>Latest evidence is that oils identified as "healthy" such as sunflower or corn oil, produce "aldehydes" when heated. Aldehydes have causative links to cancer and other disease with levels up to 200 times as high as the "safe" dose in fried food. Whereas butter and even lard have much lower levels of aldehydes when heated. Olive oil has lower aldehydes and remains a safe option, or avocado oil if you can get it.
We cook practically everything on lard; some of it on palm oil and sometimes olive oil, when the recipe calls for it. Butter - yes, spread on bread. Haven't bought margarine for I can't remember how many years.
Those refined oils... we did use them for a number of years because they convinced us they were "healthier" (whatever - all food is dead, can't be healthy). Stopped that some time ago.
And guess what, I have only 3-4 kg more than when I was a student.