Why should our diet contain more omega-3 fatty acids?
by Prof. Andy Sinclair (RMIT).

Omega 3 fatty acid first came to prominence in the 1970’s and they are very important to health of our hearts, and also for reducing the severity of inflammation in people with arthritis and for the health of pregnant women and children.

The different omega 3 fatty acids

Most people have heard about the omega 3 fatty acids from fish, usually referred to as EPA and DHA. Others have heard about another omega 3 fatty acid referred to as ALA. What do these terms refer to and what is their role in cardiovascular health?

What is an omega 3 fatty acid?

Fatty acids are important nutrients found in fats, oils and in foods like fish, eggs, liver and meat. Fatty acids are constructed mainly from carbon and hydrogen atoms and a small proportion of oxygen - these compounds do not dissolve in water (you know, salad dressings are a mixture of oil and water and vinegar - you need to shake the bottle to get the two phases to mix as small droplets of oil in water). Omega 3 fatty acids contain three or more double bonds in each fatty acid - this means there are two fewer hydrogen atoms for each double bond. Omega 3 tells us the first double bond is 3 carbons from the end of the fatty acid as shown here:

ALA (a-linolenic acid) is an omega 3 fatty acid with 18 carbons and three double bonds and this is found in flaxseed oil, canola oil, walnut oil and soy oil. We cannot make ALA in the body so ALA is referred to as an essential fatty acid.

EPA (eicosapentaenoic acid) is an omega 3 fatty acid with 20 carbons and five double bonds and this is found in fatty fish.

DHA (docosahexaenoic acid) omega 3 fatty acid with 22 carbons and six double bonds and this is found in all fish and shell fish. It is likely that each omega 3 fatty acid has different functions in the body.

When we eat ALA a small amount is converted to EPA and in certain tissues, such as the brain and the retina, some ALA is converted to DHA. If we eat fish, the EPA and DHA are taken up into body tissues very efficiently. Therefore, the best dietary sources of the omega 3 fatty acids are from fish. On average Australians eat about 0.1 to 0.2 gram per day of EPA plus DHA, although for those who do not consume fish very often the amount is likely to be lower. To give an idea of amounts, consuming a 100 gram can of tuna (in water) provides about 0.2 gram of EPA plus DHA. It has been suggested on the basis of studies conducted around the world that the intake of these fatty acids should be more than double our current intake upper limit (even as much as 600 mg per day).

Vegetable oils containing ALA and fish oils containing EPA and DHA can have beneficial effects on the cardiovascular system and perhaps these fatty acids operate via different mechanisms.

Recent studies have indicated that a higher dietary intake of ALA is protective against fatal Ischaemic Heart Disease in women (Hu et al Am J Clin Nutr 69:890-897, 1999).

Studies using mustard seed oil (contains ALA) or fish oil (EPA and DHA) demonstrate protective benefits against second heart attacks in men (Singh et al Cardiovasc Drugs & Therapy 11:485-491, 1997).

Studies using canola oil (contains ALA) show improvements in arterial compliance, an important index of blood vessel health (Nestel et al Atheroscler Thromb Vasc Biol 17:1163-1170, 1997).

The Lyon Diet Heart study supports the beneficial effects of diets rich in ALA (from canola oil) on secondary prevention of CVD (de Lorgeril et al Lancet 343:1454-1459, 1994).

Last Updated: November 27, 2001.