Abstract
Raised plasma lipids are one the most important risk factors for cardiovascular disease. Flaxseed contains considerable amounts of α-linolenic acid, phenolic compounds, and lignans, which each have the capacity to reduce circulating lipid concentrations. This study aimed to systematically review current evidence to identify the potential effects of flaxseed supplementation on blood lipid profiles using a meta-analysis of randomized controlled trials (RCTs). PubMed, Scopus, Web of Science, and Google Scholar databases were searched for publications between January 1900 and May 2019. Weighted mean differences (WMDs) were analyzed using a random-effects model. The Cochrane Collaboration tool was also used to assess the risk of bias of the studies included. Sixty-two RCTs with a total of 3772 participants met the eligibility criteria. Our analysis showed that flaxseed supplementation significantly reduced total cholesterol (TC) (WMD = -5.389 mg/dL; 95% CI: -9.483, -1.295, p = 0.010), triglyceride (TG) (WMD = -9.422 mg/dL; 95% CI: -15.514, -3.330, p = 0.002), and low-density lipoprotein cholesterol (LDL-C) (WMD = -4.206 mg/dl; 95% CI: -7.260, -1.151, p = 0.007) concentrations. However, it had no effects on high-density lipoprotein cholesterol (WMD = 0.047 mg/dl; 95% CI: -0.777, 0.872, p = 0.910). This meta-analysis suggested that flaxseed supplementation improves serum TC, TG, and LDL-C, which could delay the progression of heart disease. Further studies with large-scale and better design are now needed to confirm these results.
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Key Points
Despite increased research on flaxseed, there are inconsistencies between trials examining effects on lipid profile, with some investigations showing beneficial effects, while others have not. The present meta-analysis showed that flaxseed products have a beneficial effect in subjects with disrupted baseline serum TG, TC and LDL-C. There were mixed findings regarding the duration of studies, which may depend on the mechanism of action of flaxseed, its bioactive components and the impact of other dietary ingredients. Flaxseed fed to subjects with an unhealthy metabolic status and/or disrupted baseline serum lipids have beneficial effects on their lipid profile. Future large, long duration, high-quality trials should be designed to ensure low risk of bias and to meet current reporting standards for clinical trials. Consuming flaxseed and its products (doses from 10.0 to 60.0 g per day) has a beneficial effect on lowering TC, LDL-C and TG in humans and could provide important an alternative strategy to control dyslipidemia and CVD.