Children with growth hormone deficiency (GHD) have increased insulin sensitivity and may present with hypoglycemia during infancy. Treatment with recombinant human growth hormone (rhGH) reduces the risk for hypoglycemia and decreases insulin sensitivity. The investigators hypothesize, that GHD causes a decrease in the fraction of glucose derived form gluconeogenesis and conversely glycogenolysis and insulin sensitivity will be increased, when GHD children are compared to healthy controls. The investigators anticipate that total glucose production will be unaffected by rhGH therapy. Therefore, the GDH subjects treated with rhGH for 8 weeks will have an increase in the fraction of glucose derived form gluconeogenesis and a decrease in that form glycogenolysis and decreased insulin sensitivity. To test this hypothesis, 10 healthy and 10 GHD children will be studied using the stable isotope \[U-13C\] glucose and Mass Isotopes Distribution Analysis (MIDA). The investigators will be specifically measuring the rate of glucose production, gluconeogenesis, glycogenolysis, insulin sensitivity and glucagon response after an overnight fast. In addition, the investigators will measure changes in protein oxidation, proteolysis and fat metabolism using the stable isotopes \[15N2\] urea, \[1-13C\] leucine and concentrations of free fatty acids and b-hydroxybutyrate. The GHD group will be studied at the time of diagnosis and after 8 weeks of rhGH.
