Background: Gastrointestinal complications in diabetes may affect glucose and endocrine homeostasis. Glucosedependent insulinotropic peptide (GIP), glucagon-like peptide- 1 (GLP-1), and leptin regulate glucose homeostasis, food intake, and gastric emptying. Aim: The aim was to investigate associations between diabetes complications and glucose homeostasis and plasma levels of GIP, GLP-1, and leptin. Methods: Sixteen diabetes patients (seven men) were examined with gastric emptying scintigraphy and 72-h continuous subcutaneous glucose monitoring, 14 with the deep-breathing test, and 12 with esophageal manometry. A fiber-rich breakfast was given during the second day of glucose registration. Blood samples were taken 10 min and right before a fat-rich breakfast, as well as 10, 20, 30, 45, 60, 90, 120, 150, and 180 min afterwards. 20 healthy volunteers acted as controls. Plasma was analyzed regarding GIP, GLP- 1, and leptin by Luminex. Results: Gastroparesis lowered maximal concentration (c-max) (p = 0.003) and total area under the curve (tAUC) (p = 0.019) of glucose levels as well as d-min (p = 0.043) of leptin levels. It tended to lower baseline (p = 0.073), c-max (p = 0.066), change from baseline (dmax) (p = 0.073), and tAUC (p = 0.093) of GLP-1 concentrations. Esophageal dysmotility tended to lower tAUC of glucose levels (p = 0.063), and c-min (p = 0.065) and tAUC (p = 0.063) of leptin levels. Diabetes patients had a higher baseline concentration of glucose (p = 0.013), GIP (p = 0.023), and leptin (p = 0.019) compared with healthy subjects. Conclusion: Gastric and esophageal dysmotility are associated with both lesser increases in postprandial glucose elevations and decreased postprandial changes in GLP-1 and leptin.