Deliberately lowering dietary protein quiets the body's growth signals. It reliably lowers a key growth-promoting hormone and improves blood-sugar and metabolic markers, and its firmest benefit is slowing kidney disease. Favoring plant over animal protein tracks with modestly lower death rates. But past about age sixty-five it accelerates muscle loss and frailty, and may raise the risk of dying. (Full Review)
| Marker | Target | Why |
|---|---|---|
| IGF-1 | Mid-to-lower age-adjusted reference range | Primary target; tracks growth-signaling load |
| eGFR | >90 mL/min/1.73m² | Detects kidney impairment that changes the risk-benefit balance |
| BUN | ~7–18 mg/dL | Reflects protein/nitrogen load and kidney handling |
| Serum albumin | 4.0–5.0 g/dL | Guards against protein-energy malnutrition |
| Fasting insulin | 2–6 µIU/mL | Tracks the metabolic/insulin-sensitivity benefit |
| HbA1c | <5.4% | Reflects longer-term glucose control |
| hs-CRP | <1.0 mg/L | Tracks systemic inflammation, which restriction may lower |
Cadence: Baseline, then ~4–8 weeks after starting, then every 3–6 months; more frequent in older adults or kidney disease