I don't subscribe to that facile "eat a low fat diet" theory, which has yet to prevent cardiovascular disease, despite the recommendations by doctors. My working theory is that if you cut out the bad fats, you don't need to worry about the quantity of good fats you eat. So far, my theory is working.
So how do you know if the fats in an oil are good or bad? Foremost, I'd say you should be able to taste the fats in a good oil. This means not only that the oil should taste good, but even more importantly, that it will have a flavor at all. Unrefined oil will have a flavor at least vaguely reminiscent of the nut or seed--or fruit, as in the case of olive oil--that it came from. Refined oils have had every bit of the flavones, antioxidants, and subtle aromatics scrubbed out of them with harsh chemicals, which gives them a long shelf life--along with a ton of damaged molecules--but no nutritional value. Basically, with the exception of extra virgin olive and coconut oils, all the unrefrigerated oil on the shelves are refined; they're good for nothing but frying things in--and even then they add twisted molecules to the equation, like insult to injury.
Saturated fat has endured some rather longstanding vilification which is undeserved in some cases. It bears mentioning that every natural oil contains some saturated fat, along with mono- and poly- unsaturated fats. You may have noticed that extra virgin olive oil left in the refrigerator will solidify; that's the saturated fat content in action. That said, there are some good and some bad saturated fats. I read a helpful piece last week by David Katz, M.D. that explains this well.
As far as good fats, anyone who's been paying attention (and reading my blog) will most likely have noticed that I'm a fan of Udo's Oil, and the DHA blend in particular. The reason for this is twofold: 1) I've come to understand that my body needs essential fats, and I've been enjoying incredible benefits from using the oil in my food, and 2) of all the sources of omega-3/omega-6 I've come across, Udo's Oil offers the best quality and protects the fragile fats in all possible ways. OK, full disclosure, there's also the fact that Udo is a good friend of mine, and the oil is prominently featured in a cookbook I wrote.
When I'm cooking (as in heating oil in a pan), I use olive oil--if some water or wine is present, to keep the temperature down--or coconut oil, which is quite heat-tolerant. I almost never heat anything to the point where it browns, so there is little danger if any that the oil itself will be damaged the way refined oil has been.
I'm also a fan of Bija olive, nut, and seed oils, for some of the same reasons. Their "Old Grove Greek Olive Oil," from 600-year-old trees, is everything a good olive oil should be: fruity, delicious, with no unpleasant aftertaste (you know what I mean--that nasty postnasal-ish thing that happens right after you swallow inferior olive oil). Their seed and nut oils are pressed with something they call a "hydro-therm" process, that helps protect the integrity of the fats from excessive heat.
The flavor of these oils is incomparable. I don't know how many times I've bought walnut or hazelnut oils in specialty stores that were either rancid or borderline when I opened them, and turned far worse within days. Bija oils have a clean, fresh-off-the-press feel, with a clear flavor of the seed or nut it came from. The sunflower oil is the most pronounced--it's literally like throwing a handful of sunflower seeds into your mouth. I used the walnut oil to make the dressing for the kohlrabi and apple salad in my last post, as I do in most salad dressings when the application requires a mild flavor.
Full disclosure: I don't make a cent from the sale of any of the oils I mention (oh, if only...). I did recently receive a few complementary bottles of Bija oils (hence the photo), but I would gladly have paid if that had been the only way to get them. I do recommend them highly, but only because they work for me. Look for them at your local natural foods store. If they don't have any, ask them to special order some for you. You can also order online, or by phone, at 1-800-498-3610. Keep them in the refrigerator, by the way.