Chemical Structure. A carbohydrate is a simple sugar. Its basic structure is composed of the elements carbon, hydrogen and oxygen, with generally twice the hydrogen as carbon and oxygen. In its simplest form, a carbohydrate is a chain of sugar molecules called monosaccharides.ou’ll also add a lot of simple carbs to your diet if you eat processed foods and soft drinks. Complex carbs are found in whole-grain foods like breads and cereals. You’ll also find them in starchy vegetables and legumes, like beans. Fiber is an important type of carbohydrate found in plant foods.