Summary : Carbohydrates are an important energy source, fueling the central nervous system and muscles during physical activity. Supplying four calories per gram, carbohydrates also help the body efficiently use vitamins, minerals, amino acids and other essential nutrients. Scientists classify carbohydrates into two categories: simple and complex carbohydrates because they consist of one or two sugars units. Sugars occur naturally in fruits, vegetables, milk and other foods, as well as in a refined state, such as table sugar or sucrose. The body cannot distinguish between naturally-occurring and added sugars and digests both in exactly the same manner. Complex carbohydrates, found in grain foods, fruits and vegetables, get their name from their complex chain-like structure of many sugars units. Included in this category are starches and dietary fiber. During digestion, starch is typically broken down into sugars and used by the body for energy. Studies indicate that high-fiber diets can reduce the risks of heart disease and certain types of cancer. Soluble fiber in cereals, oatmeal, beans and other foods has been found to lower blood cholesterol. Insoluble fiber in cauliflower, cabbage and other vegetables and fruits helps move foods through the stomach and intestine, thereby decreasing the risk of cancers of the colon and rectum.