Confused about fried foods

I have read (in Andreas Moritz book) that body needs good fats like Olive Oil, Coconut Oil, Butter & Ghee. This is because fats keep the bile flowing and hence prevent the formation of gall-stones. Ppl who fast, or follow a low fat or no fat diet are at high risk of forming gall-stones.

So why is deep-fried food not healthy? I am talking about home deep-frying not restaurant stuff. If we deep fry at home with healthy fats, shouldn't it be fine?

Or is it the heat which destroys the health benefits of healthy fats?

Any insights?
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