Complex carbohydrates often supply energy and other nutrients and fiber that the body needs. They are a better choice. STARCH - in the body breaks down into simple sugars. The body has to break down all sugar/starch into glucose to use it.Complex carbs pack in more nutrients than simple carbs. They're higher in fiber and digest more slowly. This also makes them more filling, which means they're a good option for weight control.Since complex carbs are digested more slowly than simple carbohydrates, most sources do not raise blood sugars as quickly as simple carbohydrates. Whole grains (rather than refined grains), starchy vegetables, non-starchy vegetables, and are the best complex carbohydrates.