EFFECTS OF INCREASED ENERGY-INTAKE AND OR PHYSICAL-ACTIVITY ON ENERGY-EXPENDITURE IN YOUNG HEALTHY-MEN/

This study was designed to examine effects of alterations in energy ba lance on adaptive changes in components of total energy expenditure (T EE). Nineteen young healthy males were studied during a 10-day sedenta ry energy balance baseline period and then randomly assigned to one of four 10-day treatment groups: 1) no change in energy intake (EI) or p hysical activity (PA; energy balance at low energy flux), 2) EI increa sed by 50% with no change in PA (positive energy balance), 3) TEE incr eased by 50% by increasing PA, matched by a 50% increase in EI (energy balance at high energy flux), and 4) TEE increased by 50% by increasi ng PA with no change in EI (negative energy balance). TEE was measured with doubly labeled water, resting metabolic rate (RMR) by indirect c alorimetry, and thermic response to feeding (TEF) by indirect calorime try; energy expenditure of physical activity (EEPA) was estimated by s ubtracting RMR, TEF, and prescribed PA from TEE. TEE was significantly increased by PA (by design) but not EI. There was a significant main effect of intake and a significant intake-by-activity interaction for changes in RMR. In post hoc analysis, RMR was significantly increased during positive energy balance and energy balance at high energy flux relative to change in RMR when energy balance was maintained at low en ergy flux. A significant increase in RMR was also noted during negativ e energy balance after adjustment for change in fat-free mass. There w as no significant difference in change in RMR among the three treatmen t groups. There were no significant main effects of intake or activity on EEPA or thermic effect of a meal. These results suggest that in yo ung healthy males living under tightly controlled conditions 1) adapti ve changes in TEE in response to shortterm alterations in energy balan ce are mediated primarily through changes in RMR, 2) RMR can be elevat ed during a state of energy balance when energy flux is increased, and 3) magnitude of adaptive change in RMR is similar in response to incr eased EI and/or PA; therefore simultaneous increases in energy intake and physical activity do not act synergistically to raise RMR.