Physiological safety and Multi-Tissue metabolic adaptation under a novel intermittent prolonged fasting regimen

Prolonged fasting (PF)-induced hypometabolism shows significant potential for supporting human survival during long-term space missions and in extreme extraterrestrial environments. However, developing safe and effective PF protocols remains a critical challenge for practical application. In the present study, 6- to 7-week-old healthy male Sprague-Dawley (SD) rats were used to investigate PF and intermittent PF (IPF) regimens. Body weight (BW), resting energy expenditure (REE), blood glucose, and ketone body concentrations were measured across PF duration. Based on PF results, two IPF regimens were designed: the 6 + 6 IPF model (6-day fasting/6-day refeeding, repeated twice) and the 4 + 6 + 6 IPF model (4-day fasting followed by three cycles of 6-day refeeding/6-day fasting). Survival rates, food intake, BW, REE, blood glucose, ketone bodies, and metabolic transcriptional responses were analyzed across regimens. PF induced severe weight loss and metabolic switch from glucose to ketone body utilization between days 2- 5 of fasting. The 4 + 6 + 6 IPF model demonstrated superior safety compared to the 6 + 6 IPF model. The 4-day adaptive PF phase in the 4 + 6 + 6 IPF model enables rats to successfully restore BW, REE, blood glucose, and ketone body levels to normal during subsequent fasting-refeeding cycles. This recovery was supported by tissue-specific transcriptional and protein changes in genes related to fatty acid oxidation, lipogenesis, gluconeogenesis, and ketogenesis. Our findings provide evidence of a critical metabolic switch during PF and validated a safe and effective IPF model, contributing to the development of a fasting-induced hypometabolism application for extraterrestrial exploration, however IPF still needs in-depth research in addressing aerospace medicine issues.