⚠️ Auto-extracted by Claude on 2026-05-26 — headline figures transcribed from the abstract + methods of the local PDF ; full Results/Discussion not yet verified. Numerics may be approximate.

Analysis of physiological and biochemical changes and metabolic shifts during 21-Day fasting hypometabolism

Dai Z, Zhang H, … Xin B, Li Y · Scientific Reports 2024; 14:28550 · DOI: 10.1038/s41598-024-80049-2

A Chinese space-medicine study (Astronaut Research and Training Center) of a 21-day complete water-only fast framed around survival/hypometabolism for long-duration spaceflight and disaster scenarios — not aging per se, but the deepest/longest medically-supervised human fast with full clinical-chemistry tracking, complementing the proteomic studies. Pre-registered (ChiCTR2100048399).

Design

• n = 13 healthy volunteers (8 men, 5 women; mean age 40.5 ± 9.7 yr; BMI 24.5 ± 3.1) selected from 336 applicants.
• 34-day protocol: 3-day baseline → 21-day complete fast (mineral water ad libitum only) → 5-day calorie-restricted refeeding → 5-day full-recovery diet. Continuous medical supervision (Longgang Central Hospital, Shenzhen).

Key findings

• Body weight −14.96 ± 1.55% over the 21-day fast.
• Resting energy expenditure −20.3 ± 11.13% — profound hypometabolic adaptation (the study’s central claim: humans down-regulate metabolic rate to conserve energy during prolonged fasting); respiratory quotient trended toward fat oxidation.
• Deep ketosis: blood ketones rose from 0.1 ± 0.04 → 6.61 ± 1.25 mmol/L; glucose fell ~21.6%.
• Hyperuricemia: serum uric acid roughly doubled (385.4 → 866.3 µmol/L) — a concrete, dose-related adverse metabolic effect of prolonged fasting (competition between ketones/lactate and urate for renal tubular excretion).
• Organ safety: most blood-count and liver indicators remained within normal range; cardiac function showed functional adaptive changes without structural damage.
• Conclusion: under medical supervision, healthy adults can tolerate up to 21 days of water-only fasting with metabolic adaptation and no damage to pivotal organs.

Notes and limitations

• Single-arm, n=13, no control group; aim is survival-physiology / spaceflight, not longevity — no aging-biomarker or proteomic endpoints.
• Useful to this wiki as the upper-duration anchor for human prolonged fasting and for the hyperuricemia and hypometabolism signals not emphasized in the proteomic studies.

Cross-references

• prolonged-fasting — intervention page (upper-duration / hypometabolism / hyperuricemia data)
• pietzner-2024-fasting-proteome · commissati-2025-prolonged-fasting-inflammation — the proteomic prolonged-fasting studies