Your body needs lipids -- cell walls are made of them! An extremely low-fat diet increases cancer risk substantially. And some lipids are better than others. Polyunsaturated oils are easily oxidized, creating free radicals. Saturated animal fats -- well, this is debated, and there is some indication they may have been unfairly blamed for problems that are actually caused by sugar, but I still avoid them. Olive oil, being mostly monounsaturated, is the best.