Corridor Consults: Cooking with vegetable oils presents little trans fat hazard

Question: There seems to be some controversy regarding cooking with olive oil (or other oils) leading to the production of trans fats. There are indications of some oils being more heat stable and, therefore, better for cooking, leaving olive oil for dressings and post-cooking uses. Are there any studies of at what temperatures these oils convert to trans fats, and from a practical perspective, what temperatures are we achieving with low, medium or high temperature settings on the stovetop? Has anyone actually pan-fried these oils and then tested the composition? Are we fooling ourselves that cooking with olive oil is healthy? Or are we actually doing harm?—Dr. Jason Caplan, TorontoAnswer by Dr. Bruce Holub (PhD), university professor emeritus of nutritional sciences, dept. of human health & nutritional sciences, University of Guelph, OntarioCommon temperatures for pan-frying or deep-frying of food with vegetable oils typically lie between 150°C and 190°C (300°F to 375°F). Such temperatures are below the “smoke point” for common oils such as refined canola, corn, safflower, sunflower, soy or virgin olive oil, which generally fall in the range of 204°C to 232°C.Heating to temperatures that approach or surpass the smoke point may result in some significant deterioration in flavour and/or quality with visible gaseous products, which should therefore be avoided.It should be pointed out that the processing of the oil and degree of refining can significantly influence the smoke point. For example, the smoke point of an olive oil depends upon several factors including processing techniques such as filtering, the grade of the oil and other differences between batches of the commercial product. The smoke point for an olive oil may range from as low as 190°C to 216°C for a high-quality “extra virgin” olive oil up to 242°C for a “light” olive oil.High frying temperatures can generate some very minor amounts of trans fatty acids (TFA) from a vegetable oil. Common frying temperatures of 150°C to 175°C and cooking times of five to 10 minutes generate almost negligible amounts of TFA. Shorter cooking times at lower temperatures will generate even less.Caution should be exhibited with respect to reusing an oil from a deep fryer due to the risk of TFA accumulation in the oil. The high TFA content in many processed foods and fast foods from certain restaurants is due to the use of partially hydrogenated vegetable oils containing pre-formed TFA.Heating of vegetable oils containing monounsaturated and polyunsaturated fatty acids often results in the formation of small amounts of oxidation products including “mono-epoxides” via “thermoxidation,” as found in frying oils from restaurants and fried-food outlets. There is active research ongoing to determine if such oxidized fats may pose a health hazard.Want an expert opinion? E-mail your question to Medical News Editor Andrew Skelly at andrew.skelly@medicalpost.rogers.com with the subject line “Corridor consults.”

Corridor Consults: Cooking with vegetable oils presents little trans fat hazard

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