Seafood selections that help your heart — and our planet

An assortment of seafood including whole fish, salmon fillets, and clams in the shells, displayed with herbs and lemon wedges.

If you include seafood in your diet, chances are you usually stick with familiar favorites, such as salmon, tuna, and shrimp. But the next time you visit your local fishmonger or supermarket seafood counter, consider casting a wider net. Choosing seafood that's lower on the food chain (such as herring, sardines, clams, and oysters) can benefit your cardiovascular health as well as the environment.

Seafood refers to fish and shellfish, but there's a broader category called aquatic foods, which includes any food that comes from marine or freshwater environments (see "What are aquatic foods?"). "Most people aren't aware of the many different types and advantages of aquatic foods," says Christopher Golden, associate professor of nutrition and planetary health at the Harvard T.H. Chan School of Public Health.

What are aquatic foods?

Also called blue foods, aquatic foods are animals, plants, and microorganisms that live in water. They can be wild-caught or farmed and may be sourced from freshwater lakes and rivers, coastal areas like estuaries, and the ocean.

The biggest category of aquatic foods, finfish, includes small fish no more than 18 inches long, such as anchovies, herring, and sardines; midsize fish such as mahi-mahi, salmon, trout, cod, and flounder; and large fish that can measure up to 10 feet in length, such as tuna and swordfish.

Other aquatic foods include

crustaceans (such as crabs, shrimp, krill, prawns, and lobster)
cephalopods (such as octopus and squid)
mollusks (such as clams, cockles, sea snails, mussels, and scallops)
aquatic plants (such as water spinach)
algae (seaweed).

Terrestrial vs. aquatic foods

Both the Dietary Guidelines for Americans and the American Heart Association recommend that adults eat at least two servings of seafood per week. When you use seafood to replace terrestrial animal proteins such as beef, pork, and chicken (especially processed forms), you consume less saturated fat and more omega-3 fatty acids. That, in turn, may help ease inflammation within the body and promote a more favorable balance of cholesterol and other fats in the bloodstream. It also may help explain why people who eat fish a couple of times a week are less likely to have heart attacks or die from heart disease than those who avoid fish.

Farmed salmon and canned tuna are good alternatives to hamburgers and cold cuts. But including smaller fish varieties in your diet is even better, says Golden.

Why small fish?

Anchovies, herring, mackerel, and sardines are all excellent sources not only for protein, but also micronutrients like iron, zinc, and vitamin B₁₂, as well as heart-healthy omega-3 fatty acids. Because you often eat the entire fish (including the tiny bones), small fish are also rich in calcium and vitamin D, says Golden. (Mackerel is an exception: bones in cooked mackerel are too sharp or tough to eat, although bones in canned mackerel are fine to eat.) Small fish are also less likely to contain contaminants such as mercury and polychlorinated biphenyls (PCBs) compared with large species like tuna and swordfish. Those and other large fish feed on smaller fish, which concentrates the toxins.

"Sardine and anchovies are also prominently featured in the traditional Mediterranean diet, which is considered the best diet for heart health," says Golden. Canned versions of these species, which are widely available and less expensive than fresh, are a good option. However, most canned anchovies are salt-cured and therefore high in sodium, which can raise blood pressure.

Sardines packed in water or olive oil can be

served on crackers or crusty, toasted bread with a squeeze of lemon
prepared like tuna salad for a sandwich filling
added to a Greek salad

tossed with pasta, either added to tomato sauce or with lemon, capers, and red pepper flakes.

Have you sampled these seaweed selections?

You can go even further down the aquatic food chain by eating seaweed, which includes many species of marine plants and algae. If you like sushi, you've probably had nori, the flat sheets of seaweed used to make sushi rolls. You can also find seaweed snacks in Asian markets and many mainstream grocery stores. The truly adventurous may want to try kelp jerky or a kelp burger, both sold online. Kelp is one type of brown seaweed; there are also numerous green and red species.

Nutrients in seaweed vary quite a bit, depending on species. But seaweed is low in calories, is a good source of fiber, and also contains iodine, a mineral required to make thyroid hormones. Similar to terrestrial vegetables, seaweeds contain a range of other minerals and vitamins. For now, the various types of seaweed remain fringe products here in the United States, but they may become more mainstream in the future.

Bivalve benefits

Bivalves are two-shelled aquatic creatures that include clams, oysters, mussels, and scallops. They're good sources of protein but are quite low in fat, so they aren't as rich in omega-3's as small, fatty fish. However, bivalves (which are a type of mollusk) contain several micronutrients, especially zinc and vitamin B₁₂. Zinc contributes to a healthy immune system, and vitamin B₁₂ helps form red blood cells that carry oxygen and keep nerves healthy.

Try canned mussels or oysters on crackers or bread, suggests Golden. Many people enjoy bivalves on their own, either steamed, saut'ed, or grilled. You can also add them to pasta dishes, salads, or soups.

Environmental advantages

On the whole, aquatic foods generate far fewer greenhouse gas emissions than terrestrial foods. Producing terrestrial protein foods (such as pork, chicken, dairy, and especially beef) requires land, water, pesticides, and energy to produce the grain to feed land animals.

However, farm-raised fish are also fed grain, plus fish meal made from small fish. That's why wild-caught fish tends to be more environmentally friendly — but eating small fish is an even better choice, says Golden. Salmon farmers have begun using less fish meal, and some companies have created highly nutritious feeds that don't require fish meal at all, he adds.

From a planetary health perspective, bivalves are among the best sources of animal-based protein. "Bivalves can be 'nature positive' because they don't require feed and they filter and clean up water," says Golden.

Crustacean concerns?

Doctors used to advise people with elevated blood cholesterol not to eat too much shrimp, crab, and lobster, since these shellfish are all fairly high in cholesterol. Now that experts recognize that dietary cholesterol has only a modest effect on blood cholesterol, that warning is less relevant. In addition, crustaceans are low in fat and high in protein.

But when shopping for shrimp (America's favorite type of seafood), choose carefully. Consider avoiding farmed shrimp from southeast Asia, as their production has harmful consequences for the environment and health, including habitat destruction, pollution, and antibiotic misuse. For advice on choosing environmentally sustainable shrimp and other seafood, see the Monterey Bay Aquarium's seafood guide.

Adding aquatic foods to your diet

Although we tend to think of coastal cities as the best places to find seafood, it's available throughout the United States. For less-common varieties, try larger Asian markets, which often carry a wide variety of fish and bivalves, Golden suggests.

Also, be sure to follow the FDA's advice about buying and preparing seafood safely.