Changes in Gut Hormones, Body Composition and Energy Expenditure After Roux-en-Y

The purpose of this study is to gain a better understanding of the mechanism of weight regain through gut hormone (substances in the gut that control various functions of the digestive organs) and energy expenditure (the amount of energy a person uses to complete bodily activities). Our hypothesis is that gut hormone response might be different among subjects who are able to maintain weight loss and subjects with weight regain. 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.