Putting the heat on cooking oil

Adding a splash of oil to your cooking can boost not only flavour but also texture. Just ask any celebrity chef (or any non-celebrity chef for that matter, if you can find one) and they will happily extol the virtues of adding oil to your cooking. The relentless, searching intellect that leads one into the realms of professional cookery will ensure that any given chef will also be able to give you a detailed rundown of the biochemical background and commensurate health implications of any recommendation that they make. Should you wish to engage in sophisticated banter on the topic of oils with one of these culinary mavins, then a new study should give you something to talk about.

The new study started from the premise that it has been previously shown that substances called aldehydes are toxic to the human body and are believed to cause some types of cancer as well as neurodegenerative diseases like Parkinson’s and Alzheimer’s Disease. It is also known that cooking at high temperatures causes aldehydes to be released from oils into the atmosphere. So what these researchers wanted to establish was whether the aldehydes remained within the heated oils to be consumed when you eat your meal.

The aldehydes in heated oils result from the breakdown of fatty acids in the oil. The aldehydes are highly reactive and can interfere with proteins, hormones, and enzymes. This is why they can have significant health effects.

The researchers used gas chromatography/ mass spectrometry techniques to measure aldehyde levels in heated olive oil, sunflower oil, and flaxseed oil. The oils were heated to 190 degrees Celsius in an industrial deep fryer for 40 hours (eight hours a day) for the olive oil and sunflower oil, and for 20 hours for the flaxseed oil. Flaxseed oil is not widely used in cooking but was chosen for its high omega-3 fatty acid content.

The results showed that sunflower oil produced the most aldehydes in the least time, closely followed by flaxseed. This is because they are high in polyunsaturated fats (linoleic and linolenic acid). By contrast olive oil which is high in monounsaturated fats generated less aldehydes and produced them later in the process.

Previous research has also shown heating olive oil produces less aromatic hydrocarbons (toxic substances) than other oils.

The bottom line is that olive oil is the best choice when using oils in heating food, at least from a health perspective. Since aldehyde production increases over time the best idea would also be to avoid reheating any sort of oil. As Popeye could no doubt affirm, trying to heat up Olive Oil (or her sisters Sunflower and Flax) more than once is a perilous pursuit.

Terry Robson

Terry Robson

Terry Robson is the Editor-in-Chief of WellBeing and the Editor of EatWell.

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