Essential amino acid supplements deliver nine building blocks the body cannot make. The reliable signal is better walking, strength, or lean-mass holding in older or low-function people, during bed rest, and when calories are short—not muscle gain in well-fed adults. Extra powder is optional when protein is already enough. Inherited breakdown disorders and advanced kidney disease exclude some. (Full Review)
| Marker | Target | Why |
|---|---|---|
| eGFR | Stable vs own baseline; often ≥90 mL/min/1.73 m² | Nitrogen/urea handling |
| BUN | ~10–20 mg/dL, interpreted with creatinine | Excess amino acid oxidation |
| Fasting insulin | Often <8 µIU/mL in functional practice | Branched-chain/insulin-resistance watch |
| HbA1c | Often <5.4% as a tight functional target | Glycemic change on leucine-rich formulas |
| Homocysteine | Often <10 µmol/L (some use <8) | Methionine load |
| IGF-1 | No established target; track direction vs own age-typical baseline | Anabolic versus longevity tension |
| Plasma amino acids | No established supplement target; track vs own baseline | Excess leucine/BCAA signature |
| DEXA lean mass | Rise or hold vs own baseline | Composition outcome |
Cadence: Labs and performance at 4 weeks, 12 weeks, then every 6–12 months, or sooner if gastrointestinal symptoms, edema, or unexpected fatigue appear