<qa>  What is the primary outcome of the test?There are 2 primary outcomes: 1 Change in plasma GIP response to glucose after GBS and 2 change in insulin sensitivity after GBS, as measured by an area-under-the-curve equation for a standardized 180-minute oral glucose tolerance test. Secondary outcomes include 1 Change in plasma GLP-1 response to glucose after GBS and 2 change in plasma glucagon response to glucose after GBS, as measured by the equation used for the primary outcome. 