Like cooking with vegetable oils as a "healthy" alternative to lard and butter? A professor in England has some bad news: When you heat up oils such as sunflower or corn oil, they produce intense concentrations of chemicals known as aldehydes that have been associated with dementia, heart disease, and cancer, the Telegraph reports. "I was surprised as I'd always thought of sunflower oil as being 'healthy,'" chemistry professor Martin Grootveld told the BBC in July. In his study, Grootveld had people cook with various oils and fats and hand over the remainder for analysis at De Montfort University in Leicester, England; his team also heated the same fats and oils and compared the findings. They found that molecular structures in these products changed at around 356 Fahrenheit, causing them to oxidize and produce lipid peroxides and aldehydes.
Vegetable oils were the worst offenders, while lard, olive oil, and butter produced far fewer aldehydes, and coconut oil the least of all. (But vegetable oils are "fine" when not fried or cooked, Grootveld says.) John Stein, emeritus professor of neuroscience at Oxford, says vegetable oils are among the factors damaging our brains (with mental health problems and dyslexia, for example) by replacing necessary omega-3 fatty acids with omega-6 acids. "The human brain is changing in a way that is as serious as climate change threatens to be," Stein says. All of this may undermine the notion that vegetable oils are healthier than animal products that are rich in saturated fats. (Read about an "intriguing new twist" in the omega-3 story.)