Beetroot / Beet juice for Endurance
Beetroot juice and dietary nitrate produce a small but consistent improvement in submaximal endurance performance lasting roughly 2 to 30 minutes, especially in recreational athletes. The effect is unreliable for elite athletes, longer events over 30 minutes, and high-intensity interval training, and nitrate salt pills do not work.
Why this grade7-layer evidence engine
This earns a B (preliminary evidence) rather than a stronger grade because the high-quality evidence is consistent but the effect is small and clearly bounded. A 2022 systematic review (PMID 35580578, n=1705) found nitrate improved performance overall (SMD 0.101), and a 2022 meta-analysis (PMID 35892115, n=335) found chronic dosing helped 5-30 minute time trials (Hedges' g=0.30) but did nothing for 30-60 minute efforts. A 2025 umbrella review (PMID 40573069) confirmed non-athletes benefit most (SMD 0.26) with only a small VO2max gain (SMD 0.16).
The grade is capped by genuine counter-evidence. A meta-analysis of high-intensity interval training (PMID 34835931) found no improvement in peak or mean power (g=0.08, not significant), so the ergogenic effect appears mode-specific. A double-blind RCT in winter triathletes (PMID 35512758, n=80) cut oxygen cost and extended cycling time-to-exhaustion but showed no benefit in a 10-km skiing trial. Crucially, PMID 35580578 found beetroot juice and whole-diet nitrate work while nitrate salt supplements do not (p=0.629).
Regulators and clinics support safety more than performance claims. The FDA treats beet juice only as a food color, and the WHO addresses nitrate solely as a food additive (ADI 0-3.7 mg/kg), neither endorsing exercise benefits. The NHS notes the research dose (about 70 mL juice, 400 mg nitrate) and harmless beeturia, while Mayo Clinic links beet nitrates to athletic performance but stays cautious. This mix of modest, well-defined benefit plus a clear non-responding population justifies publishing with a warning.
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 = 0.713
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高階證據未達主導 (1 positive vs 1 negative)，由 raw_score 決定
- tier_strict_requirement_check — | A→B 因 scope.conflation_risk=true 且 L11 獨評較低 (B7-2 tier cap)
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status