Flaxseed and Cardiovascular Risk Factors: Results from a Double Blind, Randomized Controlled Clinical Trial.

Key Findings:

A randomized controlled trial (RCT) was conducted to evaluate whether 40 g ground flaxseed provided in baked products could reduce LDL-C and favorably affect markers of cardiovascular disease risk in hypercholesterolemic patients following a low fat, low cholesterol diet. Measurements were made of F2-isoprostanes, a validated in vivo marker of oxidative stress. The milled flaxseed initially reduced LDL-C, but effects were not sustained at 10 weeks. Flaxseed reduced HDL-C in men, but not women. The flaxseed improved insulin sensitivity, but did not affect markers of inflammation or oxidative stress. Longer clinical trials of 6–12 months duration which include a larger number of both men and women are needed to fully assess the potential of flax as a component of a healthy cardioprotective diet.

ABSTRACT:

Objective: Flaxseed is a rich source of alpha linolenic acid (ALA), fiber and lignans, making it a potentially attractive functional food for modulating cardiovascular risk. We studied the effects of flaxseed on markers of cardiovascular risk in hypercholesterolemic adults. Methods: Sixty-two men and post-menopausal women with pre-study low density lipoprotein cholesterol (LDL-C) between 130 and 200 mg/dl were randomized to 40g/day of ground flaxseed-containing baked products or matching wheat bran products for 10 weeks while following a low fat, low cholesterol diet. Fasting lipoproteins, measures of insulin resistance, inflammation, oxidative stress, and safety were assessed at 0, 5 and 10 weeks. Results: Flaxseed was well-tolerated, and increased serum levels of ALA (p < 0.001). Compared to wheat, flaxseed significantly reduced LDL-C at 5 weeks (-13%, p <0.005), but not at 10 weeks (<7%, p= 0.07).  Flaxseed reduced lipoprotein a (Lp[a]) by a net of 14% (p= 0.02), and reduced the homeostatic model assessment of insulin resistance (HOMA-IR) index by 23.7% (p= 0.03) compared to wheat at 10 weeks, but did not affect markers of inflammation (IL-6, Hs-CRP) or oxidative stress (ox LDL, urinary isoprostanes) at any time points. In men, flaxseed reduced HDL-C concentrations by a net of 16% (p = 0.03) and 9% (p =0.05) at 5 and 10 weeks, respectively. Conclusions: Ground flaxseed has a modest but short lived LDL-C lowering effect, yet reduces Lp(a) and improves insulin sensitivity in hyperlipidemic adults. The HDL-C lowering effect of flaxseed in men warrants additional study.