Additional Study Information: We are conducting a research study on how insulin controls blood sugar in both healthy people and those at risk of type 2 diabetes. We are seeking adult volunteers, aged 18-65, who have body mass indices either in the lean range (18-25 kg/m2) or in the obesity range (30-45 kg/m2) but who do not have prediabetes or diabetes. Participants will undergo a graded insulin suppression test (GIST) procedure in which we temporarily shut off the body's production of the blood sugar-lowering hormone insulin with an intravenous (into the vein) medication so that we can vary insulin levels over about 5 hours. The goal is to see how different doses of insulin affects blood sugar. Participants will attend a screening visit and, if eligible for participation, a study visit of up to 7-8 hours. At both visits, blood samples will be drawn to measure the levels of sugar, fats, and other molecules. Those completing the study will be compensated with a stipend (salary) of $350, plus additional reimbursement for certain travel expenses.