utilizing protein during weight loss to impact physical function

Conditions: Obesity; Weight Loss; Diet Modification; Aging; Weight Change, Body; Dietary Habits

Summary: 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