You may be familiar with trans fats but may not know much about hydrogenated oils, which can be a source of trans fat. Hydrogenation is a process that turns vegetable oil into a more solid form, which makes it a more shelf-stable product. There are two types of hydrogenated oils: partially hydrogenated and fully hydrogenated.

A partially hydrogenated oil is made by heating a polyunsaturated fat, such as soy, corn or cottonseed, with hydrogen and a catalyst. This process breaks the double bonds in the fat, creating a combination of monounsaturated and saturated fats. Partially hydrogenated oils are semisolid fats at room temperature. These types of fats are the source of trans fats in the diet, and are considered unhealthy fats because of their effect on heart health.

Fully hydrogenated fats are solid fats at room temperature. Like partially hydrogenated fats, fully hydrogenated fats are created by breaking the double bonds in the polyunsaturated fats. However, all of the bonds in the liquid fats are broken, creating a fat that contains only saturated fat. Fully hydrogenated fats are considered healthier than partially hydrogenated fats, because they're not a source of trans fats.

Hydrogenated oils are used to replace other hard fats, such as butter, lard or coconut oil, in processed foods. In addition to improving shelf life, hydrogenated oils also mimic the taste and mouth feel of the other types of hard fats. Even though there's concern about the trans fats found in hydrogenated oils, they're considered safe ingredients by the U.S. Food and Drug Administration.

Palm kernel oil is a vegetable oil that is high in saturated fat and more solid than vegetable oil. Some food manufacturers use a hydrogenated version of palm kernel oil, which helps to give the necessary properties for the food it's used in, with less trans fat. You can find palm kernel oil in chocolate and coffee creamer.