Key Findings:
In this study, partially defatted flaxseed (<10% fat by wt) was assessed to determine whether the nonlipid components, especially the viscous fiber seed coat, are responsible for cholesterol-lowering effects. Supplementing the diet with partially defatted flaxseed results in reductions in serum LDL-cholesterol concentrations similar to those observed with full-fat flaxseed. The flaxseed gum was believed to be the agent responsible for these effects. No evidence was found for an antioxidant role of flaxseed components.
ABSTRACT:
Background: Currently there is considerable interest in the potential health benefits of oil seeds, such as soy and flaxseed, especially in relation to cardiovascular disease and cancer. Objective: We therefore evaluated health aspects of partially defatted flaxseed in relation to serum lipids, indicators of oxidative stress, and ex vivo sex hormone activities. Design: Twenty-nine hyper lipidemic subjects (22 men and 7 postmenopausal women) completed two 3-wk treatment periods in a randomized, crossover trial. Subjects were given muffins that contributed <20 g fiber/d from either flaxseed (<50 g partially defatted flaxseed/d) or wheat bran (control) while they consumed self-selected National Cholesterol Education Program Step II diets. Both muffins had similar macronutrient profiles. Treatment phases were separated by 2 wk. Results: Partially defatted flaxseed reduced total cholesterol (4.6 ± 1.2%; P = 0.001), LDL cholesterol (7.6 ± 1.8%; P < 0.001), apolipoprotein B (5.4 ± 1.4%; P = 0.001), and apolipoprotein A-I (5.8 ± 1.9%; P = 0.005), but had no effect on serum lipoprotein ratios at week 3 compared with the control. There were no significant effects on serum HDL cholesterol, serum protein carbonyl content, or ex vivo androgen or progestin activity after either treatment. Unexpectedly, serum protein thiol groups were significantly lower (10.8 ± 3.6%; P = 0.007) at week 3 after the flaxseed treatment than after the control, suggesting increased oxidation. Conclusions: These data indicate that partially defatted flaxseed is effective in lowering LDL cholesterol. No effects on lipoprotein ratios, ex vivo serum androgen or progestin activity, or protein carbonyl content were observed. The significance of increased oxidation of protein thiol groups with flaxseed consumption requires further investigation.