The natural oils
A J Sinclair
Department of Food Science, RMIT University, GPO Box 2476V, Melbourne, Vic. 3001, Australia
This interesting and instructive article, is an excellent introduction to the complex subject of omega-3 and omega-6 fatty acids.
Fats and Oils - A brief reference table
Prof Sinclair classifies natural edible oils as follows:
Natural Edible Fats and Oils
Animals Fish Plants
Milk, butter, cheese cod liver, herring, menhaden, coconut, palm, soy
meat fats anchovy, tuna and sardine oils cottonseed, maize,
canola, peanut, and sesame oils
Natural fats and oils are composed of Triglycerides = 1 mol glycerol + 4 mols fatty acids (FAs)
Fatty acids
*Saturated (solid at room temp)
*Unsaturated (liquid at room temp)
*Mono-unsaturated
*Polyunsaturated
Polyunsaturated FAs = Essential FAs
Omega-6 FAs (most common vegetable oils)
Omega-3 FAs (fish oils)
Omega-6 FAs = Linoleic acid (sunflower, maize, peanut oils)
Gamma-linolenic acid (Evening Primrose oil)
Omega-3 FAs = Eicosapentaenoic acid or EPA (cod liver oil)
Docosahexaenoic acid or DHA (tuna oil)
Alpha-linolenic acid or ALA (flaxseed, canola, walnut, soy oils)
Changes in FA intake
In the past 50 years, there has been a dramatic change in the intakes of some of these FAs. We are all aware of the fact that western populations have increased their intake of saturated FAs to the detriment of cardiovascular health. What is less well known, is the fact that intakes of omega-6 FAs have also risen dramatically thanks to the increased use of margarine, mayonnaise, salad dressings and vegetable oils for cooking purposes and in salads. This increase is the result of the encouragement the general public are given by health professionals the world over, to replace saturated fats with polyunsaturated fats. Unfortunately, the intake of omega-3 FAs has declined concomitantly.
The ratio of omega-6 FAs:omega-3 FAs in the diet should preferably be 1, but due to the predominance of omega-6 in "western" foods, an imbalance exists and the ratio can be as high as 25:1. Consequently, there has been a concerted effort to increase intakes of omega-3 in western countries.
Functions of omega-3 FAs
Omega-3 FAs have been implicated in many metabolic processes, such as:
* brain development and function (normal growth of the brain and neurological system before birth and for the first year of life, Attention Deficit Disorder, school performance),
* cardiovascular health (atherosclerosis, reduction in ventricular arrhythmia, reduced thromboxane A2 production, decreased blood lipids, particularly triglycerides, reduction of atherosclerotic plaques, inhibition of interleukin-a and cytokines; promotion of nitric oxide endothelial relaxation, reduced blood pressure),
* psychological disorders (depression, schizophrenia),
* anti-inflammatory function (down-regulation of the production of pro-inflammatory leukotriene species; improvement in arthritis and allergies)
* bowel disease (prevention of colon cancer, remission of Crohn's disease)
* skin disease (psoriasis)
* Non-insulin-dependent diabetes mellitus
Omega-6 and omega-3 FAs compete for receptor sites on cell membranes, so if the diet contains excessive amounts of omega-6, omega-3 FAs are not able to bind to cell receptors and can thus not carry out their many vital and protective functions.
How much DHA and EPA do we consume ?
It was estimated that the average intakes of DHA and EPA in Australia are as low as 100 mg per day. This is half of the daily intake recently suggested by the Department of Health in Britain, namely 210 mg per day.
How can intakes of omega-3 FAs be increased ?
Intakes of omega-3 FAs, can be increased by:
- Increasing intakes of fish and fish oils
- Increasing intakes of plant oils rich in omega-3 FAs such as canola and soy oil
- Using EPA and DHA supplements
- Using omega-3-enriched foods