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Long-chain omega-3 fatty acids in red meat.

Article Excerpt
KEY POINTS

* Newly introduced Nutrient Reference Values indicate that most Australians need to increase their dietary intake of the long chain omega-3 polyunsaturated fatty acids (LC omega-3 PUFA), viz. eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA), to reduce the risk of chronic disease.

* Analysis of the 1995 National Nutrition Survey revealed that meat contributed almost as much as seafood to the LC omega-3 PUFA intake of adult Australians.

* Meat has a relatively high content of DPA, relative to EPA and DHA. Thus DPA accounts for 29% of the average LC omega-3 PUFA intake of adult Australians.

* Recent evidence suggests that DPA is just as important as EPA or DHA for delivering the health benefits associated with LC omega-3 PUFA.

* Current regulations, however, do not take account of the DPA content of foods in determining whether they qualify for an omega-3 content claim. Moreover, the DPA content of foods will not be considered in a proposed general level omega-3 health claim.

* Lean red meat is an important natural food source of LC omega-3 PUFA, the content of which can be influenced by modifying the composition of livestock feeds.

INTRODUCTION

For more than a generation, Australians have been advised to reduce their consumption of saturated fat in order to reduce the risk of coronary heart disease. Animal fat, the predominant source of saturated fat in our diet, has been targeted, resulting in the widespread introduction and adoption of reduced fat products such as skimmed milk and trimmed cuts of meat. At the same time, there has been an increasing awareness of the distinctive qualities of unsaturated fats and, in particular, an appreciation of the relative attributes of monounsaturated fat as well as the omega-6 (n-6) and omega-3 (n-3) classes of polyunsaturated fat (PUFA). It is now apparent that, with the exception of trans fats, all unsaturated fats, when consumed regularly, have the potential to improve fasting blood lipid levels. (1) However, there are important differences between classes of unsaturated fat and their effects on blood lipids and cardiovascular (CV) risk. Unlike monounsaturated and omega-6 polyunsaturated fats, omega-3 fatty acids do not lower LDL-cholesterol but they lower fasting blood triglyceride levels and they can also inhibit clotting, facilitate blood flow and help to maintain a healthy heartbeat. (2-4) Thus they offer a multifactorial approach to counteract cardiovascular disease.

THE NEED FOR LONG CHAIN omega-3 PUFA

Subtle differences in molecular structure distinguish omega-3 from n-6 fatty acids (see Fig. 1). These structural differences confer important differences in biological activity on these molecules. As both these classes of PUFA mediate physiological functions yet neither is synthesised in humans nor are they interconvertible, each is considered to be essential for human diets. (5,6) Linoleic acid (LA), an n-6 fatty acid, and to a lesser extent [alpha]-linolenic acid (LNA), an omega-3 fatty acid, are both abundant in plant foods. As precursors for the synthesis of the physiologically important longer carbon chain n-6 fatty acid, arachidonic acid (AA), and the long chain omega-3 (LC n-3) PUFA, eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA), respectively, LA and LNA were thought to fulfil the dietary requirements to deliver these...