6. GI peptides measurements: The plasma designated for GLP-1 measurement will be supplemented with aprotinin (1,000 kallikrein inactivation unit (KIU)/ml) and dipeptidyl peptidase-4 inhibitor (20 μl/ml plasma; Millipore, St. Charles, MO). Plasma insulin, c-peptide, glucagon, GIP, active GLP-1 (7-37 and 7-36 amide), peptide YY, pancreatic polypeptide, and leptin were measured by multiplex immunoassays (Luminex, Millipore).