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How does the body convert ALA to EPA and DHA?
Conversion from ALA to EPA and DHA
What happens in step 1: desaturation?
What happens in step 2: elongation?
The body converts ALA to EPA and DHA through a series of enzymatic steps in the liver — alternating desaturation (addition of double bonds) and elongation (addition of carbon atoms). The process is regulated, limited, and influenced by diet, sex, genetics, and omega-6 intake. Conversion to EPA reaches 8–20% of dietary ALA; conversion to DHA is far lower, typically below 1–4%.
Alpha-linolenic acid (ALA) is the essential plant-based omega-3 fatty acid. Once consumed, ALA can undergo a series of enzymatic transformations that convert it into the longer-chain omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid).
This process occurs primarily in the liver and involves multiple regulated metabolic steps.
Understanding this pathway helps clarify the relationship between plant-based omega-3 intake and long-chain omega-3 status.
Complete guide to omega-3 fatty acids
What happens in step 1: desaturation?
The first and rate-limiting step in ALA conversion involves an enzyme called Δ6-desaturase.
This enzyme introduces an additional double bond into the ALA molecule.
Key points:
- This step is shared with omega-6 metabolism
- It is considered the slowest and most competitive stage
- Enzyme activity varies among individuals
Because Δ6-desaturase is also used to metabolize linoleic acid (an omega-6 fatty acid), dietary balance plays a role in pathway dynamics.
Its main role is to convert:
• ALA (alpha-linolenic acid, omega-3) → into longer-chain omega-3s like EPA and eventually DHA
• LA (linoleic acid, omega-6) → into arachidonic acid (AA)
What happens in step 2: elongation?
After desaturation, the fatty acid chain is lengthened through the addition of two carbon atoms by elongase enzymes.
ALA (18 carbons) becomes a 20-carbon intermediate.
This elongation step prepares the molecule for further desaturation into EPA.
How is EPA formed from ALA?
Following elongation and a second desaturation step (Δ5-desaturase - Delta-5-desaturase), the molecule becomes eicosapentaenoic acid (EPA).
At this stage:
- The fatty acid contains 20 carbons
- It has 5 double bonds
- It is now classified as a long-chain omega-3
EPA can then be incorporated into cell membranes or further metabolized.
How is DHA formed from EPA?
The transformation of EPA into DHA is more complex.
It requires:
- Further elongation to 22 carbons
- Additional desaturation
- A peroxisomal β-oxidation step
This multi-stage pathway explains why DHA synthesis from ALA is generally less efficient than EPA formation.
How efficient is the ALA-to-EPA/DHA conversion?
ALA-to-EPA conversion is estimated at 8–20% in healthy adults; ALA-to-DHA conversion is far lower, typically below 1–4%. Women of reproductive age convert ALA more efficiently than men — approximately 2.5 times the rate — likely due to hormonal influence on Δ6-desaturase activity. High omega-6 intake, trans fats, and low micronutrient status (zinc, iron, B vitamins) all reduce conversion efficiency.
How does omega-6 intake affect ALA conversion?
High omega-6 intake reduces ALA conversion to EPA and DHA by competing for the same Δ6-desaturase enzyme. Both ALA (omega-3) and linoleic acid (omega-6) use this enzyme as their first metabolic step — when omega-6 intake is disproportionately high, the enzyme is occupied and ALA conversion is suppressed. The modern Western diet, with an omega-6/omega-3 ratio of 15:1 to 20:1, significantly limits this pathway.
Written by the Dafee Science Team — published 02/03/2026. Dafeepédia content is developed from European regulatory sources (EFSA, EC Regulation 432/2012) and peer-reviewed scientific literature, and reviewed for accuracy before publication.
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