I've had a few friends ask for my opinions on oils - specifically about different uses for different oils, as well as the health claims that certain oils have made. As I've been working on pulling my thoughts together, I have discovered just how many bits of information, misinformation, uproar, and strong opinions exist out there on this subject! It is my goal to give you the best information - by that I mean the most unbiased and research-based - that I can find.
First, let's point out that we are talking about OIL and not just the generic FAT. I make this distinction to help push you towards choosing fats that are LIQUID at room temperature. Fats like butter, lard, and shortening are primarily saturated fat, and have been linked to heart disease. Now, some recent research has put this into question. But I would say, not enough to throw caution to the wind :)
So back to oils. One of the major distinctions of oil is how the oil is separated from the rest of the food. Pressed (hot or cold) and chemically extracted are the big two. Pressed means that the oil is removed using mechanical pressure (just like it sounds). Cold pressed indicates that the whole process is done relatively slowly and doesn't produce a lot of heat (primarily this would occur from friction). It requires a soft food, like olives or walnuts. Hot pressed is used for harder foods - maybe a little steam to soften up the food and make it suitable for pressing. Other foods require chemical extraction, which is done in larger-scale situations. It involves chemical solvents, removal of the chemicals, and often bleach. This process provides the oils with a longer shelf life.
From that basic description, it seems pretty clear that choosing an oil that is pressed is going to be better for you than one that is chemically extracted. And cold pressed tends to be preferred over hot pressed.
In addition to that, you can find both refined and unrefined oils on the shelves of your local grocery store. Unrefined oils are only filtered lightly - this removes large particles, but not the fine sediment. These oils tend to have bolder color, flavor and fragrance. They tend to have a shorter shelf life than refined oils. Refined oils have been filtered and strained more than their unrefined counterparts. There may be additional heat involved, but it is not a chemical process. These oils have a longer shelf life.
Notice that at this point, I haven't really mentioned specific foods or origins of the oils. So far, it's been all about the process. This is important because you can find - for example - olive oil that has been cold pressed or hot pressed, refined or unrefined. Simply stating "olive oil" isn't enough to understand the health benefits or when to use it.
Another defining characteristic of oils is the smoke point. The smoke point is the temperature at which the oil begins to smoke - anyone who has experienced a smokey kitchen knows that this is not a desirable situation to be in! The smoke point is also when an oil begins to break down and produce free radicals and potentially cancer-causing substances. As I said, you want to avoid this situation.
In general, the lighter the oil, the higher the smoke point, or the better an oil is for high-heat cooking. Lower smoke point oils are best for marinades, dressings, or cold dishes. Here is a list of some common oils and their smoke points.
As you can see, there is no one-size fits all answer to which oil is best. I like to keep a variety of oils on hand for different purposes. Right now, I have extra virgin olive oil, canola oil, walnut oil, peanut oil, coconut oil, and sesame oil all in the house.
Stay tuned for more on oils in future posts!