Submitted on December 18, 2006
Accepted on April 23, 2007
Thermic Effect of Food and Beta-Adrenergic Thermogenic Responsiveness in Habitually Exercising and Sedentary Healthy Adult Humans
Nicole R Stob1, Christopher Bell2*, Marleen A. van Baak3, and Douglas R. Seals4
1 Integrative Physiology, University of Colorado at Boulder, Boulder, Colorado, United States; Department of Integrative Physiology, University of Colorado-Boulder, Boulder, Colorado, United States
2 Department of Health and Exercise Science, Colorado State University, Fort Collins, Colorado, United States
3 Department of Human Biology, Universiteit Maastricht, 6200 MD Maastricht, Netherlands
4 Department of Integrative Physiology, University of Colorado-Boulder, Boulder, Colorado, United States
* To whom correspondence should be addressed. E-mail: cbell{at}cahs.colostate.edu.
The thermic effect of food (TEF) is an important physiological determinant of total daily energy expenditure (EE) and energy balance. TEF is believed to be mediated in part by sympathetic nervous system (SNS) activation and consequent beta-adrenergic receptor (
-AR) stimulation of metabolism. TEF is greater in habitually exercising compared with sedentary adults, despite similar postprandial SNS activation. We determined if augmented TEF in habitually exercising adults is associated with enhanced peripheral thermogenic responsiveness to -AR stimulation. In separate experiments in 22 sedentary and 29 habitually exercising adults, we measured the increase in EE (indirect calorimetry, ventilated hood) during -AR stimulation (intravenous isoproterenol: 6, 12, and 24 ng/kg fat-free mass (FFM)/min) and EE before and after a liquid meal (40% of resting EE; 53% carbohydrate, 32% fat, 15% protein). The increase in EE during incremental isoproterenol administration was greater (P=0.01) in habitual exercisers (0.34±0.03, 0.54±0.04, 0.81±0.05 kJ/min; mean±SE) compared with sedentary adults (0.26±0.03, 0.40±0.03, 0.64±0.04 kJ/min). The area under the TEF response curve was also greater (P=0.04) in habitual exercisers (160±9 kJ) compared with sedentary adults (130±11 kJ), and was positively related to -AR thermogenic responsiveness (r=0.32, P=0.02). We conclude that TEF is related to -AR thermogenic responsiveness, and that the greater TEF in habitual exercisers is attributable in part to their augmented -AR thermogenic responsiveness. Our results also suggest that peripheral thermogenic responsiveness to -AR stimulation is a physiological determinant of TEF and, hence, energy balance in healthy adult humans.
