51Âþ»­

Frying with vegetable oils may not be as healthy as many people think, according to research carried out at by experts at 51Âþ»­ Leicester (51Âþ»­).

The BBC asked 51Âþ»­’s Professor Martin Grootveld, professor of bio-analytical chemistry and chemical pathology, to help investigate the “healthiest” oils to cook with for its series Trust Me I’m A Doctor, shown on BBC 2 on Wednesday 29 July.

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PRESENTER: Michael Mosley of BBC's Trust Me, I'm a Doctor

Volunteers were given sunflower oil, vegetable oil, corn oil, cold-pressed rapeseed oil, olive oil, butter, goose fat and lard and asked to use them in every day cooking. They collected any leftover oil and sent it to 51Âþ»­’s labs to be analysed.

When fats and oils are heated the molecular structure changes, producing chemicals called aldehydes that may cause heart disease and cancer.

Professor Grootveld’s team found sunflower oil and corn oil produced aldehydes at levels 20 times higher than recommended by the World Health Organisation. Olive oil and rapeseed oil produced far fewer aldehydes as did butter and goose fat.

Not only that, but Professor Grootveld's team also identified two previously unknown aldehydes in the samples of these oils - a world first.

He said: “Sunflower and corn oil are fine as long as you don't subject them to heat, such as frying or cooking. 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."

He recommends olive oil for frying or cooking: “Firstly, because lower levels of these toxic compounds are generated, and secondly the compounds which are formed are less threatening to the human body.”

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EXPERIMENTS: Professor Grootveld, who has carried out research in this area for several years

Presenter Michael Mosley said: “Put simply, cooking with these oils is producing even more toxic compounds than has ever before been realised. In contrast, the olive oil and cold-pressed rapeseed oil produced far fewer aldehydes, as did butter and goose fat. The reason being that these fats are richer in mono unsaturated and saturated fats, and are much more stable when heated.

“I was surprised as I'd always thought of sunflower oil as being 'healthy'."

Professor Grootveld has been carrying out research in this area for many years and is a respected consultant for a wide variety of healthcare, pharmacy and food companies.