Omega-3 - what's the hype?

The potential health benefits of fish oils first received attention in the 1970s when scientists became curious about the low incidence of heart disease among the Inuit Eskimos of Greenland.

Their diets contained a lot of fat, but scientists realised marine (fish) fat was "good" fat because it had high levels of the long-chain omega-3 fats eicosapentanoic acid (EPA) and docosahexanoic acid (DHA), which are essential in our diets (see Fat facts below).

Long-chain omega-3s are incorporated into the membranes of every cell in the body, so they have a wide range of functions.

Heart disease

A World Health Organisation report concluded that the relationship between the omega-3s (EPA and DHA) and heart disease was convincing.

The Nurses' Health Study followed about 80,000 healthy women for up to 14 years. It found that the women with the highest intakes of EPA and DHA intake had a significantly lower risk of both heart disease and strokes.

Controlled clinical trials have confirmed that a steady diet of fish or fish oil supplements works as "secondary prevention", reducing the likelihood of a repeat heart attack in people who have already had a first attack.

A Food Standards Australia New Zealand review has concluded that the evidence for a benefit of EPA and DHA on heart disease is probable. Therefore there's sufficient evidence to support a general level health claim on food products.

Arthritis and joint mobility

Omega-3s are a potent anti-inflammatory. They may support joint comfort, mobility and flexibility - and so can be beneficial for arthritis sufferers.

Depression

The brain is about 60 percent fat, and the fat we eat influences its composition. Omega-3s make the membrane more flexible and the cells more receptive to incoming signals.

In 1998, psychiatrist and biochemist Joseph Hibbeln noticed that depression was up to 60 times less common in countries such as Taiwan and Japan (where people eat a lot of oily fish) compared with countries like the US and Germany (where they don't).

But evidence is mixed. In 2002, a Crop and Food Research study in New Zealand found there was a direct link between fish consumption and mental health status. However, two further studies by the same researcher found no relationship.

Vision

Omega-3s are important in the development of brain and visual function in infants, and are also associated with retaining those functions throughout life.

In one study, men with the highest fish consumption (at least two serves per week) were 45 percent less likely to have age-related macular degeneration, which is the biggest cause of blindness and severe visual impairment in older people.

Fat facts

All fats and oils are a mix of fatty acids - saturated, trans, monounsaturated and polyunsaturated. But one type usually predominates in each oil or fat.

Omega fatty acids are polyunsaturates that are essential for health - the body can't make them, so you need to include them in your diet. They have many actions, which include lowering total and LDL cholesterol, and reducing your risk of heart disease.

There are two types of omega fatty acids.

• Omega-6 is found in the oils of seeds and grains, like sunflower and corn oil.
• Omega-3 is found in seafood, and in some plants such as flaxseed and walnuts.

Too much omega-6 suppresses the action of the omega-3s. So it's important to include enough of the omega-3 long-chain fatty acids eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) in the diet.

These fats are found mainly in marine (fish) oils, and they are vital nutrients required by every cell in the body.