Seafood is high in complete protein, omega-3 fatty acids, vitamin B12, vitamin D, iodine, and selenium. Different types of fish and shellfish stand out for different nutrients, so the specific benefits depend on what you’re eating. Here’s a breakdown of what makes seafood nutritionally distinctive compared to other protein sources.
Omega-3 Fatty Acids
The nutrient most unique to seafood is omega-3 fat, specifically the two forms your body uses most readily: EPA and DHA. These support heart health, brain function, and help regulate inflammation. Your body can only convert small amounts of plant-based omega-3 into these active forms, which is why fish and shellfish are considered the best dietary source.
Fatty, oily fish contain the most. Atlantic mackerel leads the pack with about 2.5 grams of combined EPA and DHA per 100-gram serving (roughly 3.5 ounces). Farmed Atlantic salmon provides around 1.8 grams per serving, and wild sockeye salmon about 1.2 grams. Canned sardines deliver roughly 1 gram per serving. Leaner white fish like cod and tilapia contain far less, typically under 0.3 grams per serving.
High-Quality Protein
Seafood is a complete protein, meaning it contains all the essential amino acids your body needs, with high absorption rates. It’s grouped nutritionally alongside chicken, beef, and eggs. Most fish and shellfish provide 18 to 25 grams of protein per 100-gram cooked portion, with very little carbohydrate. Lean options like shrimp, tuna, and tilapia are especially protein-dense relative to their calories, making them popular choices for people focused on getting more protein without extra fat.
Vitamin B12
Shellfish are among the richest food sources of vitamin B12 on the planet. This vitamin is essential for nerve function and red blood cell production. Clams are the clear standout, containing about 98.9 micrograms per 100 grams of meat. To put that in perspective, the daily recommended intake for adults is just 2.4 micrograms, so even a small serving of clams delivers many times what you need.
Cooked oysters provide roughly 15 micrograms per 3-ounce serving, and blue mussels about 18 micrograms per cup. Most fin fish contain much smaller amounts, so if B12 is what you’re after, shellfish are the way to go.
Vitamin D
Fatty fish are one of the few natural food sources of vitamin D, a nutrient many people fall short on. Wild-caught salmon is the richest source, averaging about 988 IU per 3.5-ounce serving. Farmed salmon contains roughly a quarter of that, around 240 IU per serving. Farmed trout provides about 388 IU, and ahi tuna around 404 IU.
Lean, white-fleshed fish contain much less. Cod averages about 104 IU per 3.5 ounces, and grey sole only about 56 IU. Catfish and most shellfish contain little vitamin D. So if you’re eating fish partly for this nutrient, wild salmon and trout are your best options by a wide margin.
Iodine
Seafood dominates iodine content more than any other nutrient category. The top 15 most concentrated food sources of iodine are all seafood. Compared to other proteins, the difference is stark: ground beef contains about 7.5 micrograms per 100 grams, turkey breast about 4.8, and chicken breast just 1.2. Seafood provides at least ten times more iodine than these sources. Your thyroid gland depends on iodine to produce hormones that regulate metabolism, and many people in countries without iodized salt are deficient.
Selenium
Fish and shellfish are primary dietary sources of selenium in North American diets, alongside meat. Selenium acts as an antioxidant and plays a role in thyroid function and immune health. Tuna, halibut, sardines, and shrimp are all reliable sources. A single 3-ounce serving of most fish provides a significant portion of the daily recommended intake of 55 micrograms for adults.
Calcium and Iron From Shellfish
Seafood isn’t typically a major calcium source. Dairy provides about 72 percent of dietary calcium in the U.S., while seafood contributes only about 3 percent. There’s one notable exception: canned fish eaten with bones. A single canned Atlantic sardine with bones contains about 92 milligrams of calcium. Canned pink salmon and shellfish also provide 60 to 92 milligrams per 100 grams, making them a useful option for people who don’t eat dairy.
For iron, clams stand out among seafood at about 2.8 milligrams per 100 grams. Oysters also provide meaningful amounts. However, salmon, tuna, shrimp, and most other popular seafood contain less iron and zinc than ground beef, so if those minerals are a priority, red meat is still the more concentrated source.
Choline and Magnesium
Salmon, tuna, and cod are good sources of choline, a nutrient important for brain health and liver function. They aren’t the top dietary sources overall (eggs and meat contribute more in most people’s diets), but they add meaningfully if you eat fish regularly.
Several fish species provide moderate amounts of magnesium. Yellowtail leads with about 55 milligrams per half fillet, and bluefish provides around 50 milligrams per fillet. Cod, northern pike, and seatrout each supply about 34 to 35 milligrams per 3-ounce serving. These aren’t the highest food sources of magnesium (nuts and seeds contain more), but they contribute to your overall intake.
Mercury: Which Fish to Choose
The main safety concern with seafood is mercury, which accumulates in larger, longer-lived predatory fish. The EPA and FDA recommend eating 2 to 3 servings per week from their “Best Choices” list, which includes lower-mercury options like salmon, sardines, shrimp, tilapia, pollock, catfish, cod, clams, oysters, scallops, squid, anchovies, trout, and Atlantic mackerel. If you stick to these varieties, the nutritional benefits of regular seafood consumption far outweigh the risks.
Fish caught recreationally in lakes and rivers may carry higher mercury or other contaminants. Larger freshwater species like carp, catfish, trout, and perch are more likely to have local advisories, so it’s worth checking before eating them regularly.