Real-Time Glycaemic and Metabolic Adaptation During Unsupplemented Spiritual Fasting up to 30 Days: A Self-Controlled Observational Study

Background: Prolonged unsupplemented spiritual fasting (USF), complete caloric abstinence motivated by spiritual practice, is undertaken by many communities worldwide, yet its physiological consequences remain poorly characterized. No prior study has documented continuous real-time monitoring during free-living fasting beyond 10 days. Methods: We conducted a self-controlled observational study of 23 experienced Jain practitioners undergoing USF. Seventeen completed at least 8 days of fasting (11 completed eight days, six continued to 30 days); six discontinued early. Continuous glucose monitoring (CGM) and blood biomarkers at baseline (Day-0), post-fasting (Day-9), and 60-day follow-up (Day-69) were obtained. Mood was assessed daily using PANAS. Within-participant comparisons used both parametric and non-parametric t-tests. Results: CGM revealed near-complete suppression of glycaemic variability within 24-48 hours of fasting onset, sustained throughout with no clinical hypoglycaemia in either cohort. Blood biomarkers showed transient perturbation during fasting -- including rises in hepatic enzymes, bilirubin, uric acid, creatinine, and lipid fractions -- broadly reversible by follow-up (Day-69). hsCRP rose during fasting then fell below baseline at follow-up (5.52{+/-}13.67 to 3.68{+/-}13.18 mg/L, p=0.034). HDL significantly rose above baseline (45.71{+/-}112.32 to 48.97{+/-}111.19, p=0.045) and LDL similarly declined below baseline (122.33{+/-}132.10 to 106.96{+/-}131.62 mg/dL, p=0.035); and then both significantly improved by follow-up. Thyroid axis suppression fully normalized by follow-up. Psychological wellbeing was maintained throughout. Conclusions: Extended USF produces a safely reversible pattern of acute physiological adaptation with net cardiometabolic benefit. Absence of clinical hypoglycaemia during 30-day water-only USF, documented here for the first time with CGM, provides empirical grounding for future controlled trials.