The guide

Omega-3 and omega-6

By GyroscopeUpdated November 14, 202612 sources

Eat at least 8 ounces of fish a week, the FDA’s advice for adults. From salmon, sardines or trout that comes to about 280 to 700 mg of EPA and DHA a day. Plant omega-3 from flax, chia and walnuts is a different fat, and your body turns only a little of it into EPA and DHA.

“Omega-3” on a label can mean three different fats, and that’s most of the confusion. A bag of flaxseed and a can of sardines both say omega-3. A fish oil bottle says 1,000 mg on the front. People add these together into one number, when the fish, the flax and the capsule are doing different things.

What are the three omega-3s?

• ALA (alpha-linolenic acid) comes from plants: flaxseed, chia, walnuts and canola oil. It’s essential, since your body can’t make it, and the US Adequate Intake is 1.1 g a day for women and 1.6 g for men.
• EPA and DHA are longer chains, found mostly in fish and seafood. These are the omega-3s in the heart and brain studies, and the ones a fish oil label lists.

EPA and DHA start in algae. Fish build them up by eating algae, or smaller fish that ate algae, which is why oil made from algae works for vegans.

Your body can lengthen ALA into EPA and DHA, but not much of it. In one tracer study, young women given 700 mg of labeled ALA turned about 21% of it into EPA and 9% into DHA. In men the conversion to EPA is “limited” and to DHA “very low”, in the words of a review of these studies. A tablespoon of ground flaxseed, with 1.6 g of ALA, is good for your ALA. It isn’t a serving of fish.

How much is in each fish?

The FDA’s advice is in ounces of fish, not milligrams, so here’s what 8 ounces a week of each fish gives you per day, from the USDA’s tables.

Eight ounces is two servings the size of your palm, which is how the FDA tells you to judge 4 ounces. Salmon twice a week lands near the top of the range. Light tuna twice a week barely moves it, and shrimp hardly at all. Salmon, sardines and freshwater trout are on the FDA’s Best Choices list for mercury. King mackerel, a different fish from Atlantic mackerel, is on its list to avoid.

The omega-3 counter adds up your own week, and tells you which fish closes the gap.

Do fish oil capsules do the same thing?

That’s what VITAL set out to test. Researchers gave 25,871 US adults, men 50 and older and women 55 and older, either 1 g a day of fish oil or a placebo, and followed them for a median of 5.3 years. Each capsule held 840 mg of omega-3, 460 mg of EPA and 380 mg of DHA.

Major heart events came out about even, 386 on fish oil and 419 on placebo, a difference small enough to be chance. Heart attacks on their own were lower on fish oil, 145 against 200. The trial didn’t set out to prove that, so it’s a lead to follow up, and the main result stands.

Capsules also change the heart’s rhythm. In 2021, Gencer and colleagues pooled seven big heart trials of fish oil capsules, with 81,210 people followed for about five years. Fish oil raised the risk of atrial fibrillation, an irregular heartbeat, by about 25%. In the trials that gave more than 1 g a day, the risk was about 50% higher. Each extra gram a day added about 11%.

The newest US cholesterol guideline, from March 2026, says dietary supplements aren’t recommended to lower LDL or triglycerides, and that nonprescription fish oil is “not equivalent to” the prescription omega-3 medicines doctors use for high triglycerides. If you take one of those, keep taking it and ask your doctor before changing anything. Fish oil capsules protect your heart has the full story.

Isn’t omega-6 the problem?

Omega-6 gets blamed for a lot. Its main form, linoleic acid, is in seed oils, nuts and seeds, and it’s essential too. The US Adequate Intake is 12 g a day for women 19 to 50 and 17 g for men 19 to 50.

The worry is that it causes inflammation. In 15 randomized trials in healthy people, eating more linoleic acid didn’t raise CRP or any of the other inflammation markers measured. And in 30 cohort studies in 13 countries, with 68,659 people, those with more linoleic acid in their blood had less heart disease, fewer deaths from it and fewer ischemic strokes, the kind caused by a blocked artery.

The popular fix is to get your omega-6 to omega-3 ratio down. You can do that by eating less omega-6 without eating any more fish, which leaves your EPA and DHA where they were. The number that tracks the benefit is your EPA and DHA, and fish is what raises it. The omega-6 ratio myth goes through it.

What if you’re pregnant or breastfeeding?

The FDA says to eat 8 to 12 ounces of seafood a week that’s lower in mercury, which is 2 to 3 servings from its Best Choices list. Salmon, sardines and freshwater trout are on it. Skip the highest mercury fish: king mackerel, marlin, orange roughy, shark, swordfish, bigeye tuna and tilefish from the Gulf of Mexico. The 2026 Dietary Guidelines name the same three, “salmon, sardines, trout”, as the fish to eat in pregnancy. Capsules in pregnancy are a question for your midwife or doctor.