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

Objective: The aim of this meta-analysis was to investigate the effect of increasing dietary low-ratio n-6/n-3 polyunsaturated fatty acid (PUFA) intake on blood glucose and other related indicators. Methods: We systematically searched randomized controlled trials of low-ratio n-6/n-3 PUFA intervention on PubMed, Embase, Cochrane library and related references up to August 2018. The change values were calculated as the weighted mean difference (WMD) by using a random-effect model. Results: Eleven randomized controlled trials were included. No significant effect of dietary low-ratio n-6/n-3 PUFA supplementation was observed on fasting blood glucose (WMD: 0.057 mmol L-1; 95% CI: -0.090 to 0.204 mmol L-1), insulin (WMD: -0.757 mIU L-1; 95% CI: -2.419 to 0.904 mIU L-1), insulin resistance index (WMD: -0.201; 95% CI: -0.566 to 0.165), and glycosylated hemoglobin (WMD: -0.063%; 95% CI: -0.061 to 0.186%). Subgroup analysis showed that the effect of low-ratio n-6/n-3 PUFA on the reduction of the plasma insulin level in North America (WMD: -3.473 mIU L-1; 95% CI: -5.760 to -1.185 mIU L-1) was more obvious than that in Asian countries (WMD: -0.797 mIU L-1; 95% CI: -2.497 to 0.902 mIU L-1) and European countries (WMD: -0.063 mIU L-1; 95% CI: -0.061 to 0.186 mIU L-1). In the subgroup of diabetic subjects, low-ratio n-6/n-3 PUFA supplementation can decrease the plasma insulin level (WMD: -3.010 mIU L-1; 95% CI: -5.371 to -0.648 mIU L-1) and insulin resistance index (WMD: -0.460; 95% CI: -0.908 to -0.012). When the intervention period was longer than 8 weeks, low-ratio n-6/n-3 PUFA supplementation could also decrease the plasma insulin level (WMD: -2.782 mIU L-1; 95% CI: -4.946 to -0.618 mIU L-1). No significant publication bias was observed for all blood glucose and other related indicators as suggested by Begg's test and Egger's test. Conclusion: Our meta-analysis found that low-ratio n-6/n-3 PUFA supplementation could improve the glucose metabolism by reducing the insulin and insulin resistance in the diabetic patients. Low-ratio n-6/n-3 PUFA supplementation could reduce the plasma insulin level when the supplementation duration was longer than 8 weeks.