Cooking can cause alterations in food fats, especially when intense and prolonged over time.
In this case, volatile and non-volatile substances are formed such as aldehydes, ketones, peroxides, polymers, cyclic monomers, etc. which can be responsible for toxic effects on the body.
In practice, all fats are damaged by intense and prolonged heat treatments; however there is a scale of values that sees an easier deterioration of oils with higher unsaturation, such as seed oils, unsaturated bonds are in fact, as said several times, easily attacked by oxygen and this mechanism is favoured by high temperatures.
Peroxidation is much faster the more unsaturated bonds are present and, of course, the fewer antioxidant substances are present. From this point of view, extra virgin olive oil is in a particularly advantageous situation: in fact, while monounsaturated oleic acid is scarcely susceptible to peroxidation, the complex of antioxidant substances intervenes in giving it a very high resistance to thermal damage.