The role of fat in the body PART 3
If the 2002 vegetarian magazines still recommends oil frying, then I am afraid that has to be sacrificed another generation or two, until the ignorance will disappear from among those who give advice to others.
If, decades ago, grease thermal maltreatment occurred mainly in households, today the frying is the fastest and economical way of food preparation in food industry also. It’s known that at least half of the consumed food in restaurants and canteens contain deep fat components. A considerable amount of fat is in the respective food; eg. fries potatoes absorb 8-12% fat and potato chips 40-45%.
First, we should always keep in mind that market oils have already been subjected to heat treatment twice, up to 428- 4532 F, once in the extraction process, and the second time with the refining, to withstand for one or two years on the stores shelves. During the refining process increases the level of oxidized triglycerides and fatty acids TRANS. All these thermal oxidation are harmful for health.
We also should not forget that this oil, twice maltreated, it is also hydrogenated and is added a series of chemical substances to be converted into margarine, which then we fry again in the pan or in the oven.
Heating edible fats, which occurs during baking or frying, leads to numerous changes in their structure. Some authors could identify up to 211 volatile compounds in the heated oils.
Under the influence of high temperatures, greases and oils are susceptible to oxidation with formation of hydroperoxide. Due to their high reactivity, these hydroperoxide react very quickly to form the secondary oxidation products (particularly at high temperatures), such as aldehydes, ketones, epoxy, hydrocarbon, and cyclic compounds that have toxic and carcinogenic properties.
As a result of the oxidation reactions that occur, free radicals that can attack the deoxyribonucleic acid are formed, ie genetic material.
Heating the fats can also lead to dimerization or polymerization of unsaturated fatty acids or triglycerides. In addition, steam that is produced when food is fried with a specific humidity, can produce hydrolysis or triglyceride lipolysis with the formation of free fatty acids, mono and diglycerides.
Also during the fats heating increases the fatty acid TRANS content by the isomerization of CIS acids. Others products of the fats heat treatment are conjugates fatty acids. Thus, in the refining of edible oils are formed conjugates octadecatrienoic.
Nutrition Physiology Laboratory researchers from Paris-Sud University, have shown (Journal of Nutrition 2000; 130: 1524-1530) that the frying of oils and their industrial refining lead to the formation of cyclic fatty acid monomers that perturb different lipid metabolism processes. Their administration to mice caused an increase in the mortality rate and a poor development.
Even mice newborn, which were fed with acids resulted from the oil frying and refining showed a higher rate of deaths than in the control group. Adding these acids in the myocardial cell culture altered their physiological properties.
Frying lower your fat nutrition value, as a result of essential polyunsaturated fatty acids decomposition, to form alteration products – polymer triglycerides. The amount of oxidised triglycerides increase significantly after each frying.
Heated oils and fats undergo autoxidation process, and the autooxidation intensity it is proportional to the degree of fats unsaturation and with the presence or the absence of substances that favors or breaks the oxidation. Animal fats suffers the autooxidation faster than vegetables origin oils, even if animal fats are saturated. This is due to the lack of natural antioxidants in the animal fat.
When heating oil, the biggest termooxidative alteration take place with polyunsaturated fats. Thus, a fatty acid, three times unsaturated, ie three double links, undergoes the autooxidation process 10,000 times easier than an monounsaturated fatty acid. Recall that 60-70% of fat in the sunflower oil, corn germ or soy are fatty acids with two and three double links. In contrast, 70% of fats from olive oil are monounsaturated.
If we heat animal fats, polyunsaturated oils and even monounsaturated fats for a longer time at 3272 F, the animals fed with these fats will present severe liver damage. Let’s not forget that the oil bath for potato fries in restaurants stands on the fire a whole day, and the remaining oil is used in the next days.
The lipid peroxidation with the substrate of polyunsaturated fatty acids, is involved in the etiology of cardiovascular diseases, the neoplastic as well as those degenerative, and also the acceleration of aging. Not long ago, was very discussed that the polyunsaturated fatty acids decrease the circulating cholesterol concentrations. It was later observed that the decrease is also due to HDL useful fraction diminish. Now it is known that polyunsaturated fatty acids increase the cholesterol synthesis in comparison with monounsaturated fatty acids oil. (American Journal of Clinical Nutrition, 1997; 66: 438-441, no. 2 August 1997).
So, to remember that, as a molecule has more double links, the easier occurs peroxidation with the formation of free radicals. In natural state fats – nuts, seeds, olives, avocado, vegetables – is free radical formation is, largely, prevented due to natural antioxidants, which are found in those foods.