Flaxseed oil and fish-oil capsule consumption alters human red blood cell n-3 fatty acid composition: a multiple-dosing trial comparing 2 sources of n-3 fatty acid

Am J Clin Nutr. 2008 Sep;88(3):801-9. doi: 10.1093/ajcn/88.3.801.


Background: An increase in plasma n-3 fatty acid content, particularly eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), is observed after consumption of fish oil-enriched supplements. Because alpha-linolenic acid (18:3n-3; ALA) is the direct precursor of EPA and DHA, ALA-enriched supplements such as flax may have a similar effect, although this hypothesis has been challenged because of reported low conversion of ALA into DHA.

Objective: To address this question, we designed a clinical trial in which flax oil, fish-oil, and sunflower oil (placebo group) capsules were given to firefighters (n = 62), a group traditionally exposed to cardiovascular disease risk factors.

Design: Firefighters were randomly divided into 6 experimental groups receiving 1.2, 2.4, or 3.6 g flax oil/d; 0.6 or 1.2 g fish oil/d; or 1 g sunflower oil/d for 12 wk. Blood was drawn every 2 wk, and the total phospholipid fatty acid composition of red blood cells was determined.

Results: As expected, fish oil produced a rapid increase in erythrocyte DHA and total n-3 fatty acids. The consumption of either 2.4 or 3.6 g flax oil/d (in capsules) was sufficient to significantly increase erythrocyte total phospholipid ALA, EPA, and docosapentaenoic acid (22:5n-3) fatty acid content. There were no differences among groups in plasma inflammatory markers or lipid profile.

Conclusions: The consumption of ALA-enriched supplements for 12 wk was sufficient to elevate erythrocyte EPA and docosapentaenoic acid content, which shows the effectiveness of ALA conversion and accretion into erythrocytes. The amounts of ALA required to obtain these effects are amounts that are easily achieved in the general population by dietary modification.

Publication types

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

MeSH terms

  • Adult
  • Blood Pressure
  • Body Weight
  • Dietary Fats
  • Docosahexaenoic Acids / blood
  • Dose-Response Relationship, Drug
  • Erythrocytes / drug effects
  • Erythrocytes / metabolism*
  • Fatty Acids, Omega-3 / blood*
  • Fish Oils / pharmacology*
  • Humans
  • Linseed Oil / pharmacology*
  • Middle Aged
  • Plant Oils / pharmacology
  • Sunflower Oil
  • Weight Gain*


  • Dietary Fats
  • Fatty Acids, Omega-3
  • Fish Oils
  • Plant Oils
  • Sunflower Oil
  • Docosahexaenoic Acids
  • Linseed Oil