Trajectory of Psychological Adaptation During an 8-Day Fast: Changes in Subjective Well-Being, Mood, and Neuroendocrine Responses

Background/Objectives: Prolonged fasting induces substantial metabolic and neuroendocrine adaptations; however, less is known about the accompanying psychological changes. This study evaluated changes in subjective well-being and mood during an 8-day fast in relation to serum concentrations of α -endorphin, serotonin, oxytocin, and cortisol. Methods: Fifteen male subjects in good health completed an 8-day fast. Subjective well-being was assessed each day using a comparative self-rating scale, and mood was evaluated using the Polish version of the UWIST Mood Adjective Checklist (UMACL). Serum concentrations of α-endorphin, serotonin, oxytocin, and cortisol were measured before and after the fast, both at rest and following a maximal exercise test on an ergometer. Results: Subjective well-being gradually improved during the fasting period, and tense arousal, a dimension of mood, decreased. No significant changes were observed in energetic arousal or hedonic tone. The combination of fasting and exercise was associated with significant increases in α-endorphin, serotonin, and cortisol concentrations. Fasting was associated with a significant increase in post-exercise cortisol concentrations, whereas exercise after fasting was associated with a significant increase in serotonin concentrations. Despite concurrent psychological and hormonal adaptations, no consistent relationships were found between changes in hormone concentrations and psychological variables. Conclusions: Prolonged fasting was accompanied by gradual psychological adaptation, reflected in improved subjective well-being and reduced tension, whereas exercise under these conditions was associated with neurohormonal changes. These changes were associated with the coordinated activation of multiple neuroendocrine systems, suggesting that psychological and neuroendocrine adaptations represent complementary responses to prolonged metabolic stress rather than being opposing processes.