Effect of low-ratio n-6/n-3 PUFA on blood lipid level: a meta-analysis

Purpose The aim of this meta-analysis was to evaluate the effects of low-ratio n-6/n-3 PUFA on blood lipid levels. Methods We searched the PubMed, Embase, and Cochrane Library databases for randomized controlled trials of n-6/n-3 PUFA interventions up to March 2019. The change values were calculated as weighted mean differences (WMDs) by using a random-effect model. Subgroup analysis and meta-regression were used to explore the source of heterogeneity. Results A total of 30 randomized controlled trials with 1368 participants were identified. Compared with control, low-ratio n-6/n-3 PUFA significantly reduced triglyceride (TG) concentration (WMD: − 0.079 mmol/L, 95% confidence interval (CI): − 0.148 mmol/L to − 0.009 mmol/L, p = 0.026) and increased high-density lipoprotein cholesterol (HDL-C) concentration (WMD: 0.033 mmol/L, 95% CI: 0.007 to 0.058 mmol/L, p = 0.012). Subgroup analysis revealed that the effects of low-ratio n-6/n-3 PUFA on blood lipid levels were better for a longer time. The effects of α-linolenic acid on total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) concentrations were more obvious among participants. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) had more significant effects on TG and HDL-C concentrations. No significant publication bias was observed for TG and HDL-C, as suggested by the results of Begg’s test and Egger’s test. Conclusion Low-ratio n-6/n-3 PUFA significantly reduced TG concentration and increased HDL-C concentration. The beneficial effects of low-ratio n-6/n-3 PUFA on TG, TC, HDL-C, and LDL-C concentrations were enhanced with time. However, n-3 PUFA derived from plants significantly reduced TC and LDL-C concentrations, and n-3 PUFA derived from EPA and DHA significantly reduced TG concentration and increased HDL-C concentration.