Extremely limited synthesis of long chain polyunsaturates in adults: implications for their dietary essentiality and use as supplements.
Level 5 - mechanism / opinion, no new human data
Narrative review of human metabolic conversion studies without systematic review methodology
PubMed 17622276 · doi:10.1139/H07-034
What was done
This narrative review examined human in vivo evidence regarding the enzymatic conversion of parent polyunsaturated fatty acids (linoleic acid and alpha-linolenic acid [ALA]) into long-chain polyunsaturated fatty acids, specifically eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid.
What was found
Human in vivo studies demonstrate that approximately 5% of ALA is converted to EPA and <0.5% of ALA is converted to DHA. Consequently, high intakes of dietary ALA have a negligible effect on plasma DHA concentrations in healthy, non-vegetarian humans. Similarly, dietary linoleic acid has a negligible effect on plasma arachidonic acid levels.
Why it matters
Because endogenous synthesis of DHA from ALA is very low, dietary ALA cannot be relied upon to significantly increase plasma DHA, supporting the consideration of preformed long-chain PUFAs like DHA as dietary essentials.
Limits
The abstract describes a narrative review rather than a systematic review or meta-analysis, and does not report search methodology, the number of included studies, or total sample size. Reported conversion rates are specifically stated for healthy, non-vegetarian humans and may not apply to other populations.
Cited by
- supports In humans, the metabolic conversion rate of dietary ALA to EPA is roughly 2% to 5%, with conversion to DHA being even lower.