Experiments at De Monfort University, recently published by the Daily Telegraph have shown that corn and sunflower oil used in frying can release dangerously high levels of toxic chemicals known as valdehydes, which have been linked to cancer, and heart disease and dementia. Experiment leader Dr Martin Grootveld, a professor of bioanalytical chemistry and chemical pathology at the University has stated that “a typical meal of fish and chips” fried in these vegetable oils contained up to 200 times more aldehydes than are considered safe. Olive oil, butter, and coconut oil, on the other hand, contained far lower levels of aldehydes.
During his appearance on BBC’sTrust Me, I’m a Doctor, Dr. Grootveld gave volunteers sunflower oil, vegetable oil, corn oil, cold-pressed grapeseed oil, olive oil, butter, goose fat, and lard, and asked the participants to cook foods with them every day. Leftover oil from their cooking was collected and sent to the lab at De Montfort University where they found that sunflower oil and corn oil produced aldehydes at the highest levels, and that it was actually safer to use olive oil, butter, lard, or coconut oil.
"People have been telling us how healthy polyunsaturates are in corn oil and sunflower oil. But when you start… subjecting them to high amounts of energy in the frying pan or the oven, they undergo a complex series of chemical reactions, which results in the accumulation of large amounts of toxic compounds.” Dr Grootveld commented.
“Sunflower and corn oil are fine as long as you don’t subject them to heat, such as frying or cooking,” Grootveld said in a press release. “It’s a simple chemical fact that something which is thought to be healthy for us is converted into something that is very unhealthy at standard frying temperatures.” Olive oil, meanwhile, is much better “because lower levels of these toxic compounds are generated, and secondly, the compounds which are formed are less threatening to the human body.
For years we have been subjected to official health advice not to use butter or lard for cooking. These experiments however show that both are very good for frying purposes. I myself will stick to light olive oil for cooking, and a stronger flavoured virgin olive oil for use in salads.
The following article in Stuff.co.nz expands on the issues and is well worth reading.