An essential amino acid obtained from food and supplements. The most encouraging evidence points to modest gains in blood-sugar control, inflammation, and waist size, with weaker signals for skin and memory and only theoretical longevity support. Well tolerated at modest doses, but the evidence is thin. Avoid in liver disease; watch zinc balance. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Fasting glucose | 70–90 mg/dL | Tracks the core metabolic benefit |
| HbA1c | < 5.4% | Longer-term glycemic response |
| Fasting insulin / HOMA-IR | Insulin < 6 µIU/mL; HOMA-IR < 1.5 | Primary endpoint improved in trials |
| hs-CRP | < 1.0 mg/L | Captures the anti-inflammatory effect |
| Serum zinc | 90–120 µg/dL | Detects histidine-related zinc depletion |
| Serum copper | 80–155 µg/dL | Screens for chelation-related mineral shifts |
| ALT and AST (liver enzymes) | ALT < 25 U/L (men), < 20 U/L (women) | Safety screen; contraindicated if liver disease |
| BUN / ammonia | BUN 10–20 mg/dL; ammonia within lab normal | Reflects protein/ammonia handling |
| Complete blood count (hemoglobin) | Hgb 13.5–15 g/dL (men), 12–15 g/dL (women) | Relevant to red-cell/erythropoiesis role |
Cadence: Baseline before starting; recheck at 8–12 weeks, then every 6–12 months on long-term use