In the 1990s, proponents of the low-fat diet craze insisted that dietary fat – particularly saturated fats – led to; obesity, coronary heart disease, cardiac arrhythmia, and several other medical complications.
By now, most people are aware that fats are an important macronutrient. We know that omega 3 fatty acids can actually reduce the risk of heart disease, improve cholesterol, and benefit people who have hardening of the arteries or high blood pressure. Some of us may even know that there are three types of fat – saturated fat, unsaturated fat, and polyunsaturated fat – and that we should aim for a balance of all three fats in our diet.
What many of us don’t know, however, is that not all fats are suitable for cooking at high temperatures and that we should vary our fats based on the foods we’re preparing.
Since the low-fat craze died down and people became more aware of the need for dietary fats, one oil became increasingly popular – olive oil. We see it in recipes for everything from broiled salmon to sauteed spinach. Although olive oil is a great addition to a person’s diet, there is one problem with some of these recipes – the oxidation of the oil at high heat.
The sciency bit:
Oil oxidation does not actually involve oxygen. It involves chemical reactions (removing an electron from an atom or molecule) that degrade the quality of an oil, producing a rancid odor and flavor. According to a USDA article regarding lipid oxidation, “Oxidation of unsaturated lipids [fats] not only produces offensive odors and flavors but can also decrease the nutritional quality and safety by the formation of secondary reaction products in foods after cooking or processing” (Frankel, 1980, p. 1).
What does oil oxidation actually do?
It creates “free radicals” that raise our risk of medical problems like heart attacks and cancer. Now, I don’t want make this sound like a doom and gloom “you’re going to die” type of article. The science behind this isn’t 100 percent consistent, and it is more likely that you would see harmful effects from cooking with vegetable oils or fish oils. But the bottom line is that free radicals are bad, and reducing your consumption of oxidized oils is probably a good thing.
How can we determine which oils (fats) we should use for cooking?
Several measurements of oxidation exist including iodine absorption value (IV).
The number assigned to a particular oil represents the number of double reactive bonds – basically indicating that an oil with a high number has more double reactive bonds and requires more care to slow the process of oxidation. To give all of this chemistry some real-world application, let’s look at the IV of some popular oils.
According to the International Union of Pure and Applied Chemistry (1990), the iodine value of olive oil is about 80; whereas, the IV of coconut oil only is only about 10. This range extends even farther with sunflower oil coming in at about 130 and sardine oil at about 185.
So, what can you do to reduce oil oxidation?
Oxidation can be influenced by several factors including light exposure, oxygen exposure, and temperature.
- Store your oils in air tight containers (to prevent oxygen exposure), and if your olive oil came in a dark green or brown bottle, don’t transfer it into a clear container at home (light exposure).
- Consider cooking temperature when choosing your oils.
- For high heat, try saturated fats like coconut oil.
- For low heat recipes or salad dressings, use olive oil.
In addition, we can use antioxidants to help
So, think about oxidation of oils and consider that an herb like rosemary is considered an “antioxidant.” Cooking your meal with rosemary can slow oxidation of your cooking oils. Try roasting your chicken, sweet potatoes, and veggies. Use rosemary on the grill – shrimp kebabs, asparagus, and onions.
Want to know more about cooking with oils? Comment below!
Frankel, E.N. (1980). Lipid oxidation. Northern Regional Research Center, U.S. Department of Agriculture.
Volume 19, p. 1-22. Retrieved from: naldc.nal.usda.gov/download/25421/PDF
Pocklington, W.D. (1990). Determination of the iodine value of oils and fats. International Union of Pure
and Applied Chemistry. Vol. 62, No. 12, p. 2339-2343. United Kingdom.
Image retrieved February 7, 2016 from http://www.glutenfreeclub.com/cooking-coconut-oil/