Complex carbohydrates include starches and fibers. These carbs are comprised of chains of sugar molecules, making them more complex than simple carbohydrates, which consist of single or double sugar molecules. Common sources of complex carbs are whole grains, legumes, and vegetables. Because they digest slowly, complex carbohydrates provide a steady release of energy and help regulate blood sugar levels. This slow digestion also supports sustained energy for physical activities and can aid in maintaining a healthy weight.