Seafood is a good source of certain nutrients that we do not get much of from other types of food. Fish and other seafood are primarily a good source of high-quality proteins, and this applies to both lean and fatty fish. Seafood also contains marine omega-3 fatty acids, which our body can only produce to a very limited extent. Fatty fish contains the highest levels of marine omega-3 fatty acids, and although mackerel contains the most, both herring and salmon are good sources. In fact, a cod dinner will give you enough marine omega-3 for the entire day, according to the European food safety authorities.
Fatty fish is also a good source of vitamin D. Herring has the highest vitamin D content, but mackerel and salmon also contribute. Lean fish, such as cod, are the best source of iodine, while most fatty fish species contain somewhat less of this trace element. It is recommended that people eat both fatty and lean fish to get enough of all the important nutrients.