Carbohydrates are the major source of energy for humans. Following their digestion, almost all ingested carbohydrates are converted to glucose. Glucose is the primary oxidative fuel for the brain. Although few studies have been done in infants and children to de®ne the upper and lower limits of carbohydrate intake, such information may be derived from the published data on glucose metabolism in vivo. The upper and lower limits are determined by the need to provide for total energy expenditure, need for other essential nutrients such as protein and fats, requirements of the glucose dependent tissues such as the brain, and the need to minimize the protein cost of gluconeogenesis and thus irreversible loss of nitrogen. With these considerations, the upper and lower boundaries of carbohydrate intake in relation to age are described.