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

Am J Clin Nutr. 2006 Jul;84(1):44-53. doi: 10.1093/ajcn/84.1.44.


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.

Design: 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.

Conclusion: The amounts of ALA and LA in the diet, but not their ratio, determine ALA conversion.

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Breath Tests
  • Carbon Isotopes
  • Dose-Response Relationship, Drug
  • Double-Blind Method
  • Fatty Acids, Unsaturated / analysis
  • Fatty Acids, Unsaturated / blood
  • Fatty Acids, Unsaturated / metabolism*
  • Female
  • Humans
  • Linoleic Acid / administration & dosage
  • Linoleic Acid / blood
  • Linoleic Acid / metabolism*
  • Male
  • Middle Aged
  • Oxidation-Reduction
  • Phospholipids / analysis
  • Phospholipids / blood
  • Phospholipids / metabolism*
  • alpha-Linolenic Acid / administration & dosage
  • alpha-Linolenic Acid / blood
  • alpha-Linolenic Acid / metabolism*


  • Carbon Isotopes
  • Fatty Acids, Unsaturated
  • Phospholipids
  • alpha-Linolenic Acid
  • Linoleic Acid