The purpose of the study is to determine how blood sugar levels in individuals with and without hypoglycemia after bariatric surgery respond to different doses of glucagon, a hormone that is usually present in your body that regulates blood sugar levels. In this study, there will be 4 visits to the clinical research center. In the first visit, medical history and physical exam will be performed, and blood samples will be taken to assess overall health. During visit 2, a continuous glucose monitor will be placed under the skin. (This may be combined with visit 1, depending on the schedule of visits.) In visit 3, we will test the effect of a total of 4 different doses of glucagon, in increasing doses. In visit 4, we will test the effect of a total of 3 doses of glucagon, in decreasing doses. For both visit 3 and 4, we will infuse labeled stable glucose to allow us to measure how much glucose the body is making, and will measure levels of hormones which regulate glucose, such as insulin and glucagon.