BCAA / Branched-Chain Amino Acids for Muscle Gain
High-quality reviews show that taking isolated BCAA supplements does not meaningfully increase muscle mass or strength; when overall protein intake is adequate, they add no extra benefit beyond complete protein.
Why this grade7-layer evidence engine
This claim earns a Counter-Evidence grade because the strongest available evidence points the same direction. A 2017 systematic review (PMID 28852372) concluded that the idea BCAAs alone stimulate muscle protein synthesis is "unwarranted," since BCAAs lack the other essential amino acids needed as building material. A 2021 review (PMID 33741748) likewise found that accumulated acute and long-term data do not support isolated BCAA or leucine as a meaningful strategy for hypertrophy or strength.
Newer syntheses agree. A 2025 systematic review of 22 trials (PMID 41346907) found only 1 of 5 body-composition studies showed muscle gains, calling the evidence inconsistent and equivocal. A 2024 overview of reviews (PMID 38241335) found BCAAs reduce post-exercise soreness and muscle-damage markers but provide no muscle-performance recovery benefit, and muscle gain was rarely even measured. A small crossover trial (PMID 28638350, n=10) showed a 22% rise in synthesis, but only versus placebo, not versus whole protein.
Regulators and clinics reinforce this. The EU's EFSA rejected all BCAA muscle and recovery claims for lack of an established cause-and-effect relationship, the US FDA lists BCAAs only as a safe nutrient supplement without any muscle health claim, and Mayo Clinic notes the precise role of BCAAs "remains to be defined" and that adequate dietary protein already meets needs.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.302
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 negative 主導 (2 negative > 0 positive)，下層 RCT 不能推翻
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status