Not all trans fats are bad fats. Generally, bad fats are manufactured trans fats. They are also known as hydrogenated or partially hydrogenated vegetable oil. Manufactured trans fat is a heavily processed vegetable oil. All hydrogenated and partially hydrogenated oils are trans fats. Partially hydrogenated vegetable oil is one of the top ingredients in most packaged foods: cookies, snack chips, pretzels, most peanut butter, and shortening. Many fast food chains fry their foods in partially hydrogenated oils.
Natural trans fats are found in dairy products and certain other foods. They have not shown to be harmful.
Vegetable shortening and most margarines contain trans fats. Trans fats begin as natural, polyunsaturated fats that are then exposed to chemical processes that change the molecular structure by artificially saturating the fat with hydrogen in the manufacturing process. Manufactured trans fats are synthetic saturated fats.
Manufactured trans fat raises LDL (bad) cholesterol levels and lowers HDL (good) cholesterol levels. It raises levels of triglycerides, another form of lipid, which can increase the risk of heart disease.
Commercial baked goods such as crackers, cookies, cakes, and many fried foods like doughnuts and French fries may contain trans fats. Shortening and margarine may also be high in trans fats. In the United States, if a food has less than .5 grams of trans fat per serving, the food label can read 0 grams trans fat.
According to the Mayo Clinic, in a healthy diet, 25 to 35 percent of your total daily calories can come from fat, but saturated fat should account for less than 10 percent of your total daily calories.
Monounsaturated fat, found in olive, peanut, and canola oils is a healthier option than saturated fat. Nuts, fish, and other foods containing unsaturated omega-3 fatty acids are also good choices of foods with monounsaturated fats. Consumption of bad trans fats has gone down in recent years and decades.