Couples decades ago all fried on oil "with a smell" which wasn't exposed to cleaning. Most of people also didn't know other vegetable oil. Now there is an opinion that can't be fried on such oil. The choice of oils in grocery stores became very broad presently. And now it is possible to meet often the insistent recommendation that it is necessary to fry only on the cleaned, purified oil. And to use unrefined oil in salads and other ready-to-eat meals.
At first we will be defined for what such recommendations are made. They are given, as a rule, in order that our food was useful. In that case, about frying of the speech shouldn't be, in principle. Because what oil wouldn't be at high temperatures it emits hazardous substances. And the distinction of properties of oils when frying, whether it be refined, or not refined, doesn't play a large role.
When frying, transfats are formed. It, in turn, leads to obstruction of vessels, atherosclerosis. Atherosclerosis not the only threat of the use of products after frying. Also there can be Alzheimer's disease, Parkinson's disease and oncological diseases.
Most of hostesses of the house doesn't reuse oil. And here if the speech about production commercially or about institutions of public catering, then there the situation is absolutely differently. And in that case, the products which underwent processing on oil which is used repeatedly turn out toxic and very unhealthy.
The difference between home-made food and products of a public catering is considerable. But anyway the food which underwent frying process isn't healthy. If we speak about process when on food the ruddy, golden crust is formed, then it is, undoubtedly, about high temperature. When oil raskalivatsya to so high marks, mutagens which harmful influence DNA of cages are formed.
Quite another matter, if we speak about such ways of cooking as suppression, languor or cooking together with oil addition. Because at a low temperature, to hundred fifty degrees, the useful acids which are contained in oil don't collapse and carcinogens aren't formed. If temperature is higher, then hazardous substances are emitted. Also there is no difference what oil at the same time to use.