturated fats by trans fats in a controlled diet decreased FMD after 4 weeks. DESIGN: We fed 21 healthy men two different test meals with 0.9-1.0 g fat/kg body weight in random order: one rich in saturated fatty acids (Sat), mainly from palm kernel fat, and one rich in trans fatty acids (Trans) from partially hydrogenated soy bean oil. The study was performed in our metabolic ward. We had complete data for both diets of 21 men. RESULTS: FMD increased from a fasting value of 2.3+/-2.0% of the baseline diameter to 3.0+/-1.7% after the Sat test meal (95% CI for change -0.33, 1.70) and from 2.7+/-2.3 to 3.1+/-2.0% after the Trans test meal (95% CI for change -0.57, 1.29). The increase after the Sat meal was 0.22 (-1.18-1.61) FMD% higher than after the Trans meal. Serum triacylglycerols increased by 0.46+/-0.36 mmol/l after the Sat test meal and by 0.68+/-0.59 mmol/l after the Trans test meal; a difference of 0.23 (0.07, 0.39) mmol/l. Serum HDL-cholesterol was hardly affected by the test meals. The activity of serum paraoxonase, an esterase bound to HDL, increased slightly after the two test meals but the difference between meals was not significant. CONCLUSION: FMD was not impaired and not different after test meals with saturated or trans fatty acids. Thus, differences in long-term effects of these fats are not caused by differences in acute effects on the vascular wall.