British Journal of Nutrition

Research Article

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. Burdgea1 c1, Yvonne E. Finnegana2, Anne M. Minihanea2, Christine M. Williamsa2 and Stephen A. Woottona1

a1 Institute of Human Nutrition, University of Southampton, UK

a2 Hugh Sinclair Human Nutrition Unit, University of Reading, UK

Abstract

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.

(Received August 06 2002)

(Revised February 18 2003)

(Accepted March 31 2003)

Correspondence:

c1 *Corresponding author: Dr Graham C. Burdge, fax +44 23 804945, email g.c.burdge@soton.ac.uk

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