Long-chain n-3 PUFA: plant v. marine sources.
Long-chain n-3 PUFA: plant v. marine sources.
Year: 2006
Authors: Williams, CM, Burdge, G.
Publication Name: Proc. Nutr. Soc.
Publication Details: Volume 65, Page 42.
Abstract:
Considerable interest exists in the health benefits of fish and fish oil consumption due to strong evidence linking long-chain omega 3 PUFA intake (EPA and DHA) with reduced risk of CVD. The intake of long-chain PUFA especially DHA in pre-term infants beneficially impacts visual and neural development. Despite the importance of the long chain omega 3 fatty acids, intakes in developed countries remain low. Research has focused on ALA conversion to EPA and DHA through the n3 PUFA elongation-desaturation pathway. This paper reviews the existing data on the conversion of ALA to the longer chain PUFAs, EPA and DHA in both men and women. Two types of studies have been employed to investigate the conversion of ALA to EPA and DHA: i) those reporting the effects of chronic increases in intake of ALA on concentrations of EPA and DHA in plasma, cell, and tissue lipid pools and ii) stable-isotope-tracer studies in which subjects consume a bolus of ALA labeled with a stable isotope to follow incorporation of the label into EPA and DHA. The effects of consuming an increased amount of ALA on the fatty acid composition of plasma cell lipids have been reported in a number of studies and have shown that intakes of ALA in the range of <1 to >18g/day result in enhanced levels of EPA in plasma and cell lipids. Many of these studies also report increases in the levels of docosapentaenoic acid (DPA) which is the direct precursor to DHA. However, DHA levels in plasma or cell lipids appear not to increase significantly with higher consumption of ALA. Stable-isotope tracer studies show considerable heterogeneity in ALA metabolism among human subjects which may be attributed to different methods, modeling, and standardization. Despite the heterogeneity of the study design and mode of expression of results, the consensus of the studies is that proportion of ALA converted to EPA is generally <10% (approximately 8%). The estimated conversion of ALA to DHA is reported to be as high as 4%, and as low as 0%. Little information is available regarding the effects of gender on bioconversion of ALA to EPA and DHA. Only two studies have specifically investigated ALA conversion in women of reproductive age. When compared to a similar study conducted in men, performed by the same researchers, it was observed that conversion of ALA to EPA and DHA in women approximately 28 years of age was substantially greater (2.5 fold and >200 fold, respectively) than observed for the men. In adult men, conversion of ALA to EPA was observed to be approximately 8%, while conversion to DHA is extremely low (<0.1%). In women, the conversion of ALA to DHA was observed to be higher at 9%. The authors state this difference may in part be a result of a lower partitioning of ALA toward b-oxidation in women versus men. Another factor favoring conversion in women may be the action of oestrogen. In conclusion, conversion of ALA to EPA and DHA appears limited in humans, but there are important differences between men and women in their capacity to synthesize EPA and DHA from ALA. However, ALA conversion does represent an important source of EPA and DHA in vegetarians and in the majority of the North American population that does not consume fish or fish oils.
