In order to match peripheral glucagon concentrations between study visits, a small dose of glucagon will likely need to be administered intravenously at 9am, during the placebo arm of the study. Based on the pharmacokinetics of glucagon, we are likely to administer 0.00625mg-0.025mg, although further dose titration may be necessary (maximum dose 0.1mg). Free fatty acids, triglycerides, insulin, glucagon, C-peptide, glucagon-like peptide-1 (GLP-1) and GIP,as well as glucose isotopic enrichment will be measured.