We conclude that, in males with obesity, intraduodenal calcium, when administered alone, stimulates GLP-1 and PYY secretion and pyloric pressures and enhances the effects of Trp to stimulate CCK, GLP-1, and PYY secretion, associated with greater suppression of energy intake. The gene discussed is GCG; the disease is obesity due to melanocortin 4 receptor deficiency.