Complex carbohydrates are chains of three or more single sugar molecules linked together. Long chains of sugar molecules called starches serve as a storage form of energy in plants and when you eat those plants, your body breaks down the carbohydrates for your own energy needs. Another form of complex carbohydrate called cellulose forms the structural components that give plants their shape, and is a main component of dietary fiber.
Foods with large amounts of complex carbohydrates include legumes, starchy vegetables like potatoes and corn, rice and grain products. Other vegetables such as green beans, broccoli and spinach contain less starch, but they have more fiber.
Complex carbohydrates should supply about half the calories in your diet; however, the best complex carbohydrates come from legumes, vegetables, breads, pasta and cereals. Choose 100% whole wheat or 100% whole grain brad cereal and pasta products over refined flour products because they contain more fiber. The extra fiber slows down the absorption of the carbohydrates so you feel full longer and be less likely to over-eat throughout the day.