• Peta J Kelly, Kym J Guelfi, Karen E Wallman, and Timothy J Fairchild.
• School of Sport Science, Exercise and Health, The University of Western Australia, Perth, Australia.
• Med Sci Sports Exerc. 2012 Mar 1; 44 (3): 516-24.

PurposeIt has now been established that exercise performed under various environmental conditions may affect acute energy intake and appetite-related hormones. The exact mechanism linking acute energy intake and exercise remains unknown, although indirect evidence suggests a possible role for hydration status. Therefore, the purpose of this study was to investigate the interaction of exercise and hydration status on subsequent energy intake and appetite-related hormones.MethodsIn a randomized, counterbalanced design, 10 physically active males completed three experimental trials in a fasted state: exercise when hydrated (0%-1% of body mass), exercise when dehydrated (-1% to -2% of body mass), and a hydrated resting control. Exercise consisted of treadmill running for 45 min at 70% VO2peak. Participants were then given access to a buffet-style breakfast from which they could consume ad libitum. Blood was sampled regularly during trials for appetite-related hormones.ResultsThere were no significant differences in total energy intake between trials (P = 0.491); however, relative energy intake was significantly higher in the control (4839 ± 415 kJ, P < 0.001) compared to hydrated (1749 ± 403 kJ) and dehydrated exercise (1656 ± 413 kJ) conditions. Exercise performed in a dehydrated state resulted in significantly lower concentrations of ghrelin compared with control (P = 0.045) and hydrated exercise conditions (P = 0.014).ConclusionsExercise significantly decreased relative energy intake compared with resting control; however, energy intake (relative and total) was no different between the exercise conditions (dehydrated vs hydrated). Despite similar energy intake between trials, exercise in a dehydrated state resulted in a significantly lower concentration of ghrelin, a hormone responsible for stimulating appetite.

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