Frying process in the relation fat/degenerative diseases

Among the various components of the diet, fat receives very dose attention because of its relationship to several chronic degenerative diseases (CDD). Currently most of the available information on these relationships is derived from epidemiologic or experimental studies in which lipid intake is calculated using food composition tables. In most of these tables the quoted lipid content is that of raw food, whereas most foods are usually consumed only after being subjected to several culinary processes. Often there is no indication of the type of fat used in food processing in general or in frying in particular. But as it known, in the course of these processes the lipid content undergoes important qualitative and quantitative changes and not keeping them in mind may be the underlying cause of the difficulties an the confounding results in studies trying to establish the relationship between lipid intake an health. In the Mediterranean diet, about 50% of total dietary fat is derived not from the food itself but from the cooking fat, of which only a small fraction is eaten raw (as dressings) and the greatest proportion is used in thermal culinary processes, mainly deep-frying. The scientific study of the process whereby fat penetrates into fried foods has shown the benefits of this cooking method. If the process is correctly carried out, the amount of fat ingested with fried foodstuffs is not greater than when other procedures involving fat are used (for example, sautening, stewing or canning in oil). Very schematically deep-frying is a technique that replaces a fraction of the water content of food by cooking fat. Consecuently, the fat composition of the fried lean foods will be the same as that cooking fat. The process is more complex with fatty foods, and there are not great changes in the total quantity of fat in the fried food before and after frying. However, there are notable quality changes and these depend on the concentration gradients between frying oil and food. In deep-frying the cooking fat is usually used more than once, and there comes a moment when one considers subjectively that the oil is not longer suitable for frying and is discarded. This can be of practical significance for the total lipid intake, since a not determined quantity of oil is discarded and is not ingested. Consecuently the theoretical lipid intake has been decreased and, at the same time, some compounds, included saturated fats, are eliminated from diet whit the discarded oil. For example, the lipid composition of meats is substantially improved because of the highly favorable monounsaturated fatty acids penetration into them from the frying olive oil. In of the most important features is the possibility of manipulating fat intake by reducing it and improving the quality of the fat really consumed, this is of special interest in the possible relation to degenerative diseases. These changes in the fatty acids composition of oils and foods are repeatedly seen in laboratory experiments. However, their interpretation is not easy, in part because of the complexity of the deep-frying process used in the test. On the other hand, you would have to see the results obtained in the laboratory coincide with the results at practical level as well in the households as in catering, and, in this sense, some of the first results which we are obtaining in the population of Madrid are presented in the second part of this report.