Flaxseed Lowers Total and LDL Cholesterol
Flax Oil Does Not Offer the Same Lipid-Lowering Benefit
Aug 12, 2009
For several years, the cholesterol-lowering virtues of grains and their oils have been touted by nutritionists and practitioners of “natural medicine.”
Unfortunately, these claims haven’t been universally supported by research; the findings from most randomized studies have been confounded by small sample sizes, inconsistencies in products tested, and other weaknesses in study design.
Finally, however, a meta-analysis of 28 studies comparing flaxseed and its derivatives (flaxseed oil and flax lignans) with placebo or other products lends strength to claims that flaxseed confers cholesterol-lowering benefits. (Pan A, et al. Meta-analysis of the effects of flaxseed interventions on blood lipids. Am J Clin Nutr 2009;90(2):288-97)
The trials, which included nearly 1400 study subjects, were conducted between 1990 and 2008. The authors of the meta-analysis also attempted to contact investigators involved in unpublished research.
Meta-analysis Lends Statistical Power to a Group of Studies
- The meta-analysis represented a reasonably good cross section of the population: Five of the studies were conducted exclusively in postmenopausal women; one included only premenopausal women; ten trials included subjects of both sexes; ten were conducted in men only; one trial did not specify the gender composition of the study sample, and one reported results separately by gender.
- The duration of the trials ranged from two to 52 weeks, with a median duration of 8.5 weeks. Ten of the 28 trials tested flaxseed in whole, ground, or defatted form in doses ranging from 2 – 5 tablespoons (20 – 50 grams). Flaxseed oil was evaluated in 13 of the trials in doses ranging from one to 38 grams (standardized for alpha-linolenic acid).
- Flaxseed lignan was tested in daily doses ranging from 200 to 600 mg.
- Wheat, wheat bran or germ, sunflower seed, or manioc flour were used as comparison controls in the initial studies.
Flaxseed Reduces Total and LDL Cholesterol Levels
Although the study’s authors suggested caution in interpreting their findings and concluded that “further studies are needed to determine the efficiency of flaxseed on lipid profiles… and prevention of cardiovascular disease,” they also concluded that flaxseed confers cholesterol-reducing benefits:
- Both total cholesterol and LDL-cholesterol levels were reduced significantly in groups using whole flaxseed or lignan, but not oil. These reductions tended to be greater in the higher-quality studies.
- Declines in lipid values were higher in individuals who had higher lipid values at the studies’ onset (baseline).
- The highest reductions in total and LDL-cholesterol were noted in women as a group, but many of these women had higher baseline cholesterol values.
- No significant changes were seen in HDL-cholesterol or triglyceride levels in all groups and subgroups tested.
- Optimal doses of flaxseed or lignan were not addressed in the meta-analysis.
Cholesterol and Flaxseed: The Bottom Line
Whole or ground flaxseed and flaxseed lignan, but not flaxseed oil, are associated with significant reductions of both total and LDL-cholesterol levels. Flaxseed does not significantly affect levels of triglycerides or HDL-cholesterol.
Flaxseed is a widely available, edible grain that is rich in alpha-linolenic acid, lignan, and fiber; 25% of flaxseed’s dietary fiber is in soluble form. Flaxseed can be added to breads, cereals, and other foodstuffs for consumption on a daily basis.
 |
