Long gone are the days when all fats were "bad." Now we know that what’s important are the types of fat we eat, and how much. For instance, oils—full of unsaturated fatty acids—generally fall into the "healthy" camp. When you choose oil over a solid fat, such as shortening or butter, you’re helping to cut back your consumption of saturated fats, one of the nutritional bad guys. Similarly, when you choose nuts over crackers you may be limiting your intake of trans fats, another type of unhealthy fats.
Fats 101: All food sources that we think of as "fats"—we’re talking butter, shortening, oils—are made up of a combination of fatty acids: monounsaturated, polyunsaturated and saturated. All fats contain all three types but are classified by the type of fatty acid that makes up most of the fat. For example, olive oil is about 78 percent monounsaturated fat, so it’s considered a monounsaturated fat. Trans fats are man-made fats used in processed foods to increase their shelf life.