The second baseline testing session (BV2) will occur in the Wake Forest University Department of Health and Exercise Science. During this visit, participants will undergo muscle function tests (expanded Short Physical Performance Battery (SPPB) test, Timed-Up-and-Go (TUG) test, fast 20-meter and 400-meter walk tests, and stair climb test), DXA scan (whole body, hip and spine), physical activity questionnaire (Community Healthy Activities Model Program for Seniors; CHAMPS), quality of life questionnaire (SF-12), disability questionnaires (Pepper Assessment Tool for Disability; PAT-D and Mobility Assessment Tool-short form; MAT-sf), and instructions will be provided for a dietary run-in (approximately 30 minutes). For the dietary run-in, all participants will be provided with and oriented to the Medifast® QuickStart Guide, sample meal plans, 3, one-day dietary trackers, a sampling of 12 Medifast Meal Replacement Products, 3, one-day Product Evaluation Forms, and asked to follow the Medifast 4 & 2 & 1 PlanTM for a three day period occurring over the following week. Participants will be contacted by the study registered dietitian (RD) upon completion of the dietary run in period to assess their willingness and self-efficacy to adhere to the dietary protocol for the duration of the study (24 weeks). Participants who indicate that they are willing and able to follow the protocol will be randomized (RAND) to one of the 2 study interventions (high protein weight loss group vs. weight stable control group), with blocking stratified by gender, and treated in 5 successive waves (n=12-13 participants/group/wave). Randomization of the entire wave (n=24-26) will occur approximately 1week prior to the start of intervention, and at this time the first monthly Medifast product order will be placed for participants randomized to the high protein weight loss group.