Found mostly in animals, saturated fats have high melting points and are typically solid or nearly solid at room temperature and in bodily membranes. Coconut and palm oils are also saturated fats.
The typical example of this type of fat -- sometimes called omega-9 fats -- is olive oil. These fats have lower melting points and so are liquid at room temperature, but they will solidify a little or go cloudy in the fridge.
Polyunsaturated fats have the lowest melting points and are liquid at room temperature and in the fridge. Many are what we call essential fatty acids – they’re vital for normal bodily functions but cannot be manufactured in the body.
Essential Fatty Acids: Omega-3
The omega-3 fatty acids are typified by fish oil and flaxseed oil.
Essential Fatty Acids: Omega-6
The omega-6 fatty acids include all the familiar cooking oils, namely sunflower oil, safflower oil, corn oil, and so on. These so-called 'cooking oils' are in fact very poor foods and should be avoided altogether in cooking.
Trans-Fatty Acids and Other Altered Fats
Mechanical and chemical processes that convert nut or seed oil extracts into tasteless, odorless oils produce so-called refined oils, which are best avoided.
Other processes are used to create a variety of unnatural compounds, including trans fats, and partially and fully hydrogenated vegetable oils.
Because these altered fats make cell membranes even more rigid and dysfunctional than saturated fats do, they are to be avoided at all costs.
This means no margarine, pies, or biscuits, and particularly no fast foods like French fries.