When it comes to frying oils, we can’t complain about the lack of available alternatives. Large supermarket shelves are full of options.
But this variety of alternatives can be extremely confusing, given the great debate that exists about the benefits and risks of consuming different types of oils.
You might think that frying with vegetable oils is healthier than cooking with animal fat like lard or pork. When frying or cooking at high temperatures (around 180 C) there is a change in the molecular structures of the oils and fats that are used. They undergo a process called oxidation, whereby they react with oxygen in the air forming aldehydes and lipid peroxides, which are very harmful to health. At room temperature, something similar happens, but much more slowly.
When lipids go rancid, they too become oxidized. Oxidized oil is very bad for health, almost poisonous. Never leave a bottle exposed to light, the oil will oxidize over time. Note that expensive oils come in dark bottles.
Sunflower oil and corn oil are fine as long as they don’t heat too much, no more than 170º, such as for frying or cooking. Olive oil generates much less aldehydes and is the most recommended.
Anyway, if you don’t have olive oil, which is more expensive, any medium-quality oil will do, as long as you don’t overheat it.