Conversion of alpha-linolenic acid to eicosapentaenoic acid, docosapentaenoic acid and docosahexaenoic acids in young women.
Conversion of alpha-linolenic acid to eicosapentaenoic acid, docosapentaenoic acid and docosahexaenoic acids in young women.
Year: 2002
Authors: G C Burge, S A Wootton.
Publication Name: Brit. J. Nutr.
Publication Details: Volume 88; Page 411
Abstract:
Maintenance of appropriate levels of omega-3 long chain polyunsaturated fatty acids (n-3 LCPUFA) is important for ensuring proper cell function. Of the three principal n3 fatty acids in the diet, alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acids (DHA), ALA has been found to be the principle n-3 fatty acid in the Western diet. Intakes of ALA are estimated to be 25-fold higher than EPA and 15-fold higher than DHA. Despite the high consumption of ALA, the majority of studies investigating the beneficial effects of n-3 fatty acids have been conducted using the longer chain n-3 fatty acids, EPA and DHA. This is due to a long-standing debate relating to the metabolic fate of ALA in humans, specifically its conversion to EPA and DHA. Although evidence supports that the conversion of ALA to EPA and DHA does occur, studies have found this conversion may be modest. In addition, limited data exists on the conversion of ALA in women, as the majority of these studies have been conducted in men. Thus, the objective of this study is to measure the in vivo conversion of ALA to EPA, DPA, and DHA in women of reproductive age. Participants in this study consisted of six healthy women aged 28 years (+/- 4 years). Three days preceding the start of the study, subjects consumed three standardized test meals (total energy 11.2 MJ/d) followed by a 12h overnight fast. On study day, 700mg of labeled (U13-C) ALA was ingested as an emulsion with double cream (22g), casein (12g), beet sugar (4.5g), glucose (9g), and milkshake powder. Subjects consumed two further standardized meals at 6 and 12h after ingestion of labeled ALA, and then resumed their habitual diet for the remainder of the study. Breath samples were collected at 2h intervals following labeled ALA ingestion for 12h, and then at 24h. Venous blood samples were collected by venesection at 24, 48, and 72h, and at 1, 2, and 3 wk. Results demonstrated that (U13-C) ALA levels were greatest in cholesteryl ester (CE) (224 (sem 70) µmol/L over 21 d) compared with triacylglycerol (9-fold), non-esterified fatty acids (37-fold), and phosphatidylcholine ((PC; 7-fold). EPA levels were similar in both PC (42 (sem 8) µmol/L) and CE (42 (sem 9)) µmol/L) over 21 days. In contrast, both 13C DPA and 13C DHA were detected predominately in PC (18 (sem 4) and 27 (sem 7)µmol/L over 21 d), respectively. Importantly, estimated net fractional ALA inter-conversion to EPA was 21%, DPA 6%, and DHA 9%. Approximately 22% of administered (U13-C) ALA was recovered as 13CO2 on breath over the first 24 h. In conclusion, these conversion rates are substantially higher than found in previous studies, in which 5-10% for EPA and 2-5% for DHA were reported. Although preliminary, these results shed a new light on the importance of ALA as an n3 fatty acid – particularly for women. Early n-3 research often overlooked ALA as an important n3 fatty acid as researchers believed the conversion of ALA was not only limited, but that the beneficial effect of ALA was based solely on its conversion to the longer chain, more biologically active fatty acids EPA and DHA. Recent research, however, has demonstrated that not only is the conversion more efficient that initially believed, but ALA exerts positive health benefits that are independent of EPA and DHA. As such, consuming foods rich in ALA, such as flax oil, is an excellent way to obtain the daily-recommended amount of the all important n-3 fatty acids.
