The purpose of this study is to determine the effect of meal size and texture on the levels of incretin hormone, GLP-1, after Gastric Bypass Surgery (GBP). Patterns of food intake change after bariatric surgery and patients often eat multiple small low-calorie meals, a pattern that may affect blood glucose as well as incretin levels. Whether the release of GLP-1 after an oral challenge or a single liquid meal has any physiological relevance in 'real life' setting of multiple small meals diet is unclear.