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 reports. “I was surprised as I’d always thought of sunflower oil as being ‘healthy,'” chemistry professor Martin Grootveld told 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.