Purpose: The primary endpoint was to determine the plasma concentration of alpha-linolenic acid (ALA), and its metabolites, following milled flaxseed consumption at four doses. Secondary outcomes focused on plasma enterolignan concentrations and the effects on tolerability, platelet aggregation, plasma lipids and urinary thromboxane levels.
Methods: Healthy, younger adults (n = 34; 18-49 years old) were randomized into four groups consuming one muffin daily for 30 days fortified with 10, 20, 30 or 40 g of milled flaxseed. Blood and urine were collected at baseline and 4 weeks.
Results: Plasma ALA concentrations increased with all flaxseed doses (P < 0.01), except the 20 g/day dose (P = 0.10), yet there was no significant dose-dependent response (P = 0.81). Only with the 30 g/day diet were n-3 polyunsaturated fatty acids (P = 0.007), and eicosapentaenoic acid (EPA) (P = 0.047) increased from baseline values. Docosapentaenoic acid and docosahexaenoic acid were not detected at any dose. Plasma total enterolignan concentrations significantly increased over time in all treatment groups, yet despite a dose-dependent tendency, no between-group differences were detected (P = 0.22). Flaxseed was well tolerated, even at the highest dose, as there were no reported adverse events, changes in cholesterol, platelet aggregation or urinary 11-dehydro-thromboxane B2.
Conclusions: In healthy, younger adults, 10 g/day of milled flaxseed consumption is sufficient to significantly increase circulating ALA and total enterolignan concentrations; however, 30 g/day is required to convert ALA to EPA. Although all doses were well tolerated, 40 g/day is too low to attenuate cholesterol in this population.
Keywords: Alpha-linolenic acid; Cardiovascular disease; Enterolignans; Flaxseed; Platelets.