Seafood is an important part of a cancer patient’s diet, but so is knowing where it came from

Seafood can be part of a healthy diet for cancer patients.
Fish is an excellent source of low-fat protein, but patients struggling with digestive issues brought on by cancer treatment may find the texture and aroma unappetizing.

Seafood isn’t for everyone. Some may be put off by its soft texture, briny flavor or an aroma that may smell, well, fishy.

For others, seafood is an important part of a healthy diet. Most fish is high in protein, low in fat and rich in omega-3 fatty acids, believed to be important for heart and brain health. Fish is also a versatile food to prepare: It can be poached, grilled, broiled, fried, served with any number of sauces and sides and even eaten raw (unless you’re a cancer patient—more on that later).

On the love-hate scale for fish, cancer patients may find themselves somewhere in the middle. Fish is generally an excellent source of low-fat protein. But patients struggling with loss of appetite, nausea and digestive issues brought on by cancer treatment may find the texture and aroma unappetizing. 

Still, it’s a good idea for patients try to incorporate some fish into their diets, if they can, says Carolyn Lammersfeld, Vice President of Integrative Care at Cancer Treatment Centers of America® (CTCA). And you don’t have to eat a lot of it to garner its benefits.

“A 3- to 4-oz. portion a couple times a week is good,” Lammersfeld says. “That's probably all you need to get the health benefits.”

In this article, we’ll explore:

If you’re interested in learning more about the nutritional support or other integrative care services we offer cancer patients at CTCA®, or if you want to speak with someone about your cancer treatment options, call us or chat online with a member of our team.

Seafood’s nutritional value

Seafood is an umbrella term for dozens of species that come in a variety of shapes and sizes, from crustaceans like clams, crabs and crawfish to types as fish as small as smelts and as large as swordfish.

Considering their differences, most fish and shellfish have similar nutritional profiles. For instance, a 3-oz. serving of cod, a very healthy fish, has only 90 calories, 1 gram of fat and 20 grams of protein, while a dozen small clams have 110 calories and 1.5 grams of fat and 17 grams of protein.

Most seafood, in fact, is high in protein, with most common varieties ranging from 16 to 27 grams per serving. Seafood also is high in potassium, selenium, iron and B vitamins, and it’s rich in omega-3 fatty acids, a substance the body can’t produce on its own so it must get it from food. These essential fats are believed to support blood health, hormone production and cell signaling. Salmon, tuna, anchovies and mussels are among the best sources of omega-3 fatty acids.

For cancer patients struggling with digestive issues and weight loss, seafood may help them maintain a healthy weight while providing key nutrients.

“The omega-3 fatty acids are most concentrated in fish and may help prevent cachexia, or muscle wasting, for patients who are struggling with appetite and weight loss,” Lammersfeld says. “I encourage patients to eat a moderate amount of fish. Or, if they can’t, to take a good supplement.”

High-quality fish oil supplements are good substitutes for those who don’t like or can’t tolerate seafood, Lammersfeld says. To reduce potential aftertaste of fish oil products, she recommends storing them in the freezer and taking them out just before meals.

Some seafood is high in sodium and cholesterol. For instance, a serving of blue crab has 95 milligrams of cholesterol, nearly one-third of the daily recommended amount, and 330 milligrams of sodium, 14 percent of the daily recommended amount. Three ounces of shrimp has more than half the suggested intake of cholesterol.

Nutritional profile of some common seafood

Fish Calories Total fat (grams) Cholesterol (milligrams) Protein (grams)
Flounder 100 1.5 55 19
Haddock 100 1 70 21
Lobster 80 0.5 60 17
Oysters 100 4 80 10
Trout 140 6 55 20
Salmon 200 10 70 24
Shrimp 100 1.5 170 21

Does fish cause cancer?

That question made headlines recently when a Brown University study suggested that fish intake was “positively associated with risk of both malignant melanoma and melanoma in situ.” But the researchers said more study was needed and stopped short of suggesting people reduce their fish consumption or stop eating it.

But, researchers said, if there’s an association between seafood consumption and melanoma, it’s because of the toxins in the fish, not the fish themselves.

“We speculate that our findings could possibly be attributed to contaminants in fish, such as polychlorinated biphenyls (PCBs), dioxins, arsenic and mercury,” study author Eunyoung Cho, ScD, an associate professor of dermatology and epidemiology at Brown University, said in a news release.

Where does your fish come from?

It does no good to increase the amount of fish in your healthy diet if that fish is not healthy to eat.

Fish are only as healthy as the waters in which they swim. And when those waters are polluted, the fish may absorb some of those toxins and pass them on to those who eat them. In fact, that’s in part how fish build up toxins to begin with. Small fish with toxins are eaten by bigger fish, which are eaten by bigger fish, and so on. With each link in the food chain, the larger fish build up more toxins.

In recent years, studies on the amount of dangerous substances in fish have produced disturbing findings. For instance:

A 2016 study by Scripps Institution of Oceanography at UC San Diego  found that fish around the world were contaminated with industrial and agricultural pollutants.

A 2019 report published in Nature said “fish are the predominant source of human exposure to methylmercury, a potent neurotoxic substance.”

In 2021, Canadian researchers published a report about the alarming amount of microplastics found in fish from the Great Lakes.

“It’s important to know where your fish came from,” says Pankaj Vashi, MD, AGAF, FASPEN, Gastroenterologist and Vice Chief of Staff at CTCA Chicago. “If you’re eating fish out of Lake Michigan, you won’t want to eat it more than once a week, at most. But if you’re getting your fish from a good source, from the open ocean waters, you can certainly eat it more frequently.”

Some larger fish, especially shark and swordfish, tend to be high in mercury and other contaminants. Eating large amounts of fish that may have high levels of mercury, PCBs and other pollutants may increase the risk of illness or disease. The U.S. Environmental Protection Agency (EPA) says children and women who are pregnant or breastfeeding should limit or avoid eating fish or shellfish from certain waters.

Lammersfeld recommends using any one of a variety of phone apps that help determine whether fish options in stores or restaurants came from responsible and sustainable sources that are likely to produce healthy products.

If you’re given fish that someone else caught, the EPA recommends asking where it came from and whether consumption advisories were issued for those waters.

Mg of omega-3s   
Types of fish
More than 1,000 Anchovies, herring, mackerel, oysters, sablefish, salmon, sardines, bluefin tuna, whitefish
500 to 1,000 Mussels, coho, pink or sockeye salmon, sea bass, swordfish, tilefish, trout. albacore tuna
250 to 500 Alaska pollock, crab, flounder, sole, king mackerel, rockfish, snapper, walleye, canned tuna
Less than 250 Catfish, clams, cod, crayfish, grouper, haddock, halibut, lobster, mahi mahi, scallops, shrimp, tilapia, yellowfin tuna

Eat this fish, not that one

Most fish make good choices as part of a healthy diet—but some more than others.

The EPA categorizes fish as “best choices,” “good choices” and “choices to avoid.” Among them:  

Best choices: Salmon, cod, flounder, perch, clams, oysters, scallops, lobster, crab, sole, squid, tilapia

Good choices: Bluefish, grouper, halibut, mahi-mahi, Spanish mackerel

Choices to avoid: King mackerel, orange roughy, swordfish

Tuna, a very popular fish, is on all three lists, depending on the type. Canned light tuna is on the best list, albacore and yellowfin are on the good list, and big-eye tuna is on the list to avoid.

Cancer patients, especially those who have had a stem cell transplant, are undergoing chemotherapy or otherwise have a compromised immune system, shouldn’t eat raw fish, including clams, oysters or sushi, Lammersfeld says.

“They’re at a much higher risk of developing a foodborne illness,” she says. “A little bacterium that might make most people a little sick has the potential to make a cancer patient really sick.”

If you’re interested in learning more about the nutritional support or other integrative care services we offer cancer patients at CTCA, or if you want to speak with someone about your cancer treatment options, call us or chat online with a member of our team.