For the hyperglycemic clamp study, a catheter (thin flexible tube) is inserted into a vein in each arm. A sugar solution is given through one tube and blood samples are drawn every 5 minutes through the other to measure insulin. For the food intake testing, the child is asked about his or her hunger level, then given various foods he or she may choose to eat, then questioned again at various intervals both during and after finishing eating about his or her hunger level. The doubly labeled water study involves drinking "heavy water" (water which is enriched to have special kinds of hydrogen and oxygen). Urine specimens are collected 2, 3 and 4 hours after drinking the water. The child also drinks a special milk shake called a Scandishake and repeats the calorie intake and hunger study. (Two food intake studies are done on separate days.) One week after the heavy water test, additional urine samples are collected one week later.