Weight loss surgery is very good at reducing body weight but it can also cause the loss of both muscle and strength. Some patients undergoing weight loss surgery do not achieve their weight loss goals and regain the weight they lost. When this occurs, the loss of muscle and strength combined with the regain of weight can impact the individual's quality of life and ability to remain active and mobile.

The purpose of this study is to understand the behavioral, biological, and genetic factors that influence the success of weight loss surgery and its impact on muscle mass.

Bariatric surgery patients participating in the trial will be monitored prior to, and for a year following weight loss surgery, with data collected about their eating habits, hand grip strength, and the loss of fat, muscle, and body weight following surgery. In patients who undergo a routine endoscopy in advance of weight loss surgery a small sample of gut tissue will be collected to identify the expression (activity) of genes in their DNA.

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.

Patients will be recruited from those electing to undergo bariatric surgery at the University of Texas Medical Branch.

Given the small participant numbers involved, the sharing of individual participant data could carry the risk of re-identification of the study participants, despite the data being provided in de-identified form.