What we now know:
Saturated fats, cholesterol, and trans fatty acids are unhealthy and are associated with an increase in cardiac events and should be avoided. They are found with fatty meat, with the skin of poultry, in whole or higher fat dairy products such as butter, cream, milk, or cheese, and hard vegetable oils such as stick margarine or partially hydrogenated products.
Good fats include mono-unsaturated fats and poly-unsaturated fats and are essential for health. Mono-unsaturated fats are found in products made from olive oil, canola oil, peanut oil, nuts, and seeds. Poly-unsaturated fats include omega-3 and omega-6 fatty acids. Omega-3 fatty acids are found in most fish as well as canola oil, flaxseeds, flaxseed oil, and nuts such as walnuts. Omega-6 fatty acids are found in canola oil, corn oil, safflower oil, as well as cottonseed oil. Products made with these oils include soft or squeeze margarine products, mayonnaise, and salad dressings.
Good fats (usually referred to as healthy oils) are rich in anti-oxidants, oil-based vitamins, and are associated with reduced cardiovascular events. Mono-unsaturated fats increase the HDL or healthy cholesterol, while a good balance of products rich in both omega-3 and omega-6 fatty acids provide some anti-clotting benefits and appear to reduce the likelihood of cardiac arrhythmias as well as second heart attacks. Certain plant oils called plant sterols and stanols reduce LDL cholesterol and can be used as a supplement or added to spreads to actually improve cholesterol levels.