Eating persistently less than the body would freely choose, with nutrient intake kept complete. Cholesterol, blood pressure, inflammation and insulin handling improve, even in people whose numbers already look healthy. Bone, muscle, hormones and energy expenditure pay the cost, and nearly every harm tracks how deep the deficit goes. Lifespan itself remains unmeasured in people. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Body weight and waist circumference | 0.5–1.0% body weight per week; waist below 94 cm (men) / 80 cm (women) | Confirms the deficit is the intended size |
| Fat mass and appendicular lean mass (DXA) | Fat falling; appendicular lean mass index above 7.0 (men) / 5.5 kg/m² (women) | Separates fat loss from lean loss |
| Bone mineral density (DXA, spine and hip) | T-score above −1.0; no fall beyond scanner precision | Detects the best-documented harm before fracture |
| Fasting insulin | 2–5 µIU/mL | Most responsive marker of the metabolic benefit |
| HOMA-IR | Below 1.5 | Single index of insulin resistance |
| HbA1c | 4.8–5.4% | Glycaemic benefit over 3 months, not one morning |
| ApoB | Below 80 mg/dL (below 60 mg/dL if risk is elevated) | Counts atherogenic particles directly |
| Triglycerides | 50–80 mg/dL | Among the fastest-moving lipid responses to a deficit |
| hs-CRP | Below 0.5 mg/L | Inflammation falls only with sustained restriction |
| TSH and free T3 | TSH 0.5–2.0 mIU/L; free T3 upper half of range | Falling free T3 signals too deep a deficit |
| Total testosterone (men) | 500–900 ng/dL | Detects reproductive-axis suppression |
| Oestradiol and cycle regularity (women) | Cycles of 24–35 days; oestradiol appropriate to cycle phase | Earliest reproductive sign; drives bone loss |
| Haemoglobin and ferritin | Haemoglobin 13.5–15.5 (men) / 12.0–14.5 g/dL (women); ferritin 50–150 ng/mL | Anaemia was flagged for monitoring by trial safety data |
| 25-hydroxyvitamin D | 40–60 ng/mL | Supports calcium handling that offsets bone loss |
| Resting metabolic rate | Within 10% of prediction for current lean mass | Quantifies otherwise invisible metabolic adaptation |
| eGFR | Above 90 mL/min/1.73 m² | Guards against kidney strain at very low intake |
Cadence: Baseline panel; weight and waist weekly; blood pressure weekly for six weeks on antihypertensives; bloods at 3 and 6 months, then every 6–12 months; DXA at 12 months, then every 12–24 months.