Key Findings
This study assessed whether lignans from flaxseed may have a cholesterol-lowering effect. A randomized, double-blind, placebo-controlled, crossover study was conducted to determine whether a lignan complex isolated from flaxseed would affect endothelial function, inflammation markers, plasma lipids, and plasma antioxidant capacity in healthy postmenopausal women. The main objectives of the present study were to determine whether a lignan complex isolated from flaxseed would 1) increase serum ENL concentration and urinary ENL excretion, 2) reduce plasma lipid concentrations, 3) increase serum lipoprotein resistance to oxidation ex vivo, and 4) affect plasma antioxidant capacity. A high serum ENL concentration and urinary ENL excretion was found suggesting that SDG is highly available to the colonic microflora and that it was metabolized to ENL. In this study, 6 wk of consumption of a low-fat muffin enriched with a lignan complex, providing 500 mg/d of SDG, significantly increased serum ENL concentrations and urinary ENL excretion in healthy postmenopausal women, but had no effect on plasma lipid concentrations, serum lipoprotein oxidation resistance, or plasma antioxidant capacity. These results do not suggest that plant lignans isolated from flaxseed would affect plasma lipid concentration or antioxidant capacity in healthy postmenopausal women.
ABSTRACT
A lignan complex rich in the plant lignan secoisolariciresinol diglucoside (SDG) was isolated from flaxseed. SDG is metabolized by the colonic microflora to the mammalian lignans enterodiol (END) and enterolactone (ENL), and was hypothesized to reduce plasma lipid concentrations and improve antioxidant capacity. The aim of this study was to investigate the effects of a lignan complex, providing 500 mg/d of SDG, on serum concentration and urinary excretion of ENL, plasma lipids, serum lipoprotein oxidation resistance, and markers of antioxidant capacity. Healthy postmenopausal women (n = 22) completed a randomized, double-blind, placebo-controlled, crossover study. Women consumed daily a low-fat muffin, with or without a lignan complex, for 6 wk, separated by a 6-wk washout period. Serum ENL concentration, urinary ENL excretion, plasma concentrations of total cholesterol (TC), LDL cholesterol (LDL-C), HDL cholesterol (HDL-C), triacylglycerol (TAG), serum lipoprotein oxidation lag time, plasma Trolox-equivalent antioxidant capacity (TEAC), and ferric reducing ability of plasma (FRAP) were measured at the beginning and end of each intervention period. ENL concentrations in serum (P < 0.001) and ENL urinary excretion (P < 0.001) were significantly higher after the lignan complex intervention period compared with placebo. Plasma concentrations of TC, LDL-C, HDL-C, TAG, lipoprotein oxidation lag time, TEAC and FRAP were not affected. Daily consumption for 6 wk of a low-fat muffin enriched with a lignan complex significantly increased serum ENL concentrations and urinary ENL excretion in healthy postmenopausal women, but had no effect on plasma lipid concentrations, serum lipoprotein oxidation resistance, or plasma antioxidant capacity.