When you eat complex carbohydrates, they get converted to glycogen and either used immediately for energy, providing a steady dose of blood sugar, or they are stored in the muscles and liver for energy at a later time.
Whole grains are high in fiber, have moderate protein levels, are low in fat and are also a good source of complex carbs. Specific examples include millet, oats, wheat germ, barley, wild rice, brown rice, buckwheat, oat bran, cornmeal and amaranth. Any product that is made from these grains is also complex as well. Whole grain bread, bagels, buns and rolls are examples of these. Also pasta, macaroni and breakfast cereals that are made from whole grains are complex carbohydrates.
Fruits are high in water content, fiber, vitamins and they have virtually no fat at all. Fruits packed with complex carbohydrates include apricots, oranges, plums, pears, grapefruits and prunes.
Vegetables are high in water, low in fat, have multiple vitamins and minerals, and most varieties are complex carbs. Broccoli, cauliflower, spinach, turnip greens, eggplant, potatoes, yams, corn, carrots, onions, all types of lettuce, celery, cucumbers, cabbage, artichokes and asparagus are all examples of these.
Legumes are oftentimes called pulses. These are characterized by seeds that have an exterior pod surrounding them. Beans are a type of legume that is a complex carbohydrate. Specific examples include lentils, kidney beans, black beans, peas, garbanzo beans, soy beans and pinto beans.
Soy milk made from soy beans is a complex carb and dairy products like low-fat yogurt and skim milk are also complex carbs.
From article by Kevin Rail - livestrong.com