Virgin sunflower oil is very important in the diet because it contains a high percentage of linoleic acid (58%). This fatty acid is said to be essential because humans cannot synthesize it. It must therefore be provided by food. In the body, linoleic acid is converted into a series of longer, more unsaturated fatty acids. These are involved in most physiological functions. They play a structural role within cell membranes and are also the source of biologically active prostaglandins in the regulation of cellular metabolism. Virgin sunflower oil is used in diets aimed at preventing cardiovascular diseases and lowering "bad cholesterol" (accompanied by raw ingredients in salads and raw vegetables). Additionally, sunflower oil is rich in vitamin E, a natural antioxidant.