Get your omega-3 from fish

Nutritionist Rose Carr explains why we need to include omega-3 in our diets and how to do it.

Traditionally, Eskimos of Greenland consumed an enormous amount of fish in their diet and it's no coincidence that death from cardiovascular disease amongst their population was virtually unheard of. Since this link was discovered over 30 years ago, scientists have spent a lot of time investigating the omega-3 fats found in fish and what effect they have on our health.

If they are not supplied in the diet, our bodies make some fats themselves. But the 'essential fats' are the ones our bodies can't make; these include fats from the omega-6 and omega-3 groups.

Omega-3 health benefits

Long-chain omega-3s are widely accepted as having both a preventive and a treatment role in heart disease. They're good for the heart as they help to lower blood pressure and cholesterol levels and it's now thought they also help prevent arrhythmia.

Because of their protective role in inflammation and immune response, omega-3s are beneficial for sufferers of rheumatoid arthritis and there's some evidence that they're effective in treating both Crohn's disease and psoriasis. It's also possible they may help to alleviate childhood asthma but that's less conclusive.

Long-chain omega-3s are especially abundant in cells of the brain and eyes: they've been shown to be important in the development of brain and visual function in infants, and are also associated with retaining those functions throughout life. They help protect against the cognitive decline of older age and the risk of developing Alzheimer's disease. They're helpful in reducing the likelihood or severity of post-natal depression; and in people with mental health problems, including dementia, they help to improve depressive, aggressive and psychotic symptoms.

Diets high in omega-3 from fish are also strongly linked to: healthy bones (reduced risk of osteoporosis); reduced risk of developing age-related macular degeneration (the biggest cause of blindness and severe visual impairment among older people); and improved insulin sensitivity, useful in the prevention (rather than treatment) of type 2 diabetes.

Are all omega-3s equal?

No. The beneficial 'long-chain' omega-3s are EPA, DHA and DPA (so-called because of their chemistry). The other omega-3 fat is ALA.

ALA is found in plant-based foods like legumes, canola oil, flaxseed (linseed) products, walnuts and small amounts in green vegetables.

ALA can be converted into long-chain omega-3s in the body but a high ratio of omega-6 fats in the diet (which is now typical of Western diets) reduces the amount of ALA that can be converted. This is because omega-3s and omega-6s compete for the same metabolic pathways. It is for this reason that we should focus on consumption of long-chain omega-3s, especially the more common EPA and DHA, which are only found in seafood.

If you consume a typical Western diet high in omega-6 then it is unlikely you will benefit from using flaxseed oil (or other forms of ALA) as the amount of omega-6 in your diet will stop the ALA being converted to EPA and DHA.

If you are a vegetarian who has a low intake of fried foods and other omega-6 sources then your omega-6 may be relatively low and flaxseed oil is likely to be beneficial as your body will be able to convert it to EPA and DHA.

Omega-6 health benefits

Omega-6 fats help fluids move between the cells in our bodies, so in severe conditions, such as a famine, a deficiency in this type of fat can lead to dry and cracked skin. They also affect our response to inflammation. Most of our omega-6 fats come from sunflower and soy bean oils.

The omega ratio

Increasingly, it appears to be the proportions in which the omega-3 and omega-6 fats are eaten, rather than the exact amounts that are important. This is because too much omega-6 fat suppresses the action of the omega-3s. While omega-6 fats are essential to our health, the amount in Western diets, and therefore the ratio of omega-6 to omega-3, has increased over the centuries. That's because we now use more vegetable cooking oils (like soy bean, safflower and sunflower), and eat fried foods and processed foods which have tended to use omega-6 fats. It is recommended we eat omega-6 and omega-3 in a ratio of 4:1 or lower, not the 20:1 seen in many Western diets today.

How do we do this? Using a monounsaturated fat in cooking, such as olive or canola oil, reduces omega-6 fats. At the same time eat more oily fish to redress the balance.

How much do we need?

An adequate intake of long-chain omega-3s is estimated to be 90mg a day for women and 160mg for men. The Ministry of Health recently issued 'suggested dietary targets' (SDTs) for the omega-3s that will help reduce the risk of chronic disease, especially heart disease. For women the recommended intake is 430mg per day and for men it's 610mg per day.

The general advice for some time has been to have two fish meals every week, but as you can see in the table (SEE RIGHT), some fish are better sources of omega-3 than others. Don't worry about your cooking method: whether it's baked or microwaved doesn't make too much difference, just don't deep-fry your fish or you'll eat fats you don't need.

Where to get your long-chain omega-3

Fresh salmon

The richest source of long-chain omega-3s readily available to us is fresh (or fresh smoked) salmon. It is so rich in omega-3s that you need very little to meet the SDT. If you consumed 25g of smoked salmon (which is a tiny amount) you would get around 1850mg of long-chain omega-3s. That's 4 1/2 days' worth for women and 3 days' worth for men. The 25g of smoked salmon might cost around $2.

If you buy a 90g fillet of fresh salmon it might cost $2.50, but it will provide around 6660mg of long-chain omega-3s: that's 15 days' worth for women and 10 days' worth for men.

Canned salmon

This is a good source of omega-3 but the amount varies so check the nutrition information on the can. We found:

• 85g can Sealord red salmon contains 1410mg long-chain omega-3s (3 days' worth for women; 2 days worth for men)
• 95g can John West salmon tempters contains 415mg long-chain omega-3s (1 day's worth for women; less than 1 day's worth for men)

Tuna

Fresh tuna is an excellent source of long-chain omega-3s but canned tuna can be a lot lower, so check the label. The Ocean Pure range (the only one canned in New Zealand) is an exception to this as their processing technqiue is quite different from the others.

• 120g of fresh tuna contains between 900-1450mg long-chain omega-3s (2-3 days' worth for women; 1-2 days' worth for men)
• Half of a 185g can of Ocean Pure albacore tuna in olive oil contains 1083mg long-chain omega-3s (over 2 days' worth for women; less than 2 days' worth for men)
• 95g can of Sealord tuna (sweet Thai chilli) contains 94mg; an 85g pouch of Greenseas tuna (in spring water) contains 205mg (less than 1/2 a day's worth)

Label-reading tips

Some manufacturers now list the omega-3 content on the can. The total omega-3 sometimes includes ALA, which is not as useful. When DHA and EPA are listed, add these together to get the total long-chain omega-3 content.

Remember, your daily target is 430mg for women and 610mg for men. Some manufacturers may label in grams rather than milligrams: 0.1g = 100mg.