An EFA, or essential fatty acid, is a type of fat your body needs to function but cannot make on its own. The word “essential” means you have to get these fats from food. There are only two true essential fatty acids: linoleic acid (an omega-6) and alpha-linolenic acid, or ALA (an omega-3). From these two building blocks, your body can produce a range of other important fats, though not always efficiently.
Why Your Body Can’t Make Them
Most fats your body needs, it can assemble from other raw materials. Essential fatty acids are the exception. Human cells lack the specific enzymes required to build linoleic acid and ALA from scratch. Plant cells have these enzymes, which is why seeds, nuts, and leafy greens are primary sources. Because you can’t synthesize them, a steady dietary supply is the only option.
The Two EFA Families
The two essential fatty acids anchor two larger families of fats that play different roles in the body.
Omega-6 family: Linoleic acid is the parent fat. Your body converts it into longer-chain omega-6 fats, most notably arachidonic acid. This derivative is the main raw material for producing signaling molecules that regulate inflammation, blood clotting, and immune responses. Common food sources of linoleic acid include soybean oil, corn oil, sunflower oil, and many nuts and seeds.
Omega-3 family: ALA is the parent fat. Your body converts it into EPA and then DHA, two longer-chain omega-3 fats with major roles in heart and brain health. The catch is that this conversion is surprisingly poor. In healthy adults, only about 5 to 10% of ALA gets converted to EPA, and just 2 to 5% becomes DHA. Women of reproductive age tend to convert somewhat more, likely due to the influence of estrogen, with rates reaching roughly 21% for EPA and 9% for DHA. This low conversion rate is why many nutrition guidelines recommend eating direct sources of EPA and DHA, such as fatty fish, rather than relying solely on plant-based ALA from foods like flaxseed and walnuts.
What EFAs Do in the Body
Essential fatty acids serve as structural components of every cell membrane in your body. They keep membranes flexible and functional, which matters for everything from how cells communicate to how nutrients pass in and out.
Beyond structure, EFAs are the raw material for a class of powerful signaling molecules that regulate inflammation, pain, blood pressure, and immune activity. When your body encounters an injury or infection, these molecules help orchestrate the response, ramping inflammation up when needed and helping resolve it afterward. This is why the balance between omega-6 and omega-3 fats matters: omega-6 derivatives tend to promote inflammation, while many omega-3 derivatives help resolve it.
EFAs and Brain Health
The brain is an unusually fat-rich organ. Over half of its dry weight is lipid, and it’s especially concentrated in long-chain omega-3 fats. DHA alone accounts for more than 90% of the omega-3 fats in brain tissue and 10 to 20% of its total fat content. It’s particularly concentrated in the gray matter and in structures at synaptic terminals, where brain cells communicate with each other.
DHA influences brain function at nearly every level. It affects membrane fluidity, which determines how well receptors and ion channels work. It supports the release of neurotransmitters, promotes the growth of new neural connections, and plays a role in myelination, the insulation process that speeds up signaling between brain cells. Research shows DHA enhances the growth of neurites (the projections neurons use to connect with each other), particularly in the hippocampus, a region central to learning and memory. It does this partly by helping organize specialized membrane structures that support neural growth and signaling.
EFAs and Heart Health
Omega-3 fats, particularly EPA and DHA, benefit the cardiovascular system through several pathways. They help blood vessels relax by boosting the production of nitric oxide, a molecule that widens arteries and lowers blood pressure. They improve the elasticity of large arteries, reduce triglyceride levels, and help stabilize plaques in coronary arteries. In clinical research, a 30-month regimen of EPA and DHA was associated with triglyceride reduction and regression of lipid-rich coronary plaques. Omega-3s also have antithrombotic properties, meaning they reduce the tendency of blood to clot inappropriately.
How Much You Need
Official adequate intake levels for omega-3s, set as ALA, are 1.6 grams per day for adult men and 1.1 grams per day for adult women. During pregnancy, the recommendation rises to 1.4 grams, and during breastfeeding, 1.3 grams. Children need less, ranging from 0.5 grams in infancy to about 0.9 grams by age eight.
For omega-6, most people in Western countries get far more than enough. The bigger concern is the ratio between the two families. Research suggests an omega-6 to omega-3 ratio of about 5:1 supports optimal health, but the typical Western diet lands closer to 20:1. This imbalance leans the body’s signaling chemistry toward a more pro-inflammatory state. Increasing omega-3 intake (through fatty fish, flaxseed, chia seeds, or walnuts) while moderating heavily processed seed oils is the most practical way to shift this ratio.
Signs of EFA Deficiency
True EFA deficiency is uncommon in people eating a varied diet, but it does occur, particularly in individuals with fat malabsorption conditions, those on very low-fat diets, or infants fed formulas lacking adequate fat. The hallmark sign is a generalized, scaly dermatitis that increases water loss through the skin. In infants, this can resemble a genetic skin condition called ichthyosis. Other signs include hair loss and a drop in platelet count. In children, prolonged deficiency can impair intellectual development. Diagnosis is typically based on these visible symptoms, though specialized lab tests exist at research centers.
Best Food Sources
For omega-6 (linoleic acid), the most concentrated sources are plant oils: soybean, sunflower, corn, and safflower oil. Nuts like walnuts and pecans are also rich in it. Most people eating a modern diet get plenty without trying.
For omega-3, the picture is more nuanced. ALA comes from flaxseed, chia seeds, hemp seeds, walnuts, and canola oil. But because the body converts ALA to EPA and DHA so inefficiently, direct sources of those longer-chain fats matter. Fatty fish like salmon, mackerel, sardines, herring, and anchovies are the richest sources of preformed EPA and DHA. Algae-based supplements provide a plant-derived alternative, which is how the fish themselves accumulate these fats in the first place.