The rise of blood glucose in normal and diabetic subjects after meals varies markedly and depends on many factors, including the source of the carbohydrate, its method of preparation, and the composition of the total meal. Classification of carbohydrates as simple or complex does not predict their effects on blood glucose or insulin. Rapidly absorbed carbohydrates, which produce large blood glucose and insulin responses, may be in the form of both sugars and starches. Sugars added to foods have no different effect on blood glucose from those of sugars alone. The natural sugars in fruit and fruit juices raise blood glucose approximately as much as does sucrose and less than do most refined starchy carbohydrate foods. The optimum amount of sugars in the diet is not known. However, undue avoidance of sugars is not necessary for blood glucose control and is not advised because it may result in increased intakes of fat and high-glycemic-index starch.