CHOLESTEROL
Most protein-rich foods including red meat and poultry as well as seafood contain cholesterol. In general, Americans consume too much cholesterol and current dietary recommendations suggest that we reduce our cholesterol intake to less than 300 milligrams per day. Almost all types of fish and shellfish contain well under 100 milligrams of cholesterol per 3 ounce cooked serving, and many of the leaner types of fish have less than 60 milligrams. For many years it was thought that shellfish contained high levels of cholesterol, but this has been proven to be untrue. Earlier methods for measuring cholesterol were found to produce artificially high results because these methods also measured other sterols found in shellfish in addition to cholesterol. We now know that most shellfish also contain less than 100 milligrams of cholesterol per 3 ounce cooked serving. Shrimp contain somewhat higher amounts of cholesterol, over 150 milligrams per 3 ounce cooked serving, and squid is the only seafood that has a significantly elevated cholesterol content which averages from 300-400 milligrams per 3 ounce cooked portion. Fish roe, caviar, and the internal organs of fish (such as livers), and the tomalley of lobsters and the mustard in crabs can contain high amounts of cholesterol.
SODIUM
Finfish and shellfish both contain sodium. Current dietary recommendation suggest that we avoid too much sodium, and many individuals have been advised to reduce their sodium intake because of hypertension (high blood pressure) or other disorders. Fish in general are low in sodium and even those species with the highest sodium levels contain less than 100 milligrams per 3 ounce cooked portion, which is less than 5 percent of the current daily recommended maximum sodium intake. Most shellfish generally have more sodium, ranging from 100 to 500 milligrams per 3 ounce cooked serving. Some processed or frozen products may contain significantly higher sodium levels. Products that are brine frozen such as crab legs may contain as much as 800 to 1000 milligrams of sodium, and other products such as the surimi or imitation shellfish products, smoked fish, and some canned products that have salt added during processing may also contain large amounts of sodium. It's a good idea to carefully read ingredient or nutritional labels for processed products to determine their sodium content.
VITAMINS AND MINERALS
Seafood is generally considered to be a reasonable but not a particularly rich source of vitamins. Fish are not a particularly rich source of B vitamins, but are comparable to many other protein-rich foods. Some of the fattier fish like mackerel and herring can be a good source of Vitamin D and some fatty fish like sardines can provide a reasonable amount of Vitamin A, but most fish are not considered to be a particularly good source of fat-soluble vitamins. Some types of seafood can provide a good source for some minerals. Canned fish such as salmon and sardines that contain bones which are softened during the canning process can be a good source of calcium, but most fish flesh doesn't provide a significant amount of calcium. Seafood can also be a good source of phosphorus, and many processed and frozen products contain added phosphorus. Some types of shellfish such as clams and oysters are a good source of iron, zinc, magnesium, copper, iodine, and other trace minerals. Most fish contain moderate to small amounts of most minerals.
NUTRIENT COMPOSITION INFORMATION
Consumers frequently have questions about the amount of specific nutrients in various kinds of seafood. Because seafood is commonly sold from bulk displays in retail seafood markets and supermarkets, nutrition information that can usually be found on a package label isn't available. Many retailers provide nutrition charts that can be used to help consumers compare one type of fish or shellfish to another. Traditionally, these charts provide information on the amount of various nutrients in 3 1/2 ounces or 100 gram portions of various types of raw seafood. In 1990 Congress passed the Nutrition Labeling and Education Act which required the U.S. Food and Drug Administration to examine and make changes in the nutritional labeling of foods. The FDA decided that retailers must voluntarily provide nutrition information on bulk foods like seafood and fruits and vegetables by displaying or giving customers access to nutrient information for the 20 most frequently consumed products in each category. The FDA also determined that the nutrient information for seafood would give the amount present in a 3 ounce cooked portion. For this reason, the information provided in the table provided at this site gives the amount of various nutrients in a 3 ounce cooked portion for the 20 most frequently consumed seafood products as well as other popular types of fish and shellfish. This information is consistent with that currently being provided by retailers.