evidence: The term "vegetable oil" is used to refer to any oil that comes from plant sources, and the healthfulness of a vegetable oil depends on its source and what it’s used for. Most vegetable oils on the market are a blend of canola, corn, soybean, safflower, palm and sunflower oils. "Generally I tell people to use olive oil whenever you can instead of a corn or a soybean oil," says Weinandy. They’re not necessarily bad for you, she says, "but you can get so much more benefit from olive oil." Still, vegetable oils are refined and processed, which means they not only lack flavor, but also nutrients, Howard says. "Vegetable oil is guaranteed to be highly processed. It’s called ‘vegetable’ so that the manufacturers can substitute whatever commodity oil they want—soy, corn, cottonseed, canola—without having to print a new label," she says. "Processed oils have been pushed past their heat tolerance and have become rancid in the processing." Some of these oils, especially palm, are associated with more degradation of land for production, Howard says.