Omega-3 and omega-6 are two families of polyunsaturated fats that your body needs but cannot make on its own. They must come from food, which is why they’re called essential fatty acids. The difference between them is structural: omega-3 fats have their first double bond at the third carbon atom from the end of the molecule, while omega-6 fats have theirs at the sixth. That small chemical distinction changes how each fat behaves in your body, influencing everything from inflammation to brain development.
Why Your Body Can’t Make Them
Human cells lack the specific enzymes needed to insert a double bond at the omega-3 or omega-6 position of a fatty acid chain. Plants have these enzymes, which is why the “parent” molecules of both families, alpha-linolenic acid (ALA) for omega-3 and linoleic acid (LA) for omega-6, originate in plant foods. Once you eat these parent fats, your liver can convert them into longer, more active forms. ALA gets converted into EPA and then DHA, the omega-3s that do most of the heavy lifting in your body. LA gets converted into arachidonic acid, the most biologically active omega-6.
There’s a catch: the conversion of ALA into EPA and DHA is inefficient, with reported rates below 15%. That’s why eating direct sources of EPA and DHA (primarily fatty fish) matters so much, rather than relying solely on plant-based ALA.
The Three Main Omega-3s
ALA is the plant-based omega-3 found in flaxseeds, chia seeds, walnuts, and canola oil. It serves mainly as an energy source and as raw material for making EPA and DHA, though as noted, that conversion is limited.
EPA plays a key role in managing inflammation. It competes with arachidonic acid (an omega-6) for the enzymes that produce signaling molecules called eicosanoids. When EPA wins that competition, the resulting eicosanoids are far less inflammatory. EPA-derived inflammatory signals are 10 to 100 times less potent at attracting immune cells to a site of inflammation than their omega-6 counterparts. EPA also gives rise to specialized compounds called resolvins that actively help resolve inflammation once it’s done its job.
DHA is concentrated in the brain, retina, and nervous system. It significantly enhances visual acuity and cognitive function, and it plays a direct role in how photoreceptor cells in the eye convert light into visual signals. During pregnancy, DHA accumulates rapidly in the fetal brain during the third trimester, and that accumulation continues through the first two years of life. DHA in the retina, by contrast, is fully in place by birth.
Omega-6 and Its Role in Inflammation
Linoleic acid, the parent omega-6, is abundant in vegetable oils like soybean, corn, sunflower, and safflower oil. It’s also a structural component of cell membranes, affecting how flexible and permeable your cells are. The body converts LA into arachidonic acid, which has a complicated reputation.
Arachidonic acid is the dominant source of eicosanoids in the body, and these signaling molecules generally promote inflammation, blood vessel constriction, and blood clotting. That sounds harmful, but acute inflammation is a necessary defense mechanism. You need it to fight infections and heal wounds. The problem arises when the balance tips too far toward omega-6-driven inflammation without enough omega-3 to counterbalance it. Arachidonic acid also supports brain energy metabolism and helps release a neurotransmitter involved in memory and learning, so it isn’t purely an inflammatory villain.
How They Compete Inside Your Body
Omega-3 and omega-6 fats share the same set of enzymes for processing. The key bottleneck is an enzyme called delta-6 desaturase, which is the rate-limiting step for converting both parent fats into their longer, more active forms. When you eat a lot of linoleic acid, it monopolizes this enzyme and slows down the conversion of ALA into EPA and DHA. The reverse is also true: more ALA means less efficient processing of LA into arachidonic acid.
This enzyme competition extends downstream too. EPA directly competes with arachidonic acid for the enzymes that produce eicosanoids. The more EPA available in your cell membranes, the fewer pro-inflammatory signals get made from arachidonic acid, and the more anti-inflammatory resolvins and protectins your body produces. This is one of the core mechanisms behind the health benefits of eating omega-3-rich foods.
The Ratio Problem in Modern Diets
For most of human history, the ratio of omega-6 to omega-3 in the diet sat around 4 to 1 or lower. The typical Western diet today has shifted that ratio to roughly 20 to 1 in favor of omega-6. This happened over the past century as refined vegetable oils became staples in cooking and processed food, while fish consumption stayed flat or declined.
To put it in concrete terms: during the Paleolithic era, daily intake of EPA and DHA is estimated at 660 to 14,250 mg. Today, most people get just 100 to 200 mg per day. That’s a dramatic drop in the omega-3s that directly reduce inflammation and support brain and heart health, combined with a surge in the omega-6s that compete against them.
Where to Find Each One
The richest direct sources of EPA and DHA are fatty fish: salmon, mackerel, sardines, herring, and anchovies. Two servings of fatty fish per week is the most common dietary guideline. For plant-based omega-3 (ALA), flaxseeds, chia seeds, hemp seeds, and walnuts are the top sources. Keep in mind that ALA alone won’t reliably raise your EPA and DHA levels due to the low conversion rate, so if you don’t eat fish, algae-based supplements are the most direct plant alternative.
Omega-6 is almost impossible to avoid in a modern diet. Soybean oil alone accounts for a large share of omega-6 intake in many countries, and it’s used widely in restaurant cooking, salad dressings, and packaged snacks. Corn oil, sunflower oil, and safflower oil are other concentrated sources. Poultry, eggs, and nuts also contain meaningful amounts. Most people get far more omega-6 than they need without trying.
Heart Health Effects
Omega-3s have well-established benefits for lowering triglycerides, and purified EPA supplements now carry a formal recommendation from the European Society of Cardiology for managing high triglycerides in high-risk patients. A 2025 meta-analysis of clinical trials published in JACC: Advances found that purified EPA reduced cardiovascular death by 21% compared to standard preventive therapy. Combinations of EPA and DHA showed a smaller but still statistically significant 8% reduction. The distinction suggests that EPA may have unique cardiovascular benefits beyond what DHA adds, though both remain important for overall health.
Brain and Eye Development
DHA is the predominant polyunsaturated fat in both the brain and the retina. It’s considered a conditionally essential nutrient for neurodevelopment, meaning that while it’s technically not “essential” by strict biochemical definition, adequate intake is necessary for normal brain growth. DHA affects rod and cone development in the eye, neuronal connectivity in the brain, and the maturation of the central nervous system.
These effects are especially critical during pregnancy and early childhood. DHA accumulates most rapidly in the fetal brain during the third trimester, and the brain continues absorbing it through age two. For this reason, getting enough long-chain omega-3s during pregnancy is important for both maternal health and fetal development. After early childhood, DHA remains important for maintaining cognitive function, though the window of most rapid accumulation has closed.
Practical Takeaways for Your Diet
The goal isn’t to eliminate omega-6 fats. They’re essential, and your body uses them for legitimate purposes, from cell membrane structure to wound healing. The goal is to shift the balance back toward omega-3. The most effective ways to do that are eating fatty fish regularly, using olive oil or avocado oil instead of soybean or corn oil for cooking, and reducing your intake of heavily processed foods that rely on high-omega-6 oils.
If you rely on plant sources alone, combine ALA-rich foods like ground flaxseed and walnuts with an algae-based DHA supplement to cover the gap that poor ALA conversion leaves open. The enzyme competition between omega-3 and omega-6 means that lowering your omega-6 intake also helps your body make better use of whatever omega-3 you do eat.