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What Are Omega-3 Fatty Acids? A Complete Guide to ALA, EPA, and DHA
What is the difference between ALA, EPA, and DHA?
Where do omega-3 fatty acids come from?
Can the body convert ALA into EPA and DHA?
How do omega-3 fatty acids affect cell membranes?
What is the recommended daily intake of omega-3 fatty acids?
What is the difference between plant-based and marine omega-3?
What Are Omega-3 Fatty Acids?
Omega-3 fatty acids are a family of essential polyunsaturated fats that the human body cannot synthesise on its own. They must be obtained through diet or supplementation. The three forms that matter for human health are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Each has a distinct structure, origin, and biological role — but all three share a defining characteristic: they are incorporated into cell membrane phospholipids, where they influence how every cell in the body functions.
The initial evidence for their importance came from studies of Greenlandic Inuit populations, whose fish-heavy diet correlated with remarkably low rates of cardiovascular disease, multiple sclerosis, and inflammatory conditions — despite a diet high in total fat. Decades of subsequent research have established the mechanisms behind those observations.
What is the difference between ALA, EPA, and DHA?
ALA, EPA, and DHA are all omega-3 fatty acids but they differ in carbon chain length, metabolic origin, and primary biological function.
ALA (alpha-linolenic acid, 18:3n-3) is the plant-derived omega-3. It is found in flaxseed, chia seeds, walnuts, hemp, and certain plant oils including sacha inchi. ALA is classified as a strictly essential fatty acid — the body has no pathway to produce it. It serves as a precursor for EPA and DHA synthesis, and independently contributes to the maintenance of normal blood cholesterol levels (EFSA, EU Regulation 432/2012, at a daily intake of 2 g).
EPA (eicosapentaenoic acid, 20:5n-3) is a long-chain omega-3 found primarily in fatty fish and marine algae. It is the primary precursor of specialised pro-resolving mediators (SPMs) — including resolvins and protectins — that actively resolve inflammation rather than simply suppressing it. EPA also competes with arachidonic acid (an omega-6) for incorporation into cell membranes, reducing the production of pro-inflammatory eicosanoids.
DHA (docosahexaenoic acid, 22:6n-3) is the most structurally complex of the three. It is the dominant omega-3 in the brain (comprising approximately 40% of total fatty acids in neuronal tissue) and in the retina. DHA is incorporated into the phospholipid bilayer of cell membranes, where it increases membrane fluidity, modulates lipid raft dynamics, and influences receptor sensitivity and signal transduction.
Where do omega-3 fatty acids come from?
Omega-3 fatty acids have two primary dietary origins: plant sources (ALA) and marine sources (EPA and DHA).
Plant sources of ALA include flaxseed oil (approximately 53% ALA), sacha inchi oil (approximately 48–54% ALA — one of the highest plant concentrations known), chia seeds (approximately 18% ALA by weight), hemp seeds, walnuts, and canola oil.
Marine sources of EPA and DHA include fatty fish such as salmon, mackerel, sardines, herring, and anchovies. Krill oil provides EPA and DHA in phospholipid form, which may increase bioavailability. Microalgae are the primary producers of marine omega-3s in the food chain — fish accumulate EPA and DHA by consuming algae — making algal oil the direct plant-based source of long-chain omega-3s.
A 2025 review published in Nutrition Research Reviews noted that global oily fish consumption remains low, with typical intakes of less than 200 mg EPA and DHA per day — well below recommended levels — and that identifying accessible, affordable, and sustainable non-fish sources of long-chain omega-3s is an urgent nutritional priority.
Can the body convert ALA into EPA and DHA?
Yes, but the conversion is limited and highly variable. ALA can be metabolically converted to EPA and then DHA through a series of desaturation and elongation reactions in the liver. However, the efficiency of this conversion is constrained by enzyme competition, dietary factors, sex, age, and genetics.
Published research indicates that between 8% and 20% of dietary ALA is converted to EPA in humans, and between 0.5% and 9% is converted to DHA. Women of reproductive age convert ALA to EPA at approximately 2.5 times the rate of healthy men — likely due to hormonal influence on desaturase enzyme activity.
Several factors reduce conversion efficiency: high dietary intake of linoleic acid (omega-6), which competes for the same delta-6 desaturase enzyme; trans fats; inadequate micronutrient status (zinc, iron, B vitamins); and high total ALA intake, which paradoxically increases ALA oxidation and reduces its conversion rate.
The practical implication is that ALA and EPA/DHA are not interchangeable. ALA has its own validated biological functions — including the EFSA-authorised cholesterol claim — that are independent of its conversion capacity. EPA and DHA must be obtained directly from marine or algal sources to ensure adequate long-chain omega-3 status.
What does ALA do in the body?
ALA contributes to the maintenance of normal blood cholesterol levels. This health claim is authorised by the European Food Safety Authority (EFSA, EU Regulation 432/2012) at a daily intake of 2 g of ALA.
The mechanism involves the effect of polyunsaturated fatty acids on hepatic LDL receptor function. When ALA — and other PUFAs — replace saturated fats in the diet, they improve the expression and activity of LDL receptors on liver cell surfaces. These receptors are responsible for capturing and clearing LDL cholesterol from circulation. A 2023 review in IJMS found that ALA may favourably affect LDL cholesterol and triglyceride values in both adult and paediatric populations.
Meta-analyses of observational studies have shown that increasing dietary ALA is associated with a 10% lower risk of total cardiovascular disease and a 20% reduced risk of fatal coronary heart disease. Three major randomised controlled trials — the AlphaOmega trial, the PREDIMED trial, and the Lyon Diet Heart Study — all demonstrated benefits of ALA-rich diets on cardiovascular outcomes.
Beyond cholesterol, ALA has shown anti-hypertensive effects and contributes to balancing blood pressure. According to the 2009 EFSA scientific opinion, dietary ALA may contribute to reducing the risk of cardiovascular disease through anti-hypertensive, anti-atherosclerotic, and cardioprotective mechanisms.
What does EPA do in the body?
EPA is the principal omega-3 involved in the regulation of inflammation. Once incorporated into cell membrane phospholipids, EPA competes with arachidonic acid (omega-6) for the same enzymatic pathways. This competition reduces the production of pro-inflammatory eicosanoids — including prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) — and shifts the cellular environment toward resolution rather than amplification of inflammatory signals.
EPA is also the primary precursor of a class of molecules called specialised pro-resolving mediators (SPMs), including E-series resolvins and certain protectins. These molecules actively promote the resolution of inflammatory processes — a distinct biological function from simple anti-inflammation.
A 2025 review in Current Atherosclerosis Reports synthesising evidence from 2020 to 2025 confirmed that EPA modulates lipid metabolism, inflammation, platelet and endothelial function, and the gut-heart axis. The REDUCE-IT clinical trial demonstrated that high-dose EPA (as icosapent ethyl) reduced a composite of major cardiovascular events by 25% in patients with established cardiovascular disease and elevated triglycerides.
EPA also lowers blood triglyceride concentrations — an effect that is well-established across clinical trial data.
What does DHA do in the body?
DHA is the omega-3 most concentrated in structural tissues. It accounts for approximately 40% of total fatty acids in the brain's neuronal tissue — particularly in grey matter — and is the dominant omega-3 in the retina. It accumulates rapidly in the brain during the final trimester of pregnancy and the first 18 months of life, making it essential for neurodevelopment.
At the cellular level, DHA is incorporated into the phospholipid bilayer of cell membranes, where it increases membrane fluidity and modifies the organisation of lipid rafts — specialised membrane domains that regulate receptor function and signal transduction. A 2024 study published in iScience showed that dietary DHA supplementation significantly alters brain-cell membrane molecular packing, elasticity, and lipid miscibility.
DHA also influences inflammatory signalling. A 2024 paper in PubMed showed that DHA integrates into non-raft membrane domains, displacing cholesterol into lipid rafts and preventing the translocation of TLR4 (a key inflammatory receptor) into rafts — thereby dampening inflammatory cascade activation at the membrane level.
DHA is the precursor of D-series resolvins, protectins, and maresins — pro-resolving mediators involved in tissue repair and the active resolution of inflammation.
How do omega-3 fatty acids affect cell membranes?
Omega-3 fatty acids are direct structural components of cell membrane phospholipids. When incorporated into the phospholipid bilayer, EPA and DHA increase membrane fluidity, modify lipid raft dynamics, and alter the conformation and sensitivity of membrane-bound receptors.
This structural integration is the foundation of virtually all downstream omega-3 effects. A higher omega-3 content in cell membranes means less arachidonic acid available for pro-inflammatory eicosanoid synthesis, altered NF-κB activation (a central pro-inflammatory transcription factor), modified immune cell behaviour, and changed receptor signalling for hormones, insulin, and neurotransmitters.
Research published in Frontiers in Nutrition (2026) described this as a two-stage mechanism: membrane remodelling first increases fluidity and mechanosensor sensitivity, then reprograms the lipid mediator profile from pro-inflammatory to pro-resolving. This is why omega-3 status affects such a wide range of physiological systems — the membrane is the common denominator.
What is the recommended daily intake of omega-3 fatty acids?
Recommendations vary by form and by regulatory body.
For ALA: the EFSA-authorised health claim for the maintenance of normal blood cholesterol levels requires a daily intake of 2 g of ALA. This is achievable through diet (5 ml of sacha inchi oil provides approximately 2.4 g of ALA) or supplementation.
For EPA and DHA combined: the European Food Safety Authority recommends 250 mg per day for the general population for cardiovascular health. Higher intakes (up to 5 g per day from supplements) are considered safe by EFSA. Clinical contexts — elevated triglycerides, established cardiovascular disease — typically involve much higher doses under medical supervision.
The omega-3 index — a measure of EPA and DHA as a percentage of total fatty acids in red blood cell membranes — is increasingly used as a functional biomarker of omega-3 status. An omega-3 index above 8% is associated with the lowest cardiovascular risk in population-based studies.
What is the difference between plant-based and marine omega-3?
Plant-based omega-3 (ALA) and marine omega-3 (EPA and DHA) serve distinct and complementary functions. They are not substitutes for each other.
ALA is essential — the body cannot synthesise it — and has independently validated effects on blood cholesterol at 2 g per day (EFSA, EU 432/2012). It is the omega-3 of plant oils, seeds, and nuts, and the form most accessible through a diversified plant-rich diet.
EPA and DHA are the long-chain forms with the most robust evidence for cardiovascular, neurological, and anti-inflammatory effects. They are found reliably in fatty fish, krill, and microalgae. The body can produce them from ALA, but at rates too variable and too low to replace direct dietary intake for most people.
A growing body of evidence supports the use of both: ALA for its cholesterol-maintenance claim and dietary accessibility; EPA and DHA for their membrane-level and pro-resolving roles. Sustainability concerns around fish oil have accelerated interest in algal-derived EPA and DHA as an environmentally coherent alternative to marine sources.
How do omega-3 fatty acids relate to skin health?
Omega-3 fatty acids — particularly ALA and linoleic acid (omega-6) — are direct structural precursors of the lipids that make up the skin barrier. The stratum corneum, the outermost layer of the skin, is composed of ceramides, free fatty acids, and cholesterol. Essential fatty acids including ALA are required for ceramide synthesis and cannot be produced by the body.
A review published in Skin Pharmacology and Physiology found that polyunsaturated omega-3 fatty acids play a structural role in cutaneous keratinocyte membranes and influence the lipid composition of the stratum corneum — the same barrier that degrades after menopause, with age, and through daily stressors including hot water, alkaline soaps, and sleep deprivation.
Applied topically, oils rich in ALA and linoleic acid provide the essential fatty acid substrates that the skin barrier is structurally made of — supporting ceramide replenishment from the outside in.
How does sacha inchi oil compare to other omega-3 sources?
Sacha inchi oil (extracted from the seeds of Plukenetia volubilis, a plant native to the Peruvian Amazon) contains approximately 48–54% ALA omega-3 and 35% linoleic acid omega-6 — making it one of the highest-concentration plant sources of essential fatty acids currently available.
For comparison: flaxseed oil contains approximately 53% ALA but only 14% linoleic acid. Walnuts provide ALA at approximately 9% by weight. Chia seeds contain approximately 18% ALA.
The combination of high ALA and high linoleic acid in a single oil is what distinguishes sacha inchi — both fatty acids are required by the skin barrier, and ALA independently meets the 2 g daily threshold for the EFSA-authorised cholesterol claim in a 5 ml serving.
Written by the Dafee Science Team — published 15/06/2026. Dafeepédia content is developed from European regulatory sources (EFSA, EC Regulation 432/2012) and peer-reviewed scientific literature, and reviewed for accuracy before publication.
The Dafee Metabolic Intelligence app interprets standard lipid blood panels as metabolic patterns rather than isolated thresholds — available at app.dafee.fr.