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
Given the current lack of robust evidence based research, the current study was conducted to investigate the effects of flaxseed and flaxseed-derived products supplementation on specific adhesion molecules and inflammatory cytokines in adults through a meta-analysis. All randomized controlled trials (RCTs) on this topic were included. The present meta-analysis included additional randomized trials as well other markers (CRP (n=35), TNF-α (n=17), IL-6 (n=16), I-CAM (n=7), V-CAM (n=6), E-selectin (n=5)) and found indicated that supplementation significantly decreased CRP, IL-6, and VCAM-1. With respect to CRP, this was only affected in RCTs with unhealthy or overweight participants in trials administered whole flaxseed and lignan supplement or for>12 weeks for<12 weeks or flaxseed oil.
The present meta-analysis strengths were evaluating dose–responses for the first time, together with subgroup analysis and assessment of the impact of baseline BMI, the participants health, study duration, and type of supplement on the overall effect sizes. In addition, methods for analyzing depended on between-group’s mean changes that are more accurate than within-group changes, thereby enabling to assess greater effect sizes. In addition, the study minimized any biases in the review process by performing a comprehensive search of the literature and also by adhering to the PRISMA guidelines.
The meta-analysis strongly suggested that giving flaxseed supplements to subjects that are overweight and/or with an unhealthy metabolic status could have beneficial effects. Furthermore, flaxseed is considered as an alternative source of marine-derived omega-3 fatty acid due to it’s readily availability and it is inexpensive compare to fish oil.