Effects of dietary saturated and n-6 polyunsaturated fatty acids on the incorporation of long-chain n-3 polyunsaturated fatty acids into blood lipids

INTRODUCTION The consumption of saturated fatty acids (SFA) is often related to the development of chronic diseases, especially coronary heart disease (CHD) and other cardiovascular diseases (CVD), (1,2) despite conflicting [...]
BACKGROUND/OBJECTIVES: Omega-3 polyunsaturated fatty acids (n-3PUFA) are better absorbed when they are combined with high-fat meals. However, the role of different dietary fats in modulating the incorporation of n-3PUFA in blood lipids in humans has not been previously explored. Omega-6 polyunsaturated fatty acids (n-6PUFA) are known to compete with n-3PUFA in the metabolic pathways and for the incorporation into phospholipids, whereas saturated fats (SFA) may enhance n-3PUFA incorporation into tissues. SUBJECTS/METHODS: In a randomized parallel-design trial, we aimed to investigate the long-term effects of n-3PUFA supplementation in subjects consuming a diet enriched with either SFA or n-6PUFA on fatty acid incorporation into plasma and erythrocytes and on blood lipid profiles (total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and triglycerides). RESULTS: Dietary supplementation with n-3PUFA co-administered with SFA for 6 weeks resulted in a significant rise in total cholesterol (0.46 [+ or -] 0.60 mmol/L;P = 0.020) and LDL-C (0.48 [+ or -] 0.48 mmol/L;P = 0.011) in comparison with combination with n-6PUFA. The diet enriched with SFA also induced a greater increase in eicosapentaenoic acid (2.07 [+ or -] 0.79 vs 1.15 [+ or -] 0.53;P = 0.004), a smaller decrease in docosapentaenoic acid (-0.12 [+ or -] 0.23 vs - 0.30 [+ or -] 0.20;P =0.034) and a similar increase in docosahexaenoic acid (3.85 [+ or -] 1.14 vs 3.10 [+ or -] 1.07;P = 0.128) percentage in plasma compared with the diet enriched with n-6PUFA. A similar effect was seen in erythrocytes. N-3PUFA supplementation resulted in similar changes in HDL-C and triglyceride levels. CONCLUSIONS: The results suggest that dietary substitution of SFA with n-6PUFA, despite maintaining low levels of circulating cholesterol, hinders n-3PUFA incorporation into plasma and tissue lipids. European Journal of Clinical Nutrition (2016) 70, 812-818; doi: 10.1038/ejcn.2015.213; published online 13 January 2016