Flaxseed: A Source of Hypocholesterolemic and Antiatherogenic Agents

Recently there has been a moderate resurgence in the use of flaxseed food. However, the scientific basis of the benefits of flaxseed consumption and which components of flaxseed offer these beneficial effects are not known. Flaxseed contains 32-45% of its mass as oil, of which 51-55% is alpha-linolenic acid (n-3 fatty acids, omega-3 fatty acids). Flaxseed lignan (secoisolariciresinol diglucoside; SDG) is isolated from defatted flaxseed. Flaxseed has been shown to have variable effects on plasma lipids. Serum triglycerides (TG), total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) have been reported to be elevated, lowered or unchanged with flaxseed consumption in rats. In humans, flaxseed lowers serum TC and LDL-C; however, it has no effect on serum high-density lipoprotein-cholesterol (HDL-C) and TG. Flaxseed oil also lowers TG and TC in rats, but the effect is smaller than that of flaxseed. Flaxseed oil in human subjects had no effect on serum TG, TC, LDL-C or HDL-C. Flaxseed with very low a-linolenic acid reduced serum TC, LDL-C and the risk ratio, elevated serum TG and very low-density lipoprotein cholesterol (VLDL-C) and had no effect on serum HDL. SDG isolated from defatted flaxseed reduced serum TC, LDL-C and the TC/HDL-C risk ratio. Serum levels of HDL-C, TG and VLDL-C remained unchanged. These results suggest that the hypocholesterolemic effect of flaxseed probably resides in the non-oily part and not in the a-linolenic acid. Reductions in hypercholesterolemic atherosclerosis by flaxseed, flaxseed with very low a-linolenic acid and SDG were 46%, 69% and 73%, respectively. The anti-atherogenic effect of SDG could be due to its antioxidant activity and also its lipid-lowering effect. (Authors abstract)
This is a follow-up study to earlier work done by the investigator to assess the role of omega 3 fatty acid, alpha-linolenic acid (ALA) and the plant lignan secoisolariciresinol diglucoside (SDG) from flax on various indices of cardiovascular disease.  ALA suppresses production of interleukin-1 (IL-1) and tumor necrosis factor (TNF), reduces monocyte production of inflammatory mediators and leukotrienes, suppresses respiratory bursts of polymorphonuclear leukocytes (PMNLs) and reduces the production of superoxide anion in monocytes. Lignans are PAF (platelet-activating factor) receptor antagonists. Flaxseed reduces the development of hypercholesterolemic atherosclerosis. The results suggest that this effect does not appear to be due to ALA, but may be due to its lignan (SDG) component. The mechanism of reduction of hypercholesterolemic atherosclerosis by SDG could be its antioxidant and lipid-lowering activities. (Editors comments)