Effects of a Second Bout of Strenuous Exercise on Appetite Regulating Hormones and Food Intake

Strenuous exercise typically shifts the hormonal milieu towards acute appetite suppression, which may persist for 30 min post‐exercise. Since no compensatory drive to eat occurs following exercise, a negative energy balance transpires. Although this exercise‐induced‐anorexia has been examined at different times of the day, it is still unclear whether a compensatory shift eventually occurs, or if this phenomenon is exacerbated with repeated exercise on the same day. This study investigated the effects of two bouts of strenuous exercise on appetite regulating hormones, perceptions of appetite, and food intake. In a randomized crossover design, 18 moderately fit (VO 2 max 44±6 ml·kg·min −1 ) Canadian Armed Forces members (14 male, 4 female) volunteered to complete two 8‐h trials. One trial involved completing two 2‐h circuits of military activities of varying intensities interspersed with 2 h of rest (EX), the other involved 8 h of rest (REST). Participants consumed military rations ad libitum during the trials, and were provided with a supper ration pack to consume at home. Visual analogue scales for appetite as well as venous plasma concentrations of GLP‐1, PYY, acylated ghrelin, and leptin were assessed throughout the trials. Participants expended significantly more energy during the EX trial, expending 1649±322 kcal during the 4 h of exercise vs. 404±68 kcal over the same time period during REST. Although the hormonal changes during EX favoured appetite suppression with: 1) elevated PYY levels during EX as compared to REST (53.9±13.8 pg/ml vs. 47.2±9.0 pg/ml), 2) supressed acylated ghrelin levels during EX as compared to REST (75.0±49.7 pg/ml vs. 109.6±59.4 pg/ml), and 3) larger increases in GLP‐1 levels from immediately following exercise to 1 h post‐exercise (3.3±2.7 pg/ml – 4.8±3.2 pg/ml), as compared to the equivalent time periods during the REST trial (3.6±1.6 pg/ml – 3.8±1.7 pg/ml); no significant differences were found between conditions for food energy consumed either during the eight hours in the lab (EX:2055±680 kcal vs. REST:1910±630 kcal), or during the subsequent meal consumed at home (EX:868±410 kcal vs. REST:1014±701 kcal). Similarly no significant trial effects emerged for any measure of appetite sensation. These results demonstrate that energy expenditure and energy intake remain uncoupled even following 2 bouts of arduous exercise. Hormonal responses following the second exercise bout were not significantly different from those found after the first exercise bout, suggesting the hormonal response following acute exercise can be reproduced throughout the day. Even when energy requirements increase by over 1200 kcal, energy intake over the entire day remains remarkably similar (EX: 2923±802 kcal vs. REST: 2924±1066 kcal). In the absence of a compensatory drive to eat, additional exercise bouts further augment the negative energy balance found during acute exercise. Support or Funding Information This research was funded in part by Defence Research & Development Canada (DRDC).

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