Vegetable oils such as corn, sunflower, palm and soy produced toxic chemicals when heated. However, coconut oil produced the lowest levels of the toxic chemical.

‘For years, experts suggested using oils high in polyunsaturated fats are better for health than saturated animal fats. But heating the vegetable oils releases aldehydes, which have been linked to heart disease, dementia and cancer.
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Martin Grootveld from DeMontfort University, said, “A meal fried in vegetable oil such as fish and chips contains 100 to 200 times more aldehydes than the daily limit set by the World Health Organization (WHO).”




Cooking using lard, butter and olive oil was found to produce much lower levels of aldehydes - with coconut oil coming out as healthiest.
John Stein, emeritus professor of neuroscience at Oxford University, said "If you eat too much corn oil or sunflower oil, the brain is absorbing too much omega 6, and that effectively forces out omega 3.”
Source-Medindia