But, before you go throwing any old fat into the pan, you probably should know that all oils are not created equal. There are some you should cook with, some you shouldn’t, and some you should probably never eat again.
“Saturated” means “stable”
We now know that saturated fat is not the silent killer it was believed to be for the last half-century. In fact, saturation is not only not dangerous, it’s downright beneficial. Here comes the science: A fat is monounsaturated if it has one double bond within the fatty-acid chain. A fat is polyunsaturated if it has more than one. Saturated fats have no double bonds. What does that mean? The more double bonds, the more vulnerable the fat is to oxidation, which happens when the fat is exposed to light, air, and especially heat.
When it comes to cooking, “The first thing you need to know is degree of saturation,” saysDr. Cate Shanahan, MD, author of Food Rules: A Doctor’s Guide to Healthy Eating, and Nutrition Director for the Los Angeles Lakers. This is because when you cook, the more saturated a fat, the more stable and less likely to oxidize it is — making more saturated fats a better choice.
When we eat oxidized oils, we’re essentially eating radiation, say Drs. Carpenter and Shanahan. “Oxidized oils are molecularly unrecognizable by our body,” says Dr. Shanahan. “Once inside, they react with oxygen and iron in our blood and spark free-radical cascades.” In her book, Deep Nutrition: Why Your Genes Need Traditional Food, Shanahan explains that these molecules can harm other cells they come in contact with once inside the body. This damage is otherwise known as inflammation, which has been linked to issues from arthritis to food allergies to IBS to cancer, heart disease, and stroke.
Furthermore, “You are what you eat,” says Dr. Carpenter. Not only can eating oxidized fats cause serious damage in the long run, as some of these fats are stored for energy, others are immediately incorporated into our cell membranes, which are made up of fat. If you eat bad, oxidized fats, your cell membranes could also contain these oxidized lipids. It’s possible that these abnormal lipids could cause problems with cell function and cell-to-cell communication.
If you’ve ever seen a cooking-oils list, you’ve probably seen the term “smoke point.” But, “smoke point is irrelevant,” says Dr. Shanahan. “It’s the protein that’s burning, but depending on the fatty-acid profile of the oil you’re cooking with, you will get degradation (oxidation) long before it starts to smoke.” Additionally, and perhaps more importantly, oils that are super-refined will have no smoke point — but that doesn’t change their fatty-acid profile. So, cooking with refined, polyunsaturated oil, such as canola, is even more dangerous due to the fact that you can expose it to heat for long periods of time (making it increasingly more oxidized) and it will never smoke to warn you of the danger.
By “vegetable” oils we mean refined, polyunsaturated oils: corn oil, cottonseed oil, rapeseed (canola) oil, sunflower oil, safflower oil, and soybean oil. According to Drs. Carpenter and Shanahan, you might just want to never eat these oils again, ever. Not only are these varieties highly unstable, they oxidize easily, and the very process used to make them causes oxidation. Because it’s difficult to extract oil from a cottonseed or a rapeseed — as opposed to naturally oily things such as olives or avocados — the creation of these oils usually involves high heat and chemical solvents. (If you’re really interested, you can watch exactly how canola oil is made here). So, straight out of the bottle, you’re already getting oil that’s been oxidized to some degree — before it ever even hits the pan.