In the body, ALA can function as a precursor for the production of the long-chain omega-3 fatty acids EPA and DHA. However, these conversions are limited; they have been estimated to occur at rates of <8% and <4% for EPA and DHA, respectively.[1] There are many factors that can impact the efficiency of this conversion, such as sex, genetic polymorphisms, disease states, and habitual fatty acid consumption.[2][1]
For example, premenopausal women can convert ALA to EPA and DHA at a significantly greater rate due to higher levels of estrogen, which can upregulate the expression of the enzymes required for the conversion.[1][3] This likely relates to the importance of DHA during fetal development and lactation. Another contributing factor may be the level of omega-6 fatty acids consumed.
Both ALA and linoleic acid (LA) — an essential omega-6 fatty acid — compete for the same enzymes that convert them into longer chain fatty acids. Restricting LA while increasing ALA intake has been shown to increase levels of EPA and sometimes DHA in clinical trials, although the effect is small.[4]
Lastly, the dose of ALA is important. For example, a clinical trial found that 30 grams daily of ground flaxseed was sufficient to raise levels of EPA in the blood, but 10 grams daily was not.[5]
Polyunsaturated fatty acid metabolism
Adapted from Lankinen et al., 2018, Nutrients.