University of Texas Medical Branch

(Healthy Volunteers): - Age: 30 to 50 years at time of consent - BMI: 20-25 kg.m-2 - Male or Female - All races and ethnic backgrounds - Ability to speak and read English - Subject has provided informed consent in a manner approved by the IRB and is willing and able to comply with the trial procedures. Inclusion Criteria (Bariatric Surgery Patients): - Age: 18 to 65 years at time of consent - BMI: 35-50 kg.m-2 - Scheduled to undergo bariatric surgery at UTMB - All races and ethnic backgrounds - Ability to speak and read English - Subject has provided informed consent in a manner approved by the IRB and is willing and able to comply with the trial procedures. Additional inclusion criteria for patients undergoing enhanced metabolic assessment: - Age: restricted to 30 to 50 years of age - Undergoing gastric bypass surgery

(Healthy Volunteers): - Heart, vascular, or pulmonary disease - Uncontrolled blood pressure (systolic BP > 170, diastolic BP > 95 mmHg) - Impaired renal function (creatinine > 1.5 mg/dl) - Anemia (hematocrit < 33 % or donated blood in the past 12 weeks.) - Diabetes mellitus or other untreated endocrine or metabolic disorder - Recent (5 years or less) history of cancer - Systemic steroids, anabolic steroids, growth hormone, or immunosuppressant use within 6 months. - Recent (6 months) adherence to a weight-loss or weight-gain diet, resulting in a weight change of 10% or more. - Body mass index > 25.5 kg.m-2 - Body mass index < 19.5 kg.m-2 or recent history (< 12 months) of disordered eating. - Acute infectious disease or chronic infection. - Pregnancy or breast-feeding. - Recent (1 month) consumption of protein-based sports supplements. - Any medical condition that, in the opinion of the investigator, would place the subject at increased risk for participation. - Known allergic reaction to any agent under investigation or required by the protocol, including Phenylketonuria. - Unable to lie still in a supine position for 10 minutes. - History of prior non-compliance or the presence or history of a psychiatric condition (including drug or alcohol addiction) that would, in the opinion of the investigator, make it difficult for the subject to comply with the study procedures or follow the investigators instructions. - Concurrent participation in another research study. - Use of an investigational agent in the 30 days prior to signing informed consent. Exclusion Criteria (Bariatric Surgery Patients): - Fails the medical criteria for bariatric surgery. - Anemia (hematocrit < 33 % or donated blood in the past 12 weeks.) - Recent (5 years or less) history of cancer - Systemic steroids, anabolic steroids, growth hormone, or immunosuppressant use within 6 months. - Body mass index < 35 or > 50 kg.m-2. - Acute infectious disease or chronic infection. - Pregnancy or breast-feeding. - Any medical condition that, in the opinion of the investigator, would place the subject at increased risk for participation. - History of prior non-compliance that would, in the opinion of the investigator, make it difficult for the subject to comply with the study procedures or follow the investigator's instructions. - Concurrent participation in another research study. - Use of an investigational agent in the 30 days prior to signing informed consent. Additional exclusion criteria for patients undergoing enhanced metabolic assessment: - Known allergic reaction to any agent under investigation or required by the protocol, including Phenylketonuria. - Unable to lie still in a supine position for 10 minutes. - Previous bariatric surgery or undergoing a procedure other than gastric bypass (e.g. sleeve gastrectomy).