Utilizing Protein During Weight Loss to Impact Physical Function

This study will evaluate the effects of diet composition (i.e., amount of protein and carbohydrate) during a 6-month weight loss intervention and 12-months of follow-up on physical function, muscle mass, and weight loss maintenance in obese older adults. Participants will receive either a protein or carbohydrate supplement along with a behavioral weight loss intervention.

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.

Eligibility Criteria:
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