Utilizing Protein During Weight Loss to Impact Physical Function

The study will use a 3-group design in 225 obese (BMI 27-45 kg/m2), older (65-85 years) men and women at risk for disability (eSPPB <2.5) who will undergo a 6-month weight loss intervention followed by a 12-month follow-up phase to test the overall hypothesis that a higher protein (1.2 g/kg body wt/d) / lower carbohydrate (CHO) diet during a 6-month weight loss intervention improves physical function compared with an isocaloric lower protein (the current Recommended Dietary Allowance (RDA), 0.8 g/kg body wt/d) / higher CHO diet, and whether continuing a higher protein / lower CHO diet for 12-months following weight loss will result in better maintenance of improved physical function. All participants will undergo a 6-month weight loss intervention involving caloric restriction and supervised exercise followed by 12 months of follow-up with randomization to one of three groups (n=75/group): 1) Lower protein / higher CHO diet for the 6-month weight loss phase only (RecProt); 2) Higher protein / lower CHO diet for the 6-month weight loss phase only (6-mo HiProt); or 3) Higher protein / lower CHO diet for the 6-month weight loss and 12-month follow-up phases (18-mo HiProt). Physical function (primary aim) will be assessed by the expanded Short Physical Performance Battery (primary outcome) and lower extremity muscle strength at baseline, 6-, 12- and 18-months. Weight loss maintenance and body composition (secondary aim) will be assessed by dual-energy X-ray absorptiometry (DXA) and computed tomography (CT) at baseline, 6- and 18-months. Bone mineral density (DXA) and cardiometabolic risk factors will also be measured at baseline, 6- and 18-months.

Inclusion criteria

• 65-85 years
• BMI: 27-45 kg/m2
• No regular resistance training and/or aerobic exercise (>20 mins/d) for past 6 months
• eSPPB <2.5
• No contraindications for safe and optimal participation in exercise training
• Approved for participation by Medical Director (Dr. Lyles)
• Willing to provide informed consent
• Agree to all study procedures and assessments
• Willing to consume protein/CHO supplements for up to 18 months
• Able to provide own transportation to study visits and intervention sessions

Exclusion criteria

• Weight loss (≥5%) in past 6 months
• Dependent on cane or walker
• Cognitive impairment (MoCA score <22)
• Severe arthritis, or other musculoskeletal disorder
• Joint replacement or other orthopedic surgery in past 6 months
• Uncontrolled resting hypertension (>160/90 mmHg);
• Insulin-dependent or uncontrolled diabetes (HbA1c ≥8%)
• Current or recent past (within 1 year) severe symptomatic heart disease, uncontrolled angina, stroke, chronic respiratory disease requiring oxygen; uncontrolled endocrine/metabolic disease; neurological or hematological disease; cancer requiring treatment in past year, except non-melanoma skin cancers; liver or renal disease; or clinically evident edema
• Unstable, severe depression
• Serious conduction disorder, uncontrolled arrhythmia, or new Q waves or ST-segment depressions (>3 mm at rest or ≥2 mm with exercise)
• Abnormal kidney function (eGFR <30 based on serum creatinine, age, gender, and race)
• Anemia (Hb<13 g/dL in men; <12 g/dL in women)
• Drug abuse or excessive alcohol use (>7 drinks/week women; >14 drinks/week men)
• Use of any tobacco or nicotine products in the past year
• Osteoporosis (T-score < -2.5 on hip or spine scan)
• Regular use of growth/steroid hormones, sex steroids or corticosteroids, osteoporosis medication, or protein supplements
• Weight loss medications or procedures
• Current participation in another intervention study