The story on fish and heart health

A diet that includes fatty fish (fish with more than 5% fat) has long been touted to support heart health. Population-based studies have found that people who regularly eat fatty fish have a lower risk of heart disease compared with those who don't eat fish.

While these were observational findings, when scientists looked closer, they found that the health benefit from fatty fish appears to be high levels of omega-3 fatty acids.

"The science linking fatty fish and heart health continues to evolve, but the evidence still points to omega-3s as a way to further protect against heart attacks and strokes," says Eric Rimm, a professor of epidemiology and nutrition at Harvard's T.H. Chan School of Public Health.

The three types

Omega-3s are essential fats, meaning the body can't make them and needs to get them from food. There are three main types of omega-3s: eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alphalinolenic acid (ALA).

EPA and DHA are found in seafood, especially fatty fish like salmon, mackerel, sardines, tuna, pollock, and cod. ALA is found mainly in nuts and seeds like flaxseed, chia seeds, pumpkin seeds, and walnuts, and in plant oils such as flaxseed, soybean, and canola oils. "Your body can use ALA to make EPA and DHA, but the conversion is modest," says Rimm.

While all three omega-3s benefit the heart, EPA and DHA found in fatty fish have a more direct effect than ALA. Still, experts recommend that both fish and plant omega-3s be part of a healthy diet.

Why are omega-3s so helpful? They reduce triglycerides (a type of fat in the blood) and increase "good" HDL cholesterol. Omega-3s slow plaque buildup in arteries that can cause blood clots and trigger heart attacks and strokes. They help to ease inflammation and lower blood pressure. It's probably no surprise that fatty fish is a staple in most science-backed heart-healthy eating patterns, such as the Mediterranean and DASH diets.

Now serving fish

Eating two 3-ounce servings of fatty fish weekly is recommended by the American Heart Association. (There doesn't appear to be extra heart benefit from eating more than this amount.) Some fatty fish have higher amounts of omega-3s than others. (See "Top catches for omega-3s".)

Not a fish fan? You can take a fish oil supplement containing both EPA and DHA. One gram a day or every other day provides well above the amount you would usually get from fish, according to Rimm — but check with your doctor.

Vegetarians (who avoid all types of meat) and vegans (who avoid all animal-based foods) can get enough omega-3s by increasing their intake of plant-based ALA, says Rimm. There also are algae-based EPA and DHA supplements available, and initial research shows their levels are comparable to fish oil.

However, relying on supplements probably shouldn't be your preferred strategy. Studies that have looked at omega-3 supplements' effect on heart health have shown mixed results. An analysis published Dec. 21, 2021, in Circulation found that taking omega-3 supplements may even slightly increase the risk of atrial fibrillation (an irregular heart rhythm).

"Based on the current evidence, there is little reason to take an omega-3 supplement if you already eat fatty fish," says Rimm.

Farmed or wild?

Most fatty fish that people buy is farmed, which is less expensive and more readily available than wild-caught fish. If people are worried about contamination, especially mercury, Rimm says that the overall risk is low whether fish is farmed or wild.

"The best advice is to eat a variety of fatty fish, but avoid frequently eating swordfish, which often have the highest levels of mercury," he says. "Overall, the benefits from eating fatty fish outweigh any possible risks from contamination."

Research has found that most farmed and wild fish have similar omega-3 amounts. The exception is farmed salmon, which actually has more omega-3s than wild. Canned fish also is on a par with wild fish in terms of omega-3s. Choose canned fish packed in water rather than oil. Some omega-3 fats are lost when the oil is drained.

How fatty fish is prepared usually doesn't matter, as cooking won't substantially change its omega-3 content, says Rimm. "However, you want to avoid fried and breaded fish, as they add extra unhealthy ingredients that your heart doesn't need."

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