Additional Study Information: We are conducting a research study on how insulin controls the livers production of glucose (sugar) and fat in people at risk for type 2 diabetes. We are seeking adult volunteers, aged 18-65, who are overweight or obese with a body mass index of 27-50 and have been diagnosed with, or are at risk for, prediabetes. Participants will undergo two pancreatic clamp procedures separated by 2-8 weeks. A pancreatic clamp is a technique in which we temporarily shut off the body's production of insulin with intravenous (into the vein) hormone mixtures that allow researchers to vary levels of the blood sugar-lowering hormone, insulin, over about 6 1/2 hours. The goal is to see how lowering the insulin level affects sugar and fat production by the liver. Participants will be required to stay overnight before the clamp; receive intravenous (in the vein) infusions of sugar and fat tracer molecules (not radioactive!); have blood samples drawn to measure the levels of sugar, fats, and other molecules; and follow a special diet. Participants will attend two outpatient screening visits, two inpatient visits of up to 30 hours, and will be compensated up to a total stipend (salary) of $1000 plus additional reimbursement for travel expenses.