Photo Source: http://www.webmd.com/diet/omega-3-dha-11/slideshow-omega-3-shopping
Most of the common vegetable oils, such as corn, soybean, canola, sunflower, safflower (or just the generic vegetable oil — usually canola that you buy at the store) and others that are commonly used for cooking are largely composed of polyunsaturated fatty acids (PUFA).
PUFAs are just what they sound like: fatty acids with two or more double bonds in the carbon chain that makes up the backbone of fatty acids. The two essential fatty acids, alpha-linolenic (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid), are PUFAs. While these fats are required for proper function as G. Burr and M. Burr discovered and reported in 1929, PUFAs can also be harmful if consumed improperly.
Effects of Heat
PUFAs are unstable at room temperature where they oxidize when exposed to light and moisture in the presence of oxygen. The oxidation is exacerbated when you add heat to the equation. When PUFAs become oxidized, they create free radicals which react with your cell membranes. The membranes of our cells are composed of unsaturated lipids that are similarly unstable like the polyunsaturated fatty acids.
Free Radicals and Aging
Free radicals have also been linked to aging. When the mitrochondrial DNA reacts with free radicals, it becomes damaged and cannot be repaired like nuclear DNA can. As a result, the damage accumulates and eventually shuts down the mitochondria of the cell. Since the mitochondria are the major producers of ATP (or the energy transporters of the cell), when the mitochrondria shuts down, the cell eventually shuts down as well. This cell death leads to aging.
Getting Essential Fatty Acids
Omega-3 fatty acids are essential to the body, and because we cannot form them internally, we need external sources. Polyunsaturated fatty acid oils can be used for dressings while remaining relatively stable. These oils should be purchased in dark glass bottles and come from a cold-pressed source. They should be stored in air-tight containers in a refrigerator or freezer. Don’t use these oils if they smell bad as that means they have become rancid.
Polyunsaturated fatty acids are the most stable in their whole form. Consuming flax seeds instead of flax seed oil helps prevent radicalization. Also the flaxseeds contain antioxidants that are lost in the oil and can help protect from oxidation. Omega-3s can also be found in greens, walnuts, mustard seeds, squash, and cauliflower to name a few.
So What do You Cook With?
While polyunsaturated fatty acids are unstable, the less unsaturated the fatty acids become, the more stable they become. Olive oil contains mostly monounsaturated fatty acids, fatty acids that contain only one double bond. This allows for less reaction sites for oxidation to occur.
Saturated fats are the best for cooking, however, as they are the most stable containing no double-bonds and therefore are the best to use in cooking. Coconut oil and palm oil are good plant sources of saturated fat.
So the next time you’re looking to stir-fry those veggies, grab some coconut or olive oil. If you are looking to add that Asian flavor, add the sesame oil after cooking.