A complex carbohydrate is a carbohydrate built from many linked sugar units, principally starches in foods and glycogen in the body, along with dietary fibre. Because digestive enzymes must break these long chains step by step, complex carbohydrates generally release glucose more gradually than simple sugars, giving steadier energy and greater satiety, especially when fibre is present. Whole grains, legumes, potatoes, and vegetables are the main sources. Refining strips away the fibre and micronutrients, leaving rapidly digested starch. Dietary guidance favours complex carbohydrates from whole foods as the foundation of energy intake, typically around half of calories.