Author(s): HÖCHSMANN, C., SALLER, M., FRODL, A., NUSSER, V., HECHENBICHLER FIGUEROA, S., KOEHLER, K., Institution: TECHNICAL UNIVERSITY OF MUNICH, Country: GERMANY, Abstract-ID: 166

INTRODUCTION:
Both the timing of exercise and the duration of pre-exercise fasting influence metabolic responses and energy balance. However, the combined effects of these factors on post-exercise energy intake and appetite regulation remain poorly defined. This study examined the independent and interactive effects of time of day and fasting duration on acute and 24 h post-exercise energy intake, subjective appetite, and substrate oxidation.
METHODS:
In a randomized five-condition crossover design, 35 healthy young adults completed three fasted exercise trials consisting of 30 min treadmill running at 65 percent of peak oxygen uptake: morning exercise following a 12 h overnight fast, evening exercise following a 6 h fast, and evening exercise following a 12 h fast. A subsample (n = 17) additionally completed fed morning and fed evening exercise sessions. Acute post-exercise energy intake was assessed using an ad libitum meal, while total energy intake over the subsequent 24 h was measured via weighed food records. Subjective appetite ratings were obtained before and after exercise, and substrate oxidation during exercise was determined by indirect calorimetry. Linear mixed models were applied for statistical analyses.
RESULTS:
Acute post-exercise energy intake differed significantly across fasted conditions, increasing from morning to evening exercise and being highest following evening exercise after a 12 h fast (p < 0.001). Total 24 h energy intake showed a similar pattern, with the greatest intake observed after evening exercise following prolonged fasting (p < 0.001). Hunger, desire to eat, and prospective food consumption were consistently higher, and fullness lower, after evening compared with morning exercise, paralleling intake responses. Substrate oxidation during exercise was strongly influenced by condition, with greater fat oxidation during fasted and evening exercise (p < 0.001). In the subsample, pre-exercise feeding altered substrate oxidation but did not attenuate acute or 24 h post-exercise energy intake or appetite responses.
CONCLUSION:
Prolonged fasting combined with evening exercise resulted in consistently greater compensatory energy intake, evident both at the post-exercise meal and across the subsequent 24 h, indicating a sustained rather than transient response. Although fasting and feeding altered substrate oxidation during exercise markedly, these metabolic shifts were not accompanied by corresponding reductions in post-exercise intake, supporting a dissociation between substrate use and behavioral energy compensation. Collectively, these findings indicate that temporal context and fasting-related factors play a dominant role in post-exercise appetite regulation, outweighing acute metabolic signals.