Surgical vs. Lifestyle in Obese Older Adults

Inclusion Criteria: * Patients must be aged 55-75 at the time of recruitment, * speak English, * meet medical eligibility criteria for WLS (i.e. BMI of \>40 or \>35 with a major obesity comorbidity), * and be willing and able to participate in study procedures including the physical activity intervention and complete follow-up. Exclusion Criteria: The investigators will exclude participants for whom * intentional weight loss might be inappropriate (e.g. patients with serious life-limiting illness) * or who might be psychologically unstable (e.g. moderate to severe depression on the PHQ-9) * or who have contraindications to a high protein diet or the physical activity intervention (e.g. recent MI/CVA in last 6 months, uncontrolled congestive heart failure, serum creatinine \> 2.0 mg/dl/on dialysis, h/o celiac disease/crohn's disease/ulcerative colitis.) * or patients whose weight exceeds 450 lbs (weight limit of DXA). * The investigators will withdraw bariatric subjects who do not undergo weight loss surgery and his or her matched lifestyle subject. The investigators will withdraw subjects in the lifestyle group who do not attend at least attend two of the first three nutrition and physical therapy visits. The investigators will recruit additional subjects to replace lifestyle subjects who are withdrawn from the study for this reason.