fishy facts and omega-3 fats

The past decade has had many contenders for the title of “superfood” and while there will never be an agreement as to which should get the crown – fish is certainly a finalist. We are told, it is rich in health giving anti-inflammatory oils and provides protein without the so-called bad fats abundant in land animals. The biggest selling point for seafood is that is contains the long chain omega -3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic (DHA).

What’s so important about omega-3 fatty acids?

This is an essential fatty acid, meaning that our body needs it to survive – like vitamins but unfortunately we can’t make it, so have to rely on getting it from our diet. Omega-3 fats build hormones, are a vital anti-inflammatory chemical and are implicated in the prevention of many serious health problems such as heart disease, asthma, arthritis and even psychiatric conditions to name but a few. These fats are also essential nutrients for babies and children’s nervous system development and are also highly concentrated in the retina of our eyes.

While some plant foods, especially nuts and seeds, a good sources of omega-3’s this is in the form of alpha-linolenic acid (ALA) a short chain fatty acid, which the body then needs to convert to DHA and EPA to do all the good stuff. There are many complicated biochemical factors to make this occur and without a variety nutrients (including Vitamin E, B6 and zinc) and enzymes (that our body has less of as adults) ALA may end up creating inflammatory prostaglandins which could be involved in diseases such as some cancers and other serious conditions.

The omega-3 picture gets even more complicated by it’s relationship with another fatty acid, omega-6. Omega-6 fats are also implicated in some circumstances, by creating inflammation so when looking at fatty acids the greatest benefit comes when there is a higher ratio of omega-3’s to omega 6’s.p

Do all fish have good amounts of DHA and EPA?

Shellfish are not known to be particularly high in long chain omega-3’s however a standard serve of (see analysis below) some mussels and oysters have been shown to have a fair amount but prawns are comparatively lower.

It is widely acknowledged that the best source of long chain omega-3’s come from deep sea, fatty fish. According to the Choice study, the best fish sources in Australia to give about 500mg of EPA and DHA per serve, include:

Gemfish
Mackerel
Mullet
Oreo dory
Sardines
Swordfish
Trevally
Atlantic salmon (though this may be debatable depending on what farmed fish are raised on)
Bonito (study done on fresh fish rather than dried flakes used in Japanese cooking)

Other fish will have lower levels of DHA and EPH and are still a good source of protein and other nutrients.

What about tinned fish?
Tinned mackerel, pink and red salmon and sardines are good sources of omega-3’s, though not always tuna – the most widely eaten tinned fish in this country.

The tuna issue is interesting. The omega-3 content can be variable and it is not primarily the canning process to blame for this. Other fish are tinned in a similar, high heat process and seem to be reliable sources of long-chain omega-3’s.

The following extract from the Omega-3 Centre website attempts to explain the variations of EPA and DHA levels in tinned tuna.

There are at least 7 good reasons for the variability of Omega-3s in canned tuna

1. There are different species of tuna with different levels of Omega-3s
A CSIRO analysis indicates, for example, that Yellowfin tuna contains 114mg EPA and DHA (the long chain Omega-3s) per 100g and Southern bluefin tuna contains 219mg EPA and DHA*.
2. There are seasonal variations in tuna's Omega-3 content
The age of the fish will make a difference too.
3. Different canning plants use different methods to clean and cook tuna
The cleaning and cooking process prior to canning may cause some oil to be lost from the fish. This oil, which contains Omega-3s, used to be simply discarded or burnt as fuel but nowadays this valuable resource is often collected, refined and re-enters the food supply. Note that there is no deliberate removal of Omega-3s in the canning process.
4. The Omega-3 rich part of the tuna - the dark meat - may not be included in canned tuna
Many consumers do not like the look or taste of the dark tuna meat so manufacturers do not include this part in specific canned tuna products. The amount of Omega-3 rich oil can vary 5-fold depending on which part of the tuna is analysed.
5. Tuna may be sliced or, cut into chunks - this can affect how much Omega-3 is lost
The greater the surface area, the greater are the likely Omega-3 losses.
6. The Omega-3s in tuna canned in oil can dissolve into the oil and are lost when the oil is drained off
7. The analytical method to identify the levels of long chain Omega-3s is difficult and requires specific types of equipment

Check the label of canned fish and other foods that you think may contain the important Omega-3 nutrients to compare how much is actually there. If there is no listing in the Nutrition Panel on-pack it could mean the product has none or few Omega-3s.
* Nichols PD, Virtue P, Mooney BD, Elliott NG, Yearsley GK. Seafood: The good food. CSIRO Marine Research, 1998

Is frozen fish a good source of omega-3’s?

A Choice study (2005) of frozen fish fillets available in supermarkets found most were from white, low omega-3, fish such as hoki. The low omega-3 content was not because the fish was frozen, rather because most did not use oily fish. The study also noted, when price per gram was taken into account – it would usually be cheaper to eat fresh fish instead.

Can you get long-chain Omega-3’s from other sources?

There are now a number of enriched foods, mostly baby foods, yoghurt and bread on the market.

From the Omega Centre – amounts of omega-3’s in common foods.

Total long chain Omega-3 content of some common foods
Seafoods mg/100g
King salmon *
Greenshell/lipped mussels 950 #
Hoki (Blue grenadier) 410
Gemfish 400
Blue eye cod 310
Sydney rock oysters 300
Tuna canned 230
Snapper 220
Barramundi saltwater 100
Giant tiger prawn 100

Eggs regular 80
Turkey 30
Beef 20
Milk regular 0
Cereals, rice, pasta, etc 0
Vegetables 0

Source: Fatty acid database, RMIT University _* Massey University analysis _# NZ Crop & Food analysis_^ Check labels of Omega-3 enriched foods

NB: omega-3’s vary in both type and quantity in eggs. A free ranging chook who eats greens and worms will produce a more nutritious egg.

Grass raised red meat are better sources than grain fed animals.

How much omega-3 do we need?

The standard recommendation for women is 90 mg/day and 160 mg/day for men, however authorities like the Omega-3 Centre suggest for disease prevention and treatment it is more like 430 mg/day for women and 610 mg/day for men.