Essential fatty acids are fats your body needs but cannot make on its own. There are exactly two: linoleic acid (an omega-6) and alpha-linolenic acid, or ALA (an omega-3). Because humans lack the specific enzymes required to produce these fats from scratch, you have to get them from food. Every other fat your body needs, including saturated fats and most monounsaturated fats, can be built from the carbohydrates and proteins you eat.
Why Your Body Can’t Make Them
Fat molecules are long chains of carbon atoms, and the specific shape of each fat depends on where double bonds appear along that chain. Your body can insert double bonds at many positions, but it’s missing two critical tools: the enzymes needed to place a bond at the omega-6 or omega-3 position. Plants have these enzymes, which is why plant foods are primary sources of both essential fatty acids. Without them, your cells simply cannot build linoleic acid or ALA from any other raw material, no matter how much you eat.
The Two Families and What They Do
Omega-6: Linoleic Acid
Linoleic acid is abundant in nuts, seeds, and vegetable oils like sunflower, safflower, and soybean oil. Once inside your cells, it can be slowly converted into arachidonic acid, a longer-chain omega-6 that serves as a building block for signaling molecules involved in inflammation, immune defense, and blood clotting. That conversion is limited, though, because the enzymes involved work slowly and their activity declines further with aging, poor nutrition, and smoking.
Omega-3: Alpha-Linolenic Acid
ALA is found mainly in plant oils, especially flaxseed, soybean, and canola oil. Your body uses ALA for energy and cell membrane structure, but its most important role is serving as the starting material for two longer-chain omega-3s: EPA and DHA. These longer forms are the ones most closely linked to heart and brain health. The catch is that humans convert ALA into EPA and DHA very poorly. The overall conversion rate is roughly 5% to 8% in most people, which is why eating EPA and DHA directly from food is considered the only practical way to raise your levels.
Interestingly, women convert ALA more efficiently than men. Studies using labeled fatty acids found that women converted about 21% of ALA to EPA and 9% to DHA, compared to less than 8% and less than 4% in men. This difference is likely driven by estrogen, which may partly explain why premenopausal women tend to have higher DHA levels than men of the same age.
What EPA and DHA Do in the Body
Although EPA and DHA are not technically “essential” (since your body can make tiny amounts from ALA), they are so important and so hard to produce internally that many nutrition experts treat them as functionally essential.
DHA is the dominant omega-3 in the brain, making up a large share of the fat in neuronal membranes. It influences how flexible and permeable those membranes are, which directly affects how well receptors, ion channels, and neurotransmitters work at the synapse. In the developing brain, DHA drives the growth of new neural connections and supports the formation of new neurons, particularly in the hippocampus, a region central to learning and memory. It also helps synaptic vesicles fuse with cell membranes, a step required every time a nerve signal crosses from one neuron to the next. DHA concentrations are also especially high in the retina and in sperm cells.
EPA plays a more prominent role in producing anti-inflammatory signaling molecules and in cardiovascular function. Omega-3s as a group lower blood triglycerides through several mechanisms: they reduce the liver’s production of triglyceride-rich particles, speed up clearance of dietary fat from the bloodstream, and, in the case of DHA, produce compounds in bile that reduce fat absorption in the intestine.
Signs of Deficiency
True essential fatty acid deficiency is uncommon in people eating a varied diet, but it does occur in certain medical situations, such as prolonged intravenous feeding without fat, severe fat malabsorption, or extremely restrictive diets. The hallmark symptom is dermatitis: dry, scaly, flaky skin caused by the rapid overgrowth of skin cells and increased water loss through the skin barrier. Biochemical markers of deficiency can appear within days to weeks, but visible skin changes may not show up for weeks to months.
More subtle, subclinical shortfalls in omega-3 intake are far more common, particularly in people who eat little fish or seafood. These don’t produce the dramatic skin symptoms of full deficiency but may contribute over time to higher inflammation and less favorable blood lipid profiles.
Best Food Sources
For omega-3s, the richest whole-food sources split along plant and animal lines. A cup of ground flaxseed contains over 38,000 mg of ALA, making it by far the most concentrated plant source. A cup of black walnuts provides about 3,350 mg of ALA. Neither contains any EPA or DHA.
For preformed EPA and DHA, fatty fish is the clear winner. A 3-ounce serving of raw salmon delivers roughly 733 mg of EPA and 938 mg of DHA. Other strong choices include mackerel, sardines, herring, and anchovies. If you rely entirely on plant sources of omega-3, you’re depending on that small conversion window from ALA to EPA and DHA, which is why algae-based supplements (the original source of DHA in the marine food chain) are a common option for people who don’t eat fish.
For omega-6, most people get plenty from cooking oils, nuts, and seeds without trying. Sunflower oil, corn oil, and soybean oil are all rich in linoleic acid, and these oils are widespread in processed and restaurant food.
The Omega-6 to Omega-3 Ratio
Both essential fatty acid families compete for the same enzymes, so the balance between them matters. For most of human history, the ratio of omega-6 to omega-3 in the diet hovered around 4:1 or lower. The typical Western diet today has shifted that ratio to approximately 20:1, heavily favoring omega-6. This happened largely because of the dramatic increase in vegetable oil consumption over the past century.
A high omega-6 to omega-3 ratio tilts the body’s signaling environment toward greater inflammation, which has been linked to a higher risk of autoimmune conditions, asthma, and allergic diseases. You don’t need to obsessively track the ratio, but the practical takeaway is straightforward: most people benefit from eating more omega-3-rich foods (fatty fish, flaxseed, walnuts) and moderating their intake of omega-6-heavy cooking oils.
How Much You Need
There is no established Recommended Dietary Allowance for essential fatty acids, but the National Institutes of Health has set Adequate Intake levels. For ALA, the target is 1.6 grams per day for adult men and 1.1 grams per day for adult women. For linoleic acid, the Adequate Intake is 17 grams per day for men and 12 grams for women aged 19 to 50.
No official Adequate Intake exists for EPA and DHA specifically, though major health organizations generally recommend 250 to 500 mg of combined EPA and DHA per day for general health. Two servings of fatty fish per week will comfortably meet that target for most people. If you eat no fish at all, a tablespoon of ground flaxseed or a small handful of walnuts daily will cover your ALA needs, though your EPA and DHA levels will remain lower than those of regular fish eaters unless you supplement with an algae-based source.