Key Findings:
This a meta-analysis included twenty-eight studies and investigated whether flaxseed lignans can lower cholesterol and regress the atherosclerotic process. Problems with previous studies conducted with flaxseed include use of small sample size, insufficient study duration, variation in study designs, and diversity of the test product. Overall, reductions in blood total and LDL-cholesterol concentrations and no changes in HDL cholesterol and triglycerides were noted. Results varied due to the treatment form of flaxseed, quality of the study, sex, and initial lipid profile of the subjects. Whole flaxseed interventions were associated with significant reductions in total and LDL cholesterol, whereas flaxseed oil interventions were not. Flaxseed was more effective at reducing cholesterol in people with initial high initial cholesterol concentrations and more effective in women than in men. Postmenopausal women experienced the greatest cholesterol reduction effects. No significant effects of flaxseed or its derivatives on HDL cholesterol and triglycerides was noted. Unfortunately, the effects of flaxseed on lipid profiles were note homogenous because of the substantial variation among individual studies. Future studies should use large sampler sizes, adequate durations, and solid study designs. Despite this review, Health Canada approved a blood cholesterol lowering claim for whole milled flaxseed in 2014 recognizing the importance of flaxseed consumption to decrease CVD-related morbidity and mortality.
Abstract:
Several clinical trials have investigated the effects of flaxseed and flaxseed-derived products (flaxseed oil or lignans) on blood lipids; however, the findings have been inconsistent. We aimed to identify and quantify the effectiveness of flaxseed and its derivatives on blood lipid profiles. A comprehensive literature search was performed on the basis of English reports of randomized controlled trials of flaxseed or its derivatives on lipid profiles in adults, which were published from January 1990 to October 2008. Attempts also were made to access unpublished data. Study quality was assessed by using the Jadad score, and a meta-analysis was conducted. Twenty-eight studies were included. Flaxseed interventions reduced total and LDL cholesterol by 0.10 mmol/L (95% CI: 20.20, 0.00 mmol/L) and 0.08 mmol/L (95% CI: 20.16, 0.00 mmol/L), respectively; significant reductions were observed with whole flaxseed (20.21 and 20.16 mmol/L, respectively) and lignan (20.28 and 20.16 mmol/L, respectively) supplements but not with flaxseed oil. The cholesterol-lowering effects were more apparent in females (particularly postmenopausal women), individuals with high initial cholesterol concentrations, and studies with higher Jadad scores. No significant changes were found in the concentrations of HDL cholesterol and triglycerides. Flaxseed significantly reduced circulating total and LDL-cholesterol concentrations, but the changes were dependent on the type of intervention, sex, and initial lipid profiles of the subjects. Further studies are needed to determine the efficiency of flaxseed on lipid profiles in men and premenopausal women and to explore its potential benefits on other cardiometabolic risk factors and prevention of cardiovascular disease. (Author’s abstract)
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