Omega-3 fatty acids reduce inflammation, lower triglycerides, support brain health, and play a role in mood regulation. These essential fats are among the most studied nutrients in modern nutrition science, with strong evidence behind several of their benefits and more nuanced findings behind others. Here’s what omega-3s actually do in your body and how much you need.
Three Types of Omega-3, and They’re Not Equal
Omega-3 comes in three main forms: ALA, EPA, and DHA. ALA is found in plant foods like flaxseed, chia seeds, and walnuts. EPA and DHA come primarily from fatty fish and algae. Your body can convert ALA into EPA and DHA, but the conversion rate is remarkably poor: only about 5 to 8% of ALA converts to EPA, and as little as 0.5 to 5% makes it to DHA. That means a tablespoon of flaxseed oil and a serving of salmon are not interchangeable sources, even if both technically contain omega-3.
This distinction matters for nearly every benefit discussed below. Most of the clinical research showing clear health outcomes used EPA, DHA, or both. If you eat a plant-based diet, algal oil supplements are one of the few direct sources of DHA and EPA that don’t come from fish.
Lowering Triglycerides
The strongest evidence for omega-3 supplementation is in triglyceride reduction. At prescription-level doses of 3 to 4 grams per day, omega-3s lower triglycerides by roughly 20 to 30% in people with elevated levels. In people with very low baseline omega-3 blood levels, reductions as high as 48% have been observed. For people already taking a statin, adding omega-3s still produces a meaningful drop, averaging about 21%.
One important detail from the American Heart Association: supplements containing both EPA and DHA can raise LDL cholesterol (the “bad” kind) at high doses, while EPA-only formulations don’t appear to have this effect. This is worth knowing if your doctor is considering omega-3s as part of a lipid-lowering strategy.
Fighting Chronic Inflammation
Omega-3s are one of the few dietary components with a well-documented anti-inflammatory effect. They work through multiple pathways. They suppress a key signaling protein that triggers the production of inflammatory immune cells. They also reduce the activity of an enzyme involved in producing pain and swelling. Perhaps most importantly, EPA and DHA compete with arachidonic acid, a fat that your body uses to make inflammatory molecules. The more omega-3 in your cells, the less raw material is available for inflammation.
A large umbrella meta-analysis, which pooled results from dozens of clinical trials, found that omega-3 supplementation significantly reduced three major markers of inflammation: C-reactive protein (a general inflammation marker your doctor might check in blood work), tumor necrosis factor alpha, and interleukin 6. These reductions were statistically significant across a wide range of health conditions. For people with autoimmune conditions, joint pain, or other inflammatory issues, this is one of the more reliable dietary interventions available.
Depression and Mood
Omega-3s can cross into brain tissue easily and interact with molecules involved in mood regulation. They also appear to reduce brain inflammation, which is increasingly recognized as a contributor to depression. Clinical trials have tested a wide range of doses for major depression, from under 1 gram to 10 grams daily, but most studies showing benefit used 1 to 2 grams per day of combined EPA and DHA.
The ratio matters. Preparations with at least 60% EPA relative to DHA appear to be the most effective for mood. This is a practical detail worth checking on a supplement label if you’re considering omega-3s for this purpose. The evidence is strong enough that some psychiatrists recommend omega-3s as a complement to standard depression treatment, though they’re not a standalone replacement for therapy or medication in moderate to severe cases.
Pregnancy and Fetal Brain Development
DHA is a structural component of brain and eye tissue, and the fetal brain accumulates it rapidly during the third trimester. Supplementing during pregnancy has shown some cognitive benefits for children, with five out of eight randomized controlled trials reporting improvements of 6 to 11% on measures of cognitive development. Doses in these studies ranged from 200 to 2,200 milligrams of DHA per day.
The results, however, are inconsistent. All eight of those same studies also reported at least one measure where supplementation made no significant difference. Evidence for benefits in language development, motor skills, vision, or reduced risk of attention disorders remains insufficient. The adequate intake for pregnant women is 1.4 grams per day of total omega-3, though many prenatal supplements specifically include DHA because of the conversion problem with plant-based ALA.
Best Food Sources
Fatty fish delivers by far the most EPA and DHA per serving. A 3-ounce portion of salmon contains about 4.5 grams of combined EPA and DHA. A mackerel fillet provides around 2.5 grams. Herring offers about 1.5 grams per 3-ounce serving. Even trout, at roughly 0.5 grams, provides a meaningful amount. Light tuna, by contrast, contains just 0.17 grams per serving, so it’s not a reliable primary source.
On the plant side, chia seeds lead with about 5 grams of ALA per ounce. A cup of walnuts provides roughly 3.3 grams of ALA, and a tablespoon of flaxseed contains about 2.35 grams. Remember, though, that ALA converts to the active forms very inefficiently. For people who don’t eat fish, algal oil (derived from algae) provides about 0.5 grams of EPA and DHA per tablespoon and is the most direct plant-based alternative.
How Much You Need
The NIH sets adequate intakes for omega-3 as total ALA: 1.6 grams per day for adult men and 1.1 grams for adult women. During pregnancy, the recommendation rises to 1.4 grams; during breastfeeding, 1.3 grams. Children’s needs range from 0.5 grams for infants to 1.2 grams for boys aged 9 to 13.
These guidelines apply specifically to ALA and represent a baseline to prevent deficiency, not an optimal therapeutic dose. No official government recommendation exists for EPA or DHA intake specifically, which creates a gap between what the guidelines say and what the clinical trial evidence supports. Most research showing benefits for triglycerides, inflammation, or mood uses 1 to 4 grams of EPA and DHA combined, well above what you’d get from meeting the ALA recommendation alone.
Risks at High Doses
Omega-3s are safe for most people at typical dietary and supplement levels, but high doses carry a specific risk worth knowing about. Clinical trial data shows a dose-dependent increase in the risk of atrial fibrillation, an irregular heart rhythm. At doses around 1,000 milligrams per day of combined EPA and DHA, the risk increases by about 12%. At 1,800 to 4,000 milligrams per day, the risk rises by roughly 50%. The absolute risk remains small, around 1%, but it’s relevant for anyone with a history of heart rhythm problems or those considering high-dose supplementation for triglycerides.
Omega-3s also have mild blood-thinning properties. At standard supplement doses this is rarely an issue, but it can become relevant before surgery or for people taking anticoagulant medications.