Fatty acids and lignans in unground whole flaxseed and sesame seed are bioavailable but have minimal antioxidant and lipid-lowering effects in postmenopausal women
Fatty acids and lignans in unground whole flaxseed and sesame seed are bioavailable but have minimal antioxidant and lipid-lowering effects in postmenopausal women
Year: 2009
Authors: Coulman, K.D Liu, Z. Michaelides, J. Hum, W.Q. Thompson, L.U.
Publication Name: Mol. Nutr. Food Res.
Publication Details: Volume 53, Pages 1366-1375.
Abstract:
Fatty acids and lignans in ground flaxseed and sesame seed are absorbed, metabolized, and exert some health benefits in vivo. However, it is unclear if they are absorbed, metabolized, and exert health benefits when consumed as unground whole seed; therefore, it was investigated in this study. In a randomized crossover study, 16 postmenopausal women supplemented their diets with food bars containing either 25 g unground flaxseed, sesame seed, or their combination (12.5 g each) (flaxseed+sesame seed bar, FSB) for 4wk each, separated by 4wk washout periods. Total serum n-3 fatty acids increased with flaxseed (p<0.05) and FSB (p>0.064) while serum n-6 fatty acids increased with sesame seed (p<0.05). Urinary lignans increased similarly with all treatments (p<0.05). Plasma lipids and several antioxidant markers were unaffected by all treatments, except serum gamma-tocopherol (GT), which increased with both sesame seed (p<0.0001) and FSB (p<0.01). In conclusion, fatty acids and lignans from unground seed in food bars are absorbed and metabolized; however, except for serum GT, the 25 g unground seed is inadequate to induce changes in plasma lipids and several biomarkers of oxidative stress. (Author's abstract)
Flaxseed and sesame seed have gained interest for their health benefits due to their fatty acid and lignan contents. Most work that has been done on these effects have used ground seed or purified lignans or oil, and it is unclear whether unground whole seed in flaxseed and sesame seed-containing foods would have the same nutrient availability and thus physiological effects as the ground seed. The overall aim of this study was to examine, in postmenopausal women, the bioavailability of fatty acids and lignans and the antioxidant and lipid-lowering effects of food bars containing 25 g unground flaxseed, sesame seed, or their combination. This study demonstrated that: (i) fatty acids and lignans from unground seed in food bars are absorbed and metabolized by postmenopausal women, as seen by increased serum n-6 and n-3 fatty acids and urinary lignans and (ii) consumption of food bars containing 25 g whole unground flaxseed, sesame seed, and their combination by postmenopausal women do not significantly lower blood lipids or change several biomarkers of oxidative stress, despite increased serum concentrations of PUFA and increased serum GT in case of bars containing sesame seed. Consumption of FSB tended to increase serum ALA and serum EPA increased after consumption of FSB only, but not FB, although FB contained twice the ALA and produced 32% more serum ALA than FSB. These results suggest that the combination of sesame seed with flaxseed may enhance the conversion of ALA in flaxseed to its longer chain counterparts although this needs further investigation. The bars have antioxidant capacity in vitro as measured by TEAC but this did not translate into decreased oxidative stress, as assessed by the FRAP assay, serum protein thiols, and LDL-CD. Antioxidant activity in vitro does not necessarily reflect the in vivo activity. The authors concluded that the lignans and fatty acids in 25 g of unground flaxseed and/or sesame seed in food bars are metabolized and absorbed at similar levels seen with ground flaxseed or sesame seed; however, this dose is inadequate to affect blood lipids over a 4wk period. A longer treatment time and increased number of subjects may produce a greater effect. (Editor's comments)
