Paradoxical effect of n-3-containing vegetable oils on long-chain n-3 fatty acids in rat heart.

Flaxseed, echium, and canola oils contain alpha-linolenic acid (18:3n-3, ALA) in a range of concentrations. To examine their effect on elevating cardiac levels of long-chain n-3 FA, diets based on these n-3-containing vegetable oils were fed to rats for 4 wk. Sunflower oil, which contains little ALA, was a comparator. Despite canola oil having the lowest ALA content of the three n-3-containing vegetable oils, it was the most potent for elevating DHA (22:6n-3) levels in rat hearts and plasma. However, the relative potencies of the dietary oils for elevation of EPA (20:5n-3) in heart and plasma followed the same rank order as their ALA content, i.e., flaxseed > echium > canola > sunflower oil. This paradox may be explained by lower ALA intake leading to decreased competition for Delta6 desaturase activity between ALA and the 24:5n-3 FA precursor to DHA formation.