Glycogen storage disease type I (GSD I) caused by deficiency of glucose-6-phosphatase enzyme leading to buildup of a complex sugar called glycogen in liver and low blood glucose level. Nutritional treatment involves supplying carbohydrates and uncooked cornstarch. Glycosade® (modified cornstarch) has shown promise in maintaining normal blood glucose level in GSD I. But the difficulty in nutritional treatment is determining the best type of carbohydrate to be given to avoid low blood glucose. Thus, there is a need to develop a simple test to examine glucose digestion and measure the utilization of different carbohydrates in GSD I and healthy controls.