Fats to avoid are called trans-fats, they can be found in processed foods, margarine, soups, fast food, processed frozen foods, commercial baked foods, crisps and crackers, breakfast cereals, cookies, sweets, dressings and dips.
Trans fats increase bad cholesterol and the risk of coronary heart disease. Read the ingredient label and look for shortening, hydrogenated or partially hydrogenated oil. The higher up on the list these ingredients appear, the more trans fat.