Conversion of alpha-linolenic acid in humans is influenced by the absolute amounts of alpha-linolenic acid and linoleic acid in the diet and not by their ratio.
BACKGROUND
Human in vivo data on dietary determinants of alpha-linolenic acid (ALA; 18:3n-3) metabolism are scarce.


OBJECTIVE
We examined whether intakes of ALA or linoleic acid (LA; 18:2n-6) or their ratio influences ALA metabolism.


METHODS
During 4 wk, 29 subjects received a control diet (7% of energy from LA, 0.4% of energy from ALA, ALA-to-LA ratio = 1:19). For the next 6 wk, a control diet, a low-LA diet (3% of energy from LA, 0.4% of energy from ALA, ratio = 1:7), or a high-ALA diet (7% of energy from LA, 1.1% of energy from ALA, ratio = 1:7) was consumed. Ten days before the end of each dietary period, [U-13C]ALA was administered orally for 9 d. ALA oxidation was determined from breath. Conversion was estimated by using compartmental modeling of [13C]- and [12C]n-3 fatty acid concentrations in fasting plasma phospholipids.


RESULTS
Compared with the control group, ALA incorporation into phospholipids increased by 3.6% in the low-LA group (P = 0.012) and decreased by 8.0% in the high-ALA group (P < 0.001). In absolute amounts, it increased by 34.3 mg (P = 0.020) in the low-LA group but hardly changed in the high-ALA group. Nearly all ALA from the plasma phospholipid pool was converted into eicosapentaenoic acid. Conversion of eicosapentaenoic acid into docosapentaenoic acid and docosahexaenoic acid hardly changed in the 3 groups and was <0.1% of dietary ALA. In absolute amounts, it was unchanged in the low-LA group, but increased from 0.7 to 1.9 mg (P = 0.001) in the high-ALA group. ALA oxidation was unchanged by the dietary interventions.


CONCLUSIONS
The amounts of ALA and LA in the diet, but not their ratio, determine ALA conversion.
Goyens
Petra L L
PL
Department of Human Biology, Maastricht University, Maastricht, Netherlands. p.goyens@hb.unimaas.nl
Spilker
Mary E
ME
Zock
Peter L
PL
Katan
Martijn B
MB
Mensink
Ronald P
RP
D001944:Breath Tests; D002247:Carbon Isotopes; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005231:Fatty Acids, Unsaturated / Q000032:analysis / Q000097:blood / Q000378:metabolism*; D005260:Female; D006801:Humans; D019787:Linoleic Acid / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D010743:Phospholipids / Q000032:analysis / Q000097:blood / Q000378:metabolism*; D017962:alpha-Linolenic Acid / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*
D002247:Carbon Isotopes; D005231:Fatty Acids, Unsaturated; D010743:Phospholipids; D017962:alpha-Linolenic Acid; D019787:Linoleic Acid