PUFAs or Omega 3 Fatty Acids - two polyunsaturated fatty acids, found iin oily fish,  are very special. They are

• eicosapentaenoic acid (EPA) and
• docosahexaenoic acid (DHA) - known as Omega 3.

There has been substantial research into the benefits of Omega 3 fatty acids. They have been shown to have a lowering effect on blood fat levels thus decreasing the chances of blood vessels clogging up. They also decrease the viscosity of the blood thus helping the flow around the body. This reduces the risk of heart disease.

Research is presently going on into the benefits of Omega 3 in treating Arthritis and Psoriasis. The early results in these areas are very promising. The experts recommend that including oily fish in the diet just twice a week could make a difference to those who are at risk from a whole range of illnesses.

Most oily fish are richest in fat during the late summer and early autumn while they are leanest after spawning in the early spring.

For example, the fat content of mackerel and herring can range from as little as 1% to over 30% (of body wieght) depending on the season.

The fish we actually eat is generally only caught during a limited part of its cycle and so its fat content shows very little variation.

Algae are the only form of life that are efficient at converting the n-3 parent molecule, alpha linolenic acid, into its longer chained, more unsaturated derivatives, EPA and DHA. Human and plant cells tend to have difficulty with this process.

As all wild fish feed on algae, they are a much richer source of EPA and DHA than any other source. In comparison, the fatty acid content of aquacultured fish can vary depending on the diet that they are fed.

In general the fat of fish is mainly composed of triglycerides and the fatty acids in fish oils are much less saturated than those foundin animal fat or in most vegetable oils. The best sources of n-3 PUFA are the flesh of oil rich fish or the llivers of any white fish, but in both cases the EPA and DHA make up about 25% of the fat content.

For this reason, it is essential to encourage an increase in the intake of oily fish when aiming to increase a person’s intake of long chain n-3 fatty acids. The fat content of white fish is very low, however any fat present is also rich in EPA and DHA.

Tinned tuna is a popular oily fish, being economical, convenient and, when tinned iin brine, a low fat source of protein in the diet. Surprisingly, it is not a good source of fish oil in the diet because it is pre-cooked before canning and this process results in much of the fat being lost. The residual fat in canned tuna is only around 0.6%.

Some shellfish are quite high in cholesterol and, in the past, those people on cholesterol-reducing diets were advised to avoid shellfish in their diet. Today, this advice no longer applies.

Cholesterol-reducing diets now focus on reducing saturated fats in the diet and partially replacing them with poly and mono unsaturated fats. Fish roe however is particularly high in cholesterol and its intake should be on a limited scale.

based on the documentation of "Nutritional Aspects of Fish" prepared by the Irish Sea Fisheries Board (AN BORD IASCAIGH MHARA)