Carbohydrates are substances that are found in foods such as bread and pasta, which provide the body with heat and energy. Chemically, carbohydrates are made of three kinds of elements namely carbon , hydrogen and oxygen.Carbohydrates are separated into two main categories, simple carbohydrates and complex carbohydrates. Simple carbohydrates are those that contain one or two sugar molecules linked together. Complex carbohydrates are those that contain three or more sugar molecules linked together. In some cases these chains can contain hundreds of sugar molecules.