From snapper to sole, tilapia to tilefish, there’s a wide variety of fish to choose from at your local fish counter. The American Heart Association (AHA) recommends eating at least two 3-ounce servings of fish, particularly fatty fish, per week. Fatty fish that are high in omega-3 fatty acids and have been shown to reduce your risk of heart attack or stroke, include anchovies, mackerel, black cod, salmon, bluefin tuna, and striped bass.

When it comes to selecting the best fish for a heart-healthy diet, it’s also important to factor in the possibility of environmental contaminants. According to the AHA and other leading health organizations, some types of fish may contain high levels of mercury and other harmful environmental chemicals. These contaminants can negate fish’s heart-health benefits and increase the risk of cancer, says David O. Carpenter, MD, a professor in environmental health sciences at the State University of New York in Albany.

For your heart and health in general, “the advice should not be just to eat fish but to eat the right kinds of fish,” Dr. Carpenter says.

To make sure you’re buying the best kinds of fish for your health, get up to speed about methylmercury and polychlorinated biphenyls (PCBs).

Methylmercury is a heavy metal that naturally occurs in the environment. It can also get released into the air as a gas from air pollution. From the air, mercury can fall into oceans and streams, where it is converted into a harmful form of mercury known as methylmercury. When fish swim in methylmercury-contaminated waters, the metal binds to their protein (the part you eat).

“The only significant source of methylmercury in the diet is seafood,” Carpenter says.

The Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA) recently updated their advice about eating fish and shellfish for women and children because methylmercury is harmful to an unborn baby’s and a young child’s developing neurological system. A study published in Environmental Health Perspectives linked prenatal methylmercury exposure to lower IQs in school-age children. According to the EPA and FDA, children, women who are pregnant or nursing, and women of childbearing age should avoid eating these high-mercury fish:

King mackerel
Marlin
Orange roughy
Shark
Swordfish
Tilefish from the Gulf of Mexico
Bigeye tuna

A meta-analysis published in February 2021 in the journal Environmental Research showed that exposure to mercury may be a risk factor for cardiovascular disease. In this analysis of 14 studies, including more than 34,000 participants, mercury exposure was associated with an increase in the risk of heart disease and death. If you have high blood pressure or heart disease, or have had a stroke, a study published in January 2017 in the International Journal of Environmental Research and Public Health suggests that you might want to get your mercury level checked. Your doctor can perform a simple blood or urine test, according to the New York State Department of Health.

PCBs are environmental contaminants found in oceans and streams. But unlike methylmercury, which accumulates in fish protein, PCBs gather in fish fat. The main source of PCBs in the diet are fish and seafood products, according to the EPA. Yet PCBs can also be found in red meat, chicken, eggs, and dairy products. After you consume food with PCBs, they accumulate in your body. PCBs aren’t harmful to your heart. Still, over time, “they increase the risk of every kind of cancer,” Carpenter says.

How to Identify Safe Picks at the Fish Counter

As a general rule for fish selection, keep in mind that “young fish are better than old fish, and vegetarian fish are better than carnivorous fish,” Carpenter says, because both mercury and PCBs accumulate with age and are much greater if a fish consumes other fish rather than plants.

The EPA and FDA have a list of the best fish to consume and how often to limit exposure to methylmercury. Because methylmercury can harm an unborn baby’s or young child’s developing nervous system, the list is geared for women of childbearing age, pregnant and breastfeeding women, and young children. Trouble is, the government’s fish list doesn’t factor in PCBs. “There hasn’t been enough science to systematically analyze all the species of fish,” Carpenter says. Salmon, for example, is high in omega-3s and low in mercury. “But it can be sky-high in PCBs,” Carpenter says. Tuna, on the other hand, isn’t high in PCBs but is high in methylmercury.

Top Fish Picks: High in Omega-3s, Low in Mercury, and Low in PCBs

To reel in the heart-healthy benefits of seafood’s mega omegas without increasing your cancer risk, Carpenter recommends getting hooked on fatty fish that’s low in mercury and PCBs.

Fish, particularly fatty fish, is heart healthy for several reasons.

It’s a lean source of protein. Unlike some cuts of meat, it’s not high in artery-clogging saturated fat.
Fish can also be rich in docosahexaenoic acid and eicosapentaenoic acid — two types of omega-3 fatty acids, and both unsaturated fats that are amazing multitaskers. The omega-3s from fish may decrease the risk of abnormal heart rhythms (arrhythmias).
Fish may decrease triglyceride levels (a fat in the blood), reduce the rate of arterial plaque buildup, and lower blood pressure.

“For the most part, the AHA’s list ignores the dangers of the chemicals in fish,” he says. Instead, Carpenter relies on recommendations from Seafood Watch, which is published by the Monterey Bay Aquarium.

Seafood Watch rates seafood based on its environmental sustainability, which includes monitoring for contaminants such as methylmercury and PCBs. Its recommendations are updated on a regular basis, with the ratings “Best Choice,” “Good Alternative,” and “Avoid.”

All told, for heart health, Carpenter suggests knowing your fish and not beating yourself up if you don’t get in your two weekly servings. Contrary to the recommendations of the AHA and because of the risk of contaminants, Carpenter eats fish only about once a week. “Fish should be part of a balanced diet, but two fish meals a week is not really a wise recommendation,” he says.

Additional reporting by Rachel Fairbank.