Carbohydrates or sugars are an important energy source to meet the caloric needs of the patient. In meeting the energy needs of humans, the "large" calorie unit or kilocalories, abbreviated as kcals, is used. As a caloric source, there are between 3.4 to 4 kcal per gram of carbohydrate. In adults, the normal caloric requirement is between 25 to 30 kcals per kg of body weight each day. As in the above example of a 70 kg patient, the amount of calories from carbohydrate sources could be in the range of 1750 to 2100 kcals or per day, but often much less, as fat is also an important caloric source. If therapy is provided by a catheter into the stomach or intestine, whole or complex sources of carbohydrates are used, such as from corn syrup, whereas if therapy is provided by an intravenous catheter, the carbohydrate source is in a simplified form as glucose or dextrose sugars.

During acute illness however, many patients will not tolerate even modest amounts of carbohydrates and may develop high blood sugar or glucose levels. High blood glucose levels are associated with an increased risk of infections. To minimize this complication, not only can the amounts of carbohydrate reduced even further, but blood sugar control with aggressive insulin therapy is given. In addition, a portion of the carbohydrate calories may be substituted with fat to further reduce the need the chances of high blood sugars.