Omega-3 Essential Fatty Acid

Fat and Fatty Acid

Fat has a bad reputation. It is a word associated with obesity, heart disease and many other disease states. However, not all fats are bad fats.

The different types of dietary fat fall into three main groups: saturated; mono-unsaturated; and polyunsaturated.

Saturated fats are the animal-derived 'hard' fats such as butter, lard and fat in meat (and used in many processed foods). Chemically-speaking, saturated fats are a chain of carbon atoms jointed by single links, which means that the maximum amount of hydrogen is present. These are the fats to reduce in the diet.

Of the unsaturated fats (so-called because extra hydrogen atoms can be inserted chemically) monounsaturated fatty acids (MUFA) are made up of a chain of carbon atoms containing one double bond. They characteristically have a lower melting point than saturated fats and so are generally liquids (oils) rather than solids (fats). Olive oil is the best-known example of an oil which contains predominantly monounsaturated fatty acids.

A polyunsaturated fatty acid (PUFA) has more than one double bond in the chain. Two to six double bonds can be found in common edible oils. Vegetable oils such as sunflower oil, and the oils from fish contain high levels of polyunsaturates.

Polyunsaturated fatty acids are further divided into two sub-groups called omega-6 and omega-3 (sometimes referred to as w-6 or w-3 or n-6 and n-3).

Both of these groups are essential for good health and normal growth. Since they cannot be manufactured by the human body, they must be supplied in the diet. For this reason, they are often referred to as 'essential fatty acids' (EFAs).

Omega-3 Essential Fatty Acid

Omega-3 (you may sometimes see it written as n-3 or w-3) is the name given to a family of polyunsaturated fatty acids. The parent omega-3 - alpha-linolenic acid (ALA) - is described as 'essential' as, like vitamins, it must be obtained from diet. It is polyunsaturated and has 18 carbon atoms and 3 double bonds (18:3).

However, from the point of view of human nutrition, the long-chain omega-3 fatty acids eicosapentaenoic acid (20:5)and docosahexaenoic acid (22:6) - EPA and DHA - are considered much more valuable as these are the forms the body requires. In theory, humans are able to synthesise EPA and DHA from dietary ALA, but in practice this process is inefficient. Scientists have therefore concluded that EPA and DHA should be obtained from diet. Oil-rich fish and supplements such as fish oil and cod liver oil, are the richest and most readily available sources. Other sources such as krill and fortified everyday foods like bread and fruit juices are in production in a minor way in various parts of the world.

What role do EFA play in the body?

Omega-3 fatty acids play an important role as structural membrane lipids, particularly in nerve tissue and the retina and are precursors to eicosanoids - highly reactive substances such as prostaglandins and leukotrienes that act locally to influence a wide range of functions in cells and tissues.

Like all fats, EFAs provide energy. Their calorific value is similar to other fats and oils but, unlike saturated fats, they have important health roles. In fact, as their name suggest, they are essential and must be consumed regularly as the body has limited storage for them.

Both of the important EFA families - omega-6 and omega-3 - are components of nerve cells and cellular membranes. They are converted by the body into eicosanoids, leukotrienes and prostaglandins - all of which are needed on a second-by-second basis by most tissue activities in the body.

EFAs are involved in normal physiology, including:

• regulating pressure in the eye, joints, and blood vessels, and mediating immune response
• regulating bodily secretions and their viscosity
• dilating or constricting blood vessels
• regulating collateral circulation
• directing endocrine hormones to their target cells
• regulating smooth muscles and autonomic reflexes
• being primary constituents of cell membranes
• regulating the rate of cell division
• maintaining the fluidity and rigidity of cellular membranes
• regulating the inflow and outflow of substances to and from cells
• transporting oxygen from red blood cells to the tissues
• maintaining proper kidney function and fluid balance
• keeping saturated fats mobile in the blood stream
• preventing blood cells from clumping together (blood clots that can be a cause of heart attack and stroke)
• mediating the release of inflammatory substances from cells that may trigger allergic conditions
• regulating nerve transmission and communication
• If the diet is deficient in either omega-6 or omega-3 long-term degenerative illnesses will result.

However, because the end product (eg prostaglandin, leukotriene) of EFA metabolism differ slightly but significantly from omega-6 to omega-3, they must be present in balance for optimum health.

Getting the ballance right

Both omega-6 and omega-3 fatty acids are essential but the body requires them in a ratio that is not normally achieved by the typical diet of today's industrialised nations.

Experts think that man evolved on a diet which would have had roughly 1-2 times more omega-6 than omega-3, though there is a school of thought which argues for a 1:1 ratio. Currently, average UK intakes are in a ratio of around 8:1 in favour of the omega-6s, while in the US it is around 10:1, and in Australia nearer 12:1. Many individuals within those populations will have an even greater omega-6 to omega-3 imbalance.

Because of their wide-ranging roles, virtually every area of the human body is susceptible to problems if the balance of the two polyunsaturates becomes out of kilter. How extreme the imbalance needs to be before problems are felt is not yet known for sure and in practice it will probably vary from one person to the next.