Choosing a low-fat dressing for your salad might help with keeping the calories down but a recent study suggests that you could be missing out on other health benefits. The study, undertaken by Iowa State University, involved feeding 29 people salads dressed with butter, high in saturated fat, canola oil for monounsaturated fat, and corn oil for polyunsaturated fat. Each salad had 3g, 8g or 20g of fat.