THE DETAILS: The study was designed to simulate the conditions experienced by a chef in a restaurant kitchen. A 14-ounce beefsteak was fried either in margarine (made from nonhydrogenated palm, soybean, rapeseed, and coconut oils) or pure soybean oil (which, in the U.S., is often marketed simply as "vegetable oil" ) five times in a day for 15 minutes each, during which time the pan's temperature reached a high of 572 degrees F. The researchers repeated the experiment a total of four times, twice on an electric stove and twice on a gas stove. The researchers found that both oils on both stoves released high levels of naphthalene, a respiratory irritant found in gasoline and diesel fuels that's also used in moth repellents. Soybean oil used to fry the meat on a gas stove produced the highest levels of compounds called aldehydes, which are also components of gas and diesel that can irritate your eyes and respiratory tract. And while both oils emitted ultrafine particulates regardless of stove type, soybean oil emitted the most. Ultrafine particulates are the kind of particles you breathe in heavily polluted outdoor air, and they've been linked to lung disease, strokes, heart disease, and other problems like low birth weight in babies. The authors conclude that people should limit their exposure to cooking-oil fumes as much as possible, considering that no one knows how much of an exposure an individual can have before experiencing negative health affects.
Read on to see which cooking oils are best for your cooking needs.
WHAT IT MEANS: This study was intended to measure occupational exposures to these chemicals, so frying a beefsteak in soybean oil probably won't leave your home kitchen feeling like the L.A. freeway during Friday rush hour. But cooking oils used at very high temperatures can expose you to some pretty nasty stuff. The International Agency for Research on Cancer has classified their fumes as "probably carcinogenic to humans," and a number of other studies have demonstrated that they can pollute your indoor air. The same authors of this new study conducted similar research last year in which they analyzed pollutants released by margarine, soybean oil, virgin olive oil, and rapeseed oil during cooking. (Rapeseed oil is similar to canola oil, though they're not the same thing; farmers bred the less desirable characteristics out of rapeseeds to create canola seeds, from which canola oil is made.) That study found that rapeseed and olive oils still emitted aldehydes and particulates, but at much lower levels than margarine and soy oil. Another study of oils used in traditional Taiwanese cooking—safflower, olive, coconut, mustard, vegetable, and corn oils—found high levels of polycyclic aromatic hydrocarbons, compounds that could increase your risk of certain types of cancer.
The best way to protect yourself against unwanted air pollution is to use your stove's vent fan. The Taiwanese researchers noted that levels of pollutants decreased by 75 percent when vent fans were turned on. Also, use oils that are intended for the temperature at which you plan to cook. Read labels and look for "smoke points" or some other indication that an oil is intended for low, medium, or high-heat cooking.
Here's a short list of the best oils and their heat tolerances:
• High heat (445 to 520 degrees F): Refined versions of almond, avocado, high-heat canola, high-heat safflower, and sesame oils
• Medium-high heat (360 to 425 degrees F): Refined grapeseed, soy, coconut, and walnut oils and unrefined safflower oil
• Low to medium heat (280 to 350 degrees F): Unrefined versions of corn, peanut, coconut, and sesame oils and all types of olive oil.