The Physiology Of the WEight Reduced State (POWERS) study: assessing energy balance

Background/objectives We provide the rationale for and description of energy balance measures (i.e., energy intake and energy expenditure) in The P hysiology O f the WE ight R educed S tate (POWERS) study which aims to understand the contribution of the many factors that influence weight regain following behavioral weight loss. Methods The primary dependent variable is weight regain over 1 year following a 7% or greater supervised weight loss. The balance between energy intake and expenditure is the primary determinant of weight regain. Healthy adults (target n = 205), aged 25- < 60 years, with body mass index (BMI) 30- < 40 kg/m 2 are being recruited. Energy intake and expenditure phenotypes are measured prior to weight loss (baseline, BL), immediately following weight loss (T0), and then four (T4) and 12 months (T12) after weight loss. Weight stability is required before BL and T0 measurement periods. Weight change at T12 from T0 is the primary outcome variable. Energy intake is measured with serial doubly labeled water (DLW) measurements combined with dual x-ray absorptiometry (DXA) to assess changes in fat and lean mass; DLW is also used to measure twenty-four-hour energy expenditure (TEE). Components of TEE including resting energy expenditure (REE) and non-resting and activity energy expenditure (NREE and AEE), as well as skeletal muscle chemomechanical efficiency and grip strength are assessed. Self-reported dietary intake is assessed with interviewer-administered multiple-pass 24-hour food recalls. Discussion This manuscript describes the rationale for the methods chosen to assess energy balance and the analytical methods employed to normalize and express data in the setting of changes in body weight and composition immediately following behavioral weight loss and thereafter at 4- and 12-months post-weight loss.