## 4 Discussion
Therefore, the fasting participant activated our evolutionary heritage as hunter-gatherers, resulting in a progressively smaller weight loss that reflects greater metabolic efficiency. In our study, colorimetry results for the fasting participant showed significantly higher levels of dehydration compared to the control participant. The literature recommends drinking according to this in ultraendurance tests and maintaining a typical diet to stay properly hydrated [38]. Fluid replenishment should be accompanied by proportional sodium intake. Another key factor is that lower hydration during prolonged exercise increases reliance on carbohydrates as the primary fuel source [37]. Thus, the fasting participant may have had impaired nutritional strategy due to insufficient hydration, which does not promote fat utilization during exercise [37]. Moreover, despite the consumption of salts, dehydration was greater, suggesting that the participant did not drink enough during the test. Regarding the other urine markers (nitrates, glucose, and pH), no differences were observed between the two participants. However, protein presence in the urine of the fasting participant was higher at the end of the third and fourth days, the hottest days. This is related to muscle breakdown and protein catabolism [23]. However, in a fasting state, the degradation of muscle proteins is reduced [32]. Additionally, there is a higher risk of acute kidney injury when heat stroke is associated with hot weather and prolonged exercise [39]. Therefore, hydration and fasting should be carefully controlled, especially in excessively hot climates. The combination of prolonged exercise in a hot environment combined with dehydration from fasting can lead to an undesirable situation for the health of ultraendurance athletes. In our study, we observed a noticeable reduction in body weight for both participants. While increased physical activity undoubtedly played a significant role, it is essential to consider other contributing factors. The caloric restriction experienced, particularly by the fasting participant, dehydration, and potential lean body mass loss could all have influenced this weight reduction. Reflecting on the hunter-gatherer lifestyle we simulated, these weight fluctuations might mimic the natural variations our ancestors underwent as they navigated periods of food abundance and scarcity. Further investigations are essential to elucidate the specific contributions of each of these factors to the observed weight changes in such scenarios. Evolutionary implications of the findings from this study shed light on the adaptability and challenges faced by hunter-gatherer populations in their physically demanding lifestyles. The observation of increased sympathetic modulation and central fatigue in response to the multi-stage ultraendurance test aligns with the evolutionary fight-or-flight response seen in ancestral humans facing stressful situations [40]. The ability of the fasting participant to maintain stable glucose values and adapt to energy reserve economy supports the idea of physiological adaptations developed over millennia to cope with periods of caloric restriction and physical activity in ancestral hunter-gatherers [41; 42]. These findings suggest that the human body retains some of its evolutionary traits, which can be harnessed through fasting-based physical training to improve performance outcomes in extreme endurance events. Moreover, the study's demonstration of higher pain perception and dehydration in the fasting participant highlights the potential trade-offs and challenges faced by hunter-gatherer populations during periods of fasting and physical exertion. In ancestral times, access to sufficient hydration and nutritional resources might have been unpredictable, leading to potential compromises in physical performance and well-being during times of scarcity.