The purpose of the trial is to assess the effects of combining regular, generous intakes of high quality protein (primarily from dairy and other animal source proteins) with calorie restriction and low-intensity exercise on muscle quality and muscle adipose infiltration (along with bone mineral density [BMD] and a number of secondary outcomes) in frail, obese, older adults participating in a 6 month intervention. The investigators will compare these effects to those of a traditional control regimen of calorie restriction and low-intensity exercise over the same duration.

Obese older adults (≥60 yrs) with moderate functional impairment will be randomized to 1 of 2 study arms. Outcomes to be measured at 0, 3 and 6 months are as follows: Primary outcomes- (1) Muscle Quality (MQ): muscle power (time to perform ten chair rises, height of the chair, leg length, body mass, and acceleration of gravity) in relation to muscle mass (CT-scan) and (2) Muscle adipose infiltration (MAI) (CT-scan). Secondary outcomes- Bone Mineral Density (BMD; DXA scan) physical function (Short Physical Performance Battery (SPPB); 6 minute walk; 8-foot up and go; and 30 second chair stands; handgrip strength; body weight; fat mass; waist circumference; activity (accelerometers); mental health (sleep, depression, quality of life); and feasibility factors (adherence, protein intake, nutrition adequacy). BMD will only be accessed at 0 and 6 months.

Study Arms:

• Weight loss plus low-intensity exercise intervention (WL-LoEX; n = 35): Subjects follow a calorie-reduction diet for a weight loss of ≥10%, protein~0.8g/g/d. Subjects will also participate in three 30-minute low-intensity exercise sessions weekly. One serving of dairy protein/day will be provided to WL-LoEX participants.
• High protein weight loss plus low-intensity exercise intervention (PRO-WL-LoEX; n = 35): Subjects follow a calorie-reduction diet for a weight loss of ≥10%, with a high proportion of high quality protein at each meal. Intakes of > 30g of protein will be achieved three times a day by subjects in this group, with all or predominantly all from animal sources (high quality) and 60-70% of animal protein from dairy foods that will be provided. Subjects will also participate in three 30-minute low-intensity exercise sessions weekly.

Inclusion Criteria:

• BMI >30;
• SPPB score of ≥4 to <10;
• GFR <45 mL/min

Exclusion Criteria:

• Body weight >495 lbs. (BodPod limits);
• estimated glomerular filtration rates (eGFR) less than 45 mL/min;
• symptomatic cardiac disease;
• receiving chemotherapy;
• hemophilia;
• presence of unstable or symptomatic life-threatening illness;
• neurological disease or disorder causing functional impairments;
• inability to walk,
• dementia;
• prescription weight loss medications;
• use of monamine oxidase inhibitors (MAOIs); or
• primary medical provider advises against participation.