The Metabolic and Genetic Drivers of Body Composition Changes Following Weight Loss Surgery

Inclusion Criteria (Bariatric Surgery Patients): * Age: 18 to 65 years at time of consent * BMI: 35-65 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. 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 or immunosuppressant use for 8 or more consecutive days in the past 6 months, or any use of anabolic steroids or growth hormones in the same period. * Body mass index \< 35 or \> 65 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.