Volume 90, Issue 2, August (2003), pp. 311-321 © The Author 2003
doi:10.1079/BJN2003901

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Effect of altered dietary n-3 fatty acid intake upon plasma lipid fatty acid composition, conversion of [13C]α-linolenic acid to longer-chain fatty acids and partitioning towards β-oxidation in older men

Graham C. Burdge¹, Yvonne E. Finnegan², Anne M. Minihane², Christine M. Williams², Stephen A. Wootton^1
1Institute of Human Nutrition, University of Southampton, UK
²Hugh Sinclair Human Nutrition Unit, University of Reading, UK

 (Received 6 August 2002–Revised 18 February 2003–Accepted 31 March 2003)

These results have been described previously, in part, in abstracts (Burdge GC, Finnegan YE, Minihane AM, Wright P, Williams CM & Wootton SA (2001) Limited conversion of α-linolenic acid to docosahexaenoic acid in men. Proc Nutr Soc 60, 232A; Burdge GC, Finnegan YE, Minihane AM, Wright P, Williams CM & Wootton SA (2001) α-Linolenic acid metabolism in men: effect of altering dietary n-3 polyunsaturated fatty acid intake. Proc Nutr Soc 60, 233A).

The effect of increased dietary intakes of α-linolenic acid (ALNA) or eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for 2 months upon plasma lipid composition and capacity for conversion of ALNA to longer-chain metabolites was investigated in healthy men (52 (sd 12) years). After a 4-week baseline period when the subjects substituted a control spread, a test meal containing [U-¹³C]ALNA (700 mg) was consumed to measure conversion to EPA, docosapentaenoic acid (DPA) and DHA over 48 h. Subjects were then randomised to one of three groups for 8 weeks before repeating the tracer study: (1) continued on same intake (control, n 5); (2) increased ALNA intake (10 g/d, n 4); (3) increased EPA+DHA intake (1·5 g/d, n 5). At baseline, apparent fractional conversion of labelled ALNA was: EPA 2·80, DPA 1·20 and DHA 0·04 %. After 8 weeks on the control diet, plasma lipid composition and [¹³C]ALNA conversion remained unchanged compared with baseline. The high-ALNA diet resulted in raised plasma triacylglycerol-EPA and -DPA concentrations and phosphatidylcholine-EPA concentration, whilst [¹³C]ALNA conversion was similar to baseline. The high-(EPA+DHA) diet raised plasma phosphatidylcholine-EPA and -DHA concentrations, decreased [¹³C]ALNA conversion to EPA (2-fold) and DPA (4-fold), whilst [¹³C]ALNA conversion to DHA was unchanged. The dietary interventions did not alter partitioning of ALNA towards β-oxidation. The present results indicate ALNA conversion was down-regulated by increased product (EPA+DHA) availability, but was not up-regulated by increased substrate (ALNA) consumption. This suggests regulation of ALNA conversion may limit the influence of variations in dietary n-3 fatty acid intake on plasma lipid compositions.

Keywords:
α-Linolenic acid, Stable isotope, Dietary n-3 polyunsaturated fatty acids, Man

Abbreviations:
ALNA, α-linolenic acid, DHA, docosahexaenoic acid, DPA, docosapentaenoic acid, EPA, eicosapentaenoic acid, FA, fatty acid, PC, phosphatidylcholine, TAG, triacylglycerol