|What we know:
Polyunsaturated fat is found in greatest amounts in foods from plants, including safflower, sunflower, corn, soybean, and cottonseed oils, and many kinds of nuts. A type of polyunsaturated fat is called omega-3 fatty acids, which are being studied to see if they help guard against heart disease. Good sources of omega-3 fatty acids are some fatty fish, such as salmon, tuna, and mackerel. When used instead of saturated fat, monounsaturated and polyunsaturated fats help lower blood cholesterol levels.