For this study, investigators will measure fasting and postprandial (happening after a meal) gut hormones, bile acid, amino acids, vitamin B, vitamin D, myokines and adipokine levels in obese individuals who are at least 2 years after a Roux-en-Y gastric bypass (RYGB). Investigators will also measure resting metabolic rate (RMR) (the amount of energy expended daily) and body composition (the proportion of fat, muscle, and bone of an individual's body). The subjects body composition will be analyzed, including fat mass and fat free mass, by a Dual-Energy X-ray Absorptiometry (DEXA). This study will provide more information regarding the effect of RYGB on gut hormones, adipokines, bile acids, amino acids, and energy expenditure and body compositions.