Simple carbohydrates are sugars. Simple carbohydrates can be naturally occurring or added to foods. Natural sugars are found in fruit, dairy, vegetables and other whole foods. Fructose, for example, is a simple carbohydrate sugar in fruit. Added sugars, such as sucrose and dextrose, are packed into processed foods. These are normally low in nutrients and high in calories. During digestion, enzymes in your small intestine rapidly metabolize sugar into glucose and send it into your bloodstream where it’s used for energy. Complex carbohydrates are starches from potatoes, peas, corn, whole-grains and many other foods. Starches undergo numerous stages of conversion in your digestive tract before they convert to glucose. Because of different transit times in your gut, sugars give you a quick burst of energy, while starches provide more of a sustained energy level.