Fasting changes when food is eaten, not what. Human evidence supports modest weight and fat loss, steadier blood sugar, better blood fats and blood pressure, and less liver fat — working about as well as eating fewer calories. Longevity claims stay unproven in people. Main downsides: early hunger, muscle loss, and risks for those on medication. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Fasting glucose | 70–85 mg/dL | Tracks blood-sugar control and fasting response |
| HbA1c | 4.8–5.4% | Average blood sugar over ~3 months; key metabolic marker |
| Fasting insulin | 2–5 µIU/mL | Detects insulin resistance earlier than glucose |
| Triglycerides | <80 mg/dL | Reflects metabolic and lipid response to fasting |
| HDL cholesterol | >55 mg/dL (>60 in women) | "Good" cholesterol; cardiovascular protection |
| LDL cholesterol | Context-dependent | "Bad" cholesterol; cardiovascular risk |
| hs-CRP | <1.0 mg/L (optimal <0.5) | Marker of systemic inflammation |
| ALT / AST | <25 U/L (ALT) | Liver enzymes; track fatty-liver improvement |
| Blood pressure | <120/80 mmHg | Monitors cardiovascular benefit and over-lowering |
| Body composition (DEXA) | Maintain or increase lean mass | Ensures weight lost is fat, not muscle |
| Electrolytes (sodium, potassium, magnesium) | Mid-normal range | Guards against depletion during longer fasts |
Cadence: Baseline, then ~8–12 weeks, then every 6–12 months; more frequent glucose checks when adjusting diabetes medication.