Comprehensive Analysis of Biological and Metabolic Changes During a 10-Day Water-Only Fasting: A Case Study

Objective: Prolonged water-only fasting has garnered significant interest for its potential health benefits, including enhanced metabolic flexibility and cardiovascular improvements. This case study explores the physiological and metabolic responses of a healthy 36-year-old male during a 10-day water-only fast, followed by a structured 5-day refeeding phase.Methods: Key parameters such as heart rate variability (HRV), respiratory quotient (RQ), resting metabolic rate (RMR), oxygen consumption (VO₂), and sleep quality were monitored throughout the fasting and refeeding periods. Data collection was conducted at the Laboratory of Atatürk University Faculty of Medicine in February 2025.Results: Findings revealed substantial metabolic adaptations, including a decline in RMR from 2040 kcal/day to 1342kcal/day and a reduction in RQ from 0.89 to 0.74 by fasting day 7, indicating a shift from carbohydrate to fat oxidation. Cardiovascular parameters, including blood pressure and heart rate, remained stable, while sleep patterns exhibitednotable variability, with a marked reduction in deep sleep after the third day of fasting. During the refeeding phase, metabolic and physiological parameters progressively returned to baseline levels, underscoring the importance ofdietary reintroduction in restoring homeostasis.Conclusion: This study highlights the dynamic interplay between metabolic rate, substrate utilization, and cardiovascular stability during prolonged fasting and refeeding. While the findings align with existing literature, the resultsemphasize the individuality of fasting responses and the necessity for medical supervision. These insights contributeto the growing body of evidence supporting water-only fasting as a potentially safe and effective intervention for metabolic health, warranting further investigation in diverse populations.Cite this article as: Ulupınar S, Özbay S, Bedi̇r D, et al. Comprehensive analysis of biological and metabolic changes during a 10-day water-only fasting: A case study.Arch Health Sci Res. 2025; 12, 0058, doi: 10.5152/ArcHealthSciRes.2025.25058.