TITLE

Docosa-hexaenoic acid (DHA) accumulation is regulated by the polyunsaturated fat content of the diet: Is it synthesis or is it incorporation?

AUTHOR(S)
Gibson, R. A.
PUB. DATE
June 2004
SOURCE
Asia Pacific Journal of Clinical Nutrition;2004 Supplement, Vol. 13, pS78
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Background - Tissue levels of docosahexaenoic acid (DHA, 22:6n-3) in animals and humans are minimally influenced by increasing the level of its precursor alpha linolenic acid (ALA, 18:3n-3) in the diet. We have tested the hypothesis that this could be due either to competitive inhibition of a key step in the pathway, the conversion of dietary ALA to long chain polyunsaturated fatty acids (LCPUFA) by linoleic acid (LA, 18:2n-6) since both fatty acids (ALA, LA) are substrates for the Δ,6-desaturase or is due to LA inhibiting DHA incorporation. Methods - We tested weaning rats fed a spectrum of 54 separate diets for three weeks. The diets varied in fat content (11.8, 22.2 and 39.4 percent of energy, en%), in the levels of LA (0.07 - 17.1 en%), ALA (0.02 - 12.1 en%) and in the LA:ALA ratio (0.5:1 to 10:1). Results - The concentrations of DHA in plasma phospholipids of some dietary groups reached 9% of total fatty acids but the peak of DHA accumulation was seen within a narrow range of 1-3 en% ALA and 1-2 en% LA. Beyond 3 en% of either ALA or LA, DHA levels are uniformly low. On the other hand, plasma DHA levels were inversely correlated with plasma LA (r²=0.6) indicating that high LA intakes may inhibit incorporation of DHA. This may explain the apparent curvilinear effect of dietary ALA on synthesis of DHA. Past stable isotope experiments may not taken this into account. Conclusions - The apparent conversion of ALA to DHA is dependent on both an adequate level of ALA and a low level of LA in the diet.
ACCESSION #
34013786

 

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