Full fasting, an old healing practice, means going without all food for a day to several weeks while drinking water. Weight loss is reliable; repeated short fasts roughly match daily calorie restriction. Other benefits rest mostly on studies without comparison groups; blood-test gains tend to fade within months. Costs include fatigue, muscle loss, a temporary cholesterol rise and sharply higher danger with diabetes or blood-pressure drugs. Long-term value remains unproven. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Sodium | 135–145 mmol/L | Safety: low blood sodium stops the fast |
| Potassium | 3.5–5.0 mmol/L | Safety: low values signal refeeding risk |
| Phosphate | 2.5–4.5 mg/dL | Safety: falls on refeeding |
| Magnesium | 1.7–2.2 mg/dL | Safety: falls during long fasts |
| Uric acid | 3.5–7.2 mg/dL | Safety: expected to rise; matters with gout |
| Creatinine | 0.6–1.3 mg/dL | Safety: kidney function |
| Glucose | 70–99 mg/dL fasting | Expected to fall; safety with diabetes drugs |
| Beta-hydroxybutyrate | Below 0.4 mmol/L | Expected to rise; marks adherence |
| LDL cholesterol | No established target during a fast; compare post-refeeding value with own baseline | Expected to rise |
| Blood pressure | Below 120/80 mmHg | Expected to fall; safety for low blood pressure |
| QTc on ECG | 450 ms or less in men, 460 ms or less in women | Safety: prolongation precedes arrhythmia |
| Fat-free mass | No established target; track change from own baseline | Expected to fall, then recover |
| Chloride | Not specified in the ER | Safety: paired with sodium |
Cadence: Baseline before a multi-day fast; during fasts longer than 3 days, blood pressure and symptoms daily, electrolytes every 2–3 days, regular ECGs in very long fasts; after refeeding, lipids, uric acid and body composition at 2–4 weeks and 3 months