In today’s world the appearance, texture and colour of food is often considered of greater importance than the nutrient value of such food. In an instant world we need instant food, and to avoid spoilage and financial loss, such food is often chemically manipulated to obtain all these desired effects. When the chemical nature of our food is changed so that it meets the requirements of the market place, then the risk is great that it no longer meets the requirements of the body. Our bodies are designed to interact with the environment in a highly specialized way, and any interference with this delicate balance may impact negatively on the system.
Modern oil refining techniques
Extracted oil undergoes a series of steps which adversely affects its nutritional value. Free fatty acids are removed by vacuum extraction and precipitation. Furthermore, the oil is filtered and heated to 220 oC to obtain a clear liquid. In order to obtain a less fluid oil, suitable for the production of margarine, the oil is further subjected to the process of hydrogenation, to which liquid oils nowadays are also partially subjected. This process was developed by W. Norman in the year 1900 and involves a catalytic reaction which changes cis fatty acids to trans fatty acids, thus rendering them less fluid by changing the shape of the molecules.
Polyunsaturated fats contain double bonds, and this gives rise to the possibility of cis-trans conversions. In nature, fatty acids occur mainly in the cis configuration, which means that the carbon chains on either side of the double bond are spatially arranged on the same side of the double bond, whereas in the trans configuration the chains are on opposite sides of the double bond. The cis and trans configurations of oleic acid (which has just one double bond) are presented in figure 3.9.
Trans fats do not form part of the normal diet and should not be introduced into the system as they can result in a number of biochemical changes, and together with saturated fats and cholesterol, can lead to altered membrane structure and concomitant hardening of the arteries. The essential fatty acids (linoleic and linolenic acids) also naturally have the cis configuration, and in linoleic acid the atoms are arranged in such a fashion that there is a 60o bend at each of the two double bonds, resulting in a U-shaped molecule. Trans-linoleic acid however has a Z-shape as the chains on either side of the double bond do not project into the same plane. The free use of extracted, partially hydrogenated oil, rich in linoleic acid (found in corn, safflower and sunflower oils), has been associated with cancer promotion. Linoleic acid is the substrate from which prostaglandins are manufactured, and trans-linoleic acid can result in altered prostaglandins, thus modifying the effect of these hormones or even producing opposite effects. Because leucotrines play an essential role in regulating the immune system in that they are involved in the production of antibodies and the destruction of viruses and cancer cells, it is essential that these molecules be produced from essential fatty acids that have the correct configuration so that the delicate balance and the function may not be jeopardized.
Figure 3.8. The effects of eicosanoid imbalances on various diseases. (From reference 6).
Figure 3.9. The cis and trans configuration of oleic acid.
The molecular changes found in even partially hydrogenated oils can adversely affect the relationship between the various prostaglandins as well as changing them structurally. Trans fatty acids depress serum levels of prostaglandins, and both PGE1 and PGE2 were affected in a study done on rats, presumably because linoleic acid could not be converted to long chain fatty acids in the presence of a large influx of the trans-isomer.34,35 Moreover, hydrogenated oils do not share the properties of normal unsaturated fats and will also not lower cholesterol levels as do the natural oils in whole foods.6,36 The consumption of trans fatty acids in the Western world is quite high, and it has been estimated that in the US and in Canada, men of 20-39 years of age consume 11-12g per person per day of these fats.36 The British Medical Committee on Cardiovascular Diseases proposed new guidelines in 1994 on recommended consumption of fatty acids. Recognizing that trans fatty acids have an undesirable effect on HDL and LDL cholesterol and coronorary disease mortality, they suggested that no more than 2% of caloric intake come from this source, and that the amount should even be reduced.37