The use of oil in the frying of food
The frying of food in oil or lard also has detrimental effects. Studies have shown that heated oils and fats undergo autoxidation and that the rate of autoxidation is proportional to the degree of unsaturation and the presence or absence of pro- and anti-oxidants. It has been established that animal fats undergo autoxidation more readily than oils of plant origin, in spite of the fact that animal fats are saturated fats, but this has been attributed to the virtual absence of natural antioxidants in animal fats. Polyunsaturates, however, sustain the most thermo-oxidative damage when oil is heated. In this regard it is enlightening that a tri-unsaturated fatty acid will undergo autoxidation 10 000 times more readily than a monounsaturated fatty acid.38 The rate and degree of autoxidation of unsaturated and saturated fats is presented in figure 3.10
Figure 3.10. Heat damage sustained by oil. (Adapted from reference 20)
The products formed in fats and oils that are heated to high temperatures are peroxides, aldehydes, ketones, hydroperoxides, polymers and cyclic monomers, any one of which can have toxic effects. Subjecting saturated and polyunsaturated fats, such as butter and sunflower oil to temperatures of 170°C for two hours will so alter the composition that if fed to experimental animals they will induce liver ailments in these animals. If animal fat, polyunsaturated oil, and even monounsaturated oil such as olive oil, is however heated to 180°C for longer periods of time, serious liver disorders are induced in experimental animals that are fed these oils.39 The peroxidised fatty acids in heated fats also affect the cardiovascular system, possibly even causing lesions in the cardiac muscles and arterial lining as well as enhancing clot formation.40
As most processed oils are heated to 220°C during the manufacturing process, and are still further heated during the frying process, the use of free oil should for these reasons alone, not be encouraged. The frying of food should therefore be avoided if healthful living practices are introduced into the household. This does not necessarily mean that taste must be sacrificed, but it does mean that age-old habits will have to be revised and substituted with a little bit of ingenuity. If oil is used at all, it should be used in moderation and the cold-pressed variety should be used as this has been least subjected to heat during the extraction and clarifying processes. Also oils rich in monounsaturated fats, such as olive oil, should be the oils of choice as monounsaturated fats undergo the least damage during heating.
Whilst it is true that increased dietary consumption of polyunsaturated fats has led to a decrease in cholesterolaemia and associated drop in cardiovascular disease, it has been accompanied by a rise in deaths from nonvascular diseases such as cancer,41 cholelithiasis42,43 and a general drop in life expectancy,44 probably resulting from the peroxidation of the polyunsaturates. Peroxidation of polyunsaturates takes place because these molecules are unstable, and the more double bonds there are in the molecules the more readily the process of peroxidation takes place. During this process “free radicals” are formed which are extremely reactive in view of their unpaired electron. Free radical formation is largely prevented in whole foods, as natural antioxidants, which are present in these foods, prevent their formation. A natural balance exists between antioxidants such as the fat-soluble vitamins A and E and the quantity of polyunsaturated fats that are present in whole foods. An imbalance between polyunsaturates and antioxidants will result in a rise in free radical formation with concomitant harmful results such as an increase in the rate of the aging process,44,45,46 inflammation,47 carcinogenesis,48,49,50 liver disorders51 and arteriosclerosis.52,53
Unfortunately modern food processing techniques often strip food of the essential fatty acids and vital prepacked antioxidants and in this way deprive the system of these essential nutrients. During the refining process grains, for example, are stripped of the germ, which contains the essential oils and fat-soluble antioxidant vitamins in a perfect biorelationship, and the lack is then substituted for with large intakes of disproportionate combinations of processed oils and fats. In this regard it is enlightening to note that the daily vitamin E requirements (which amount to about 10mg per day) increases 200 fold if polyunsaturates are added to the diet.53 It is doubtful whether any diet will supply this additional requirement without supplementation, and it is therefore not surprising that the degenerate diseases are so prevalent in Western societies. The eating of whole foods that have not been stripped of their essential components will supply all the essential oils required in healthful combinations and should therefore be encouraged.