Plant-based omega-3s work better than expected in a year-long diet study

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Dec 17 2025

Under carefully controlled dietary conditions, plant-based ALA from flaxseed oil meaningfully raises long-chain omega-3 levels, challenging assumptions about poor conversion while underscoring why vegans may still need algae-derived EPA and DHA.

Study: Impact of α-linolenic acid supplementation on long-chain n-3 fatty acid profiles in Western, flexitarian, vegetarian, and vegan diets. Image Credit: FamStudio / Shutterstock

In a recent study published in the journal Frontiers in Nutrition, researchers investigated whether flaxseed oil, an established rich source of plant-based alpha-linolenic acid (ALA), can meaningfully increase levels of biologically active long-chain omega-3s, EPA and DHA, in the human body under controlled dietary conditions. The study sought to evaluate whether this approach could improve omega-3 status, particularly in vegetarians and vegans who routinely exhibit low EPA and DHA levels.

Contrary to the widespread assumption that the human body only poorly converts plant-derived ALA into long-chain omega-3 fatty acids, the study found that ALA supplementation significantly increased erythrocyte EPA, DPA, and DHA levels across all dietary patterns when dietary omega-6 intake was controlled. These findings suggest that baseline omega-3 status, rather than dietary pattern or gender, is the strongest determinant of the magnitude of relative response.

Omega-3 Fatty Acids and Human Health

Decades of research have established long-chain omega-3 polyunsaturated fatty acids (PUFAs), specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), as critical determinants of cardiovascular health, brain function, and inflammation regulation.

Nutritional studies have consistently shown that fatty fish are the primary dietary source of EPA and DHA, explaining why vegetarians and vegans often exhibit substantially lower circulating levels of these fatty acids compared with omnivores.

Although previous research has demonstrated that EPA and DHA can be synthesized endogenously from ALA, this conversion is generally regarded as limited and influenced by multiple metabolic and dietary factors rather than being absent.

ALA is an essential fatty acid found in plant foods such as flaxseeds, walnuts, and chia seeds. However, many plant-based diets are also high in linoleic acid (LA), an omega-6 fatty acid that competes with ALA for the same desaturase enzymes, potentially constraining the conversion of ALA into long-chain omega-3 metabolites.

NuEva Study Design and Objectives

The present NuEva study aimed to address this knowledge gap and inform dietary guidance by investigating whether a sustained intake of flaxseed oil, embedded within a nutrient-optimized diet, could improve long-chain omega-3 status in individuals who do not consume fish. The study also examined whether factors such as age, sex, body mass index (BMI), and baseline fatty acid status influence ALA-to-omega-3 conversion.

The NuEva study is a prospective, non-randomized intervention trial involving 168 participants categorized into four dietary patterns: Western diet (omnivores), flexitarians, vegetarians, and vegans. The intervention lasted 12 months and provided participants with nutrient-optimized menu plans designed to maintain a favorable omega-6-to-omega-3 ratio, thereby reducing metabolic competition for shared enzymatic pathways.

Dietary Intervention and Measurements

From the third through the twelfth month, participants received daily flaxseed oil supplementation providing approximately 3 grams of ALA. Fatty acid profiles were assessed in both blood plasma and erythrocyte, red blood cell, membranes every three months. Sociodemographic data and medical history were also analyzed to identify potential predictors of conversion efficiency, including sex, BMI, age, and baseline fatty acid status.

Effects on Omega-3 Fatty Acid Status

Analyses revealed that consistent, moderate flaxseed oil supplementation within a controlled dietary context effectively improved omega-3 status. Levels of ALA in erythrocyte membranes increased across all diet groups by 22.5% to 38.4%.

More importantly, downstream long-chain omega-3 metabolites also increased significantly. EPA concentrations rose by 27.3% to 40.7%, docosapentaenoic acid (DPA) by 27.2% to 40.7%, and DHA by 12.8% to 26.0% across the different dietary patterns.

Despite these improvements, important differences remained between diet groups. Vegans consistently exhibited the lowest absolute concentrations of EPA and DHA. Although they demonstrated the largest relative increases in EPA and DPA during the intervention, their final absolute levels remained lower than those observed in omnivores and flexitarians.

Determinants of ALA Conversion Efficiency

Analyses of predictors of conversion efficiency showed that sex, BMI, age, linoleic acid status, and arachidonic acid status were not significant determinants of ALA conversion. Instead, baseline EPA status emerged as the strongest predictor. Participants with low initial EPA levels experienced markedly greater increases compared with those with higher baseline levels.

Phenotypic markers of desaturase activity further suggest that providing ALA within a diet characterized by a favorable omega-6 to omega-3 ratio may allow endogenous fatty acid-converting enzymes to operate with fewer competitive constraints, facilitating conversion without implying full normalization of long-chain omega-3 status.

Dietary Implications and Recommendations

This study provides robust long-term evidence that plant-derived ALA can be converted into biologically relevant long-chain omega-3 fatty acids to a greater extent than often observed in uncontrolled dietary settings, when dietary conditions are optimized. However, while flaxseed oil supplementation substantially improved omega-3 status across all dietary patterns, it did not eliminate absolute differences in EPA and DHA levels between vegans and omnivores.

To compensate for the absence of marine sources, vegetarians and vegans are therefore advised to combine regular intake of ALA-rich foods such as flaxseed and walnuts with algae-derived EPA and DHA supplements to achieve adequate long-chain omega-3 intake.