POLYUNSATURATED vegetable oils from plants like soybeans and sunflowers are generally praised by nutritionists because they help people keep their cholesterol down and, it is believed, avoid heart disease. But a new study reports that when used to fry foods, the oils produce a toxic compound that has been associated with illnesses, including cardiovascular disease, Parkinson's and Alzheimer's diseases, and liver problems. The findings, the researchers say, highlight the risk of reheating the .