NuTrIeNtS In SeAfOoD

Nutritional Information

Nutritionists have known for years that seafood is a source of top-quality protein. Through the educational and promotional efforts of the seafood industry, government, and academe, the general public has a sharper sense of the importance of seafood in a healthy diet. Seafood can make a significant contribution to the nutrient needs of all consumers, especially growing children and the elderly.

Nutrition is the net effect of the process by which an organism ingests and uses foods for growth and maintenance of the body. Foods are composed of specific nutrients; protein, fats, carbohydrates, vitamins, and minerals. These nutrients serve as the raw material and energy needed for the body to carry out all of its functions.

Protein

Proteins are large molecules composed primarily of amino acids. Our body's digestive enzymes break down the protein we consume to release amino acids which are in turn used to make new proteins the body uses for growth and maintenance. There are nine amino acids which the body cannot manufacture; we must get them from food. They are called essential amino acids. Seafood contains all nine essential amino acids; therefore, it is an excellent choice for meeting our daily protein needs. An added advantage of seafood is that its protein is highly digestible. The protein in seafood is more readily broken down and absorbed than the protein in red meats and poultry. This advantage makes seafood an excellent food choice for people of all ages. Fish contain 17 to 25% protein with an average content of 19 g/100 g.

Fat and Calories

What is a calorie? Many people count calories or "weight-watch," but do they really understand what they are counting? The food calorie or kilogram calorie is a measure of energy, defined as the amount of heat required to raise the temperature of one kilogram (approximately 2.2 pound) of water one degree Celsius. The calories in food supply the energy the body needs to carry out all its many functions. The nutrients in food that supply energy are fat (nine calories per gram) and carbohydrates and proteins (four calories per gram each). Most varieties of finfish and shellfish are low in fat, less than 5%, and, in many cases, less than 1% fat. Therefore, most varieties of seafood provide 100 to 200 calories per 3-1/2 ounces.

The Dietary Guidelines published by the USDA and the Department of Health and Human Services advise us to eat less total fat. More specifically, "Reduce overall fat consumption from approximately 40 to 30% of energy intake." This means that of all the calories we derive from the food we eat, only 30% of them should come from fat. The Dietary Guidelines go on to suggest the type of fat. "Reduce saturated fat consumption to account for about 10% of total energy intake, and balance that with polyunsaturated and monounsaturated fats, which should account for about 10% of energy intake each."

Seafood goes a long way to helping consumers achieve these U.S. dietary goals. The total amount of fat in seafood is very low in most varieties and the fat is rich in polyunsaturated fatty acids. It is typically the way seafood is prepared that can add fat, such as sauces and deep-fat frying, not from the fish itself. Cooking techniques such as broiling, barbecuing, poaching, microwaving, or steaming on a rack will help reduce the amount of fat in the total fish recipe. On a unit calorie basis, seafood can provide a broad range of nutrients. Increasing the intake of fish is compatible with a reduction of calorie intake and saturated fatty acid intake.

Vitamins and Minerals

There are two types of vitamins, fat soluble (A, D, E, and K) and water soluble (C and the B complex). Vitamins A and D are found in fish liver oils and in small amounts in the fatty tissues of fish. Seafood is generally low in fat, and we usually don't consume fish liver oils; therefore, seafood is not considered a significant source of the fat-soluble vitamins. There is little Vitamin C found in seafood, but it is considered an excellent source of the B complex vitamins, particularly niacin, B12 and B6. Thiamine is also found in seafoods in fair amounts.

Seafood is an excellent source of minerals. Fish are one of the most important sources of calcium. The soft bones of small fish such as sardines and smelts and canned varieties such as salmon are especially valuable sources of calcium. Other minerals in seafood include zinc (oysters and crustaceans), iron (oysters, bluefish, and shrimp), copper (oysters, crabs, and lobster), potassium (mussels, scallops, and clams), and iodine, phosphorus, and selenium (all seafood in general). Fresh seafood is low in sodium. For those who have to restrict the intake of sodium, fresh seafood is an excellent choice, although you should limit your intake of processed seafoods such as smoked, cured, and most canned seafoods. Salt is added in the processing of these seafood products as it is in imitation seafood products.

Cholesterol

Cholesterol levels are not significant in most seafood products. Finfish are generally quite low in cholesterol, with shellfish having low to moderate amounts. In the past, shellfish have been excluded from low cholesterol diets because they were believed to be high in cholesterol. New sophisticated measuring techniques have indicated that cholesterol levels of many molluscan shellfish are much lower than was previously thought. In fact, molluscs, such as clams, oysters, scallops, and mussels were found to have a large percentage of noncholesterol sterols present that appear to have a positive effect. These sterols inhibit the absorption of cholesterol eaten at the same meal. Cholesterol levels in such crustaceans as crab and lobster are similar to that found in the dark meat of chicken.

While the cholesterol in shrimp varies considerably by specie, it generally is 1-1/2 to 2 times higher than in the dark meat of chicken, but far less than in eggs. Because shellfish contain very little saturated fat, they are no longer excluded from typical low cholesterol diets.

Again, seafood fits right in when trying to meet the U.S. dietary goal --reduce cholesterol consumption to about 300 mg a day. Fish averages about 50-90 mg cholesterol per 3-1/2 ounces. Shellfish tend to contain slightly higher amounts of cholesterol; thus crustaceans (crab, lobsters, shrimp) contains 60- 100 mg/3-1/2 ounces and mollusks (clams, oysters, scallops), 40-110 mg/3-1/2 ounces. Squid and octopus may contain relatively high levels, 250 and 122 mg/3-1/2 ounces, respectively.

Fish Oils

The above indicates that seafood consumption is a good idea that is compatible with optimum dietary practices/ recommendations and that substitutions of fish for other foods can help maintain a balanced nutrient intake compatible with a low-fat diet. The consumption of fish oils may provide added significant health benefits. Fish oils may provide a protective effect in minimizing the development of several chronic degenerative diseases and may have a therapeutic effect in certain cases, for example, arthritis, atherosclerosis, and vasospasm.

Fish oils are composed of fatty acids which consist of a chain of carbon atoms with a carboxyl group at one end and a methyl group (CH3) at the other. Polyunsaturated fatty acids (PUFA) contain several double bonds between carbon atoms in the chain; the more double bonds, the higher the degree of unsaturation. Fish oils are unique in that they contains a large portion of highly unsaturated fatty acids and some fatty acids with an odd number of carbons in the chain.

Many fish oils are composed primarily of the omega-3 fatty acids. They differ from most plant oils which contains mainly the omega-6 fatty acids. The most important omega-3 fatty acids found in seafood are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Fish and shellfish ingest and accumulate omega-3 fattyacids through the food chain from algae and phytoplankton, the primary producers of omega-3 fatty acids. Man can only produce saturated and omega-9 fatty acids, which means we have to get the omega-3 fatty acids we need through our daily foods.

How do omega-3 fatty acids prevent or improve human diseases? After several medical studies, it now appears that the omega-3 fatty acids help keep our bodies from over-producing eicosanoids, a group of hormone-like substances that can, in large amounts, contribute to arthritis, asthma, heart disease, stroke, and related disorders. The eicosanoids are normally derived from the omega-6 PUFA arachidonate, found predominantly in plant oil. Omega-3 fatty acids act as an antagonist to eicosanoid synthesis, thereby lowering their production. It also forms modified eicosanoids less active than the normal compounds. A diet that balances plant foods with fish foods and their omega-3 fatty acids, remains an effective and enjoyable way to combat health problems.

Most nutrition researchers now say that eating seafood once or twice a week may be beneficial in preventing coronary heart disease. The high content of PUFA in seafood lowers serum cholesterol levels. Omega-3 fatty acids change the critical balance of certain blood components called lipoproteins, thus reducing the low-density lipoproteins (LDL) and very low density lipoproteins (VLDL) that deposit cholesterol along the artery walls. The omega-3 fatty acids also lower the levels of triglycerides, another type of fat involved in heart disease. Also, the omega-3 fatty acids form a different pattern of prostaglandin, diminishing the clotting of blood cells, reducing the number and stickiness of blood platelets, and making red blood cells more flexible so that they flow more smoothly.

Other health problems that may be controlled or alleviated by the consumption of omega-3 fatty acids from fish are asthma, arthritis, diabetes, multiple sclerosis, hypertension, migraine headaches, cancer, and some kidney diseases.

How much seafood should we eat? A Dutch study published in May 1985 in The New England Journal of Medicine concluded that "the consumption of as little as one or two fish dishes a week may be of preventive value in relation to coronary heart disease." These findings were echoed by scientists who gathered at a two-day conference on seafood and health in November 1985. They agreed that eating several seafood meals a week is a good way to cut your risk of heart disease. "I have no qualms about the American public eating three or even four meals of fish a week," said Dr. William Castelli, director of the Framingham Heart Study.

"Do Your Health a Favor Eat Seafood"

Fresh seafood is an excellent source of proteins, a good source of minerals, and some vitamins, and its is low in fats, cholesterol, and sodium. In general, seafood is one of the most nutritionally balanced foods. A seafood diet helps control weight and goes a long way toward preventing heart disease. Besides, a seafood diet is a delicious way to accomplish heart-healthy eating habits.