Carbohydrates are made up of sugar molecules linked together to form starches and fiber. They serve four primary functions in the body: providing energy, storing energy as glycogen in the liver and muscles, building macromolecules, and sparing protein and fat for other uses. There are three main types of carbohydrates: monosaccharides like glucose and fructose, disaccharides like sucrose and lactose, and complex carbohydrates. Sources of carbohydrates include fruits containing fructose, dairy products containing galactose and lactose, and cereals, potatoes, and pasta containing maltose.