Like carbohydrates and proteins, fats are one of the three main components of the food you eat. The body uses fat as a fuel source, and fat is the major storage form of energy in the body. Fat also has many other important functions in the body. You need some fat in your diet for good health. Too much fat or too much of the wrong type of fat can be unhealthy. Oil and butter contain fat. Nuts, meat, fish, and some dairy products contain fat, too.