Zhang W, Wang X, Liu Y, et al. Dietary flaxseed lignan extract lowers plasma cholesterol and glucose concentrations in hypercholesterolaemic subjects. Br J Nutr. 2008;99:1301-9.
Fifty-five individuals with high cholesterol participated in this randomized, double-blind, placebo-controlled study. Participants were given flaxseed-derived lignan extracts (300 or 600 mg/day) or placebo for 8 weeks after which fasting blood glucose levels and lipid profiles were determined. Subjects who received 600 mg of extract had reductions in total cholesterol, LDL, and fasting blood glucose levels. Although other studies have reported discrepant effects on cholesterol levels by flaxseed, the authors postulate that these inconsistencies are due at least in part to the variable quantity of lignan within whole or defatted flaxseeds, a complication that is overcome with use of an extract.
Pan A, Sun J, Chen Y, et al. Effects of a flaxseed-derived lignan supplement in type 2 diabetic patients: a randomized, double-blind, cross-over trial. PLoS ONE 2007; 2(11):e1148.
Effects of flaxseed-derived lignan supplementation in 68 type II diabetic participants were analyzed in this randomized, double-blind, cross-over study. After 12 weeks of receiving lignan supplements (360 mg/day) or placebo, the participants underwent an 8-week washout period before completing the remaining treatment arm. Glycemic control (as determined by HbA1c) was modestly affected by lignan supplementation; however, fasting glucose and insulin levels, insulin resistance, and blood lipid concentrations were unaltered. Because the influence of lignan on glycemic control was modest, additional studies are required to determine if it is clinically meaningful.
Brooks JD, et al. Supplementation with flaxseed alters estrogen metabolism in postmenopausal women to a greater extent than does supplementation with an equal amount of soy. Am J Clin Nutr 2004;79:318-25.
In this study, 46 postmenopausal women were randomized to receive a placebo, soy (25 g soy flour), or flaxseed (25 g ground flaxseed) muffin for 16 weeks. Blood and 24-h urine samples were analyzed at baseline and at the endpoint for estrogen metabolites, serum hormones, and biochemical markers of bone metabolism. Results showed that the urinary concentrations of 2-hydroxyestrone, but not of 16alpha-hydroxyestrone increased significantly in the flaxseed group. There was no effect on the biochemical markers of bone metabolism. But since the study was limited by a short treatment time and fewer subjects, long-term studies with larger treatment groups are warranted.