GIP and type 2 diabetes mellitus: Initially discovered in 1973 for its role in inhibiting gastric acid secretion in excised canine stomach pouches, and later shown to not have this effect in humans (Meier et al., 2004a), GIP promotes nutrient-stimulated insulin secretion and increases glucagon secretion in the fasted state but not in patients with type 2 diabetes (Baggio and Drucker, 2007; Christensen et al., 2011).