Beetroot juice helps endurance a little — and least for the fittest athletes

Dietary nitrate — the active ingredient in the beetroot shots sold to endurance athletes — produces a small, real improvement in some measures of aerobic performance, and a negligible one in others [s1][s2]. The catch that matters most is who it works for: the boost is largest in recreationally active people and fades toward nothing in the highly trained athletes the product is marketed to [s2][s3].

Nitrate from beetroot and leafy greens is converted in the body to nitrite and then nitric oxide, a signalling molecule that widens blood vessels and appears to make muscle contraction more oxygen-efficient. The theory is sound and the biology is measurable. The performance question is narrower: how much faster, or how much longer, does it actually let someone go — and for whom.

A small effect, unevenly distributed

The foundational synthesis is a 2016 meta-analysis by Nathan McMahon and colleagues at the University of Queensland, which pooled 76 trials from 47 studies [s1]. Averaged across every endurance protocol, the effect was trivial and not statistically significant (effect size -0.10, 95% CI -0.27 to 0.06) [s1]. But splitting by test type mattered. In time-to-exhaustion trials — holding a fixed workload until you can't continue — nitrate produced a small-to-moderate, significant benefit (effect size 0.33, 95% CI 0.15 to 0.50, from 22 trials) [s1]. In graded exercise tests it was small and non-significant (0.25, 95% CI -0.06 to 0.56, from 8 trials), and in the 28 time-trial protocols, the ones that most resemble a race, the pooled effect did not reach significance [s1]. The pattern — help with capacity, less help with racing — has largely held since.

A 2026 meta-analysis narrowed the lens to maximal oxygen uptake across 38 studies and 703 participants, and put the average gain at a small but clearly significant standardised mean difference of 0.24 (95% CI 0.11 to 0.37) [s2]. The subgroup split is the story. In recreationally active participants the effect was 0.38; in highly trained athletes it was 0.07 (95% CI -0.09 to 0.23) — statistically indistinguishable from no effect [s2]. The authors also flagged funnel-plot asymmetry consistent with small-study effects, meaning the true average is, if anything, likely to be smaller than the pooled figure [s2].

The elite paradox

That leaves a gap between the marketing and the evidence for exactly the customers most likely to buy. A 2026 scoping review of randomised trials restricted to highly trained and elite athletes — 31 RCTs in all — found the results genuinely inconsistent [s3]. Benefits turned up most often for cycling time-trial performance, Yo-Yo intermittent recovery running, anaerobic power and recovery, but findings for endurance performance and oxygen consumption were mixed, even when nitrate and nitrite levels in the blood rose as expected [s3]. Supplementation protocols in those trials varied widely, from 4 to 19.5 mmol of nitrate a day (248 to 1,209 mg) and from a single dose to 15 days [s3] — variation that makes a clean verdict for elite sport hard to reach.

Why the fittest respond least is not fully settled, but the leading explanation is that well-trained muscle is already highly efficient at using oxygen and producing its own nitric oxide, leaving less room for a dietary nudge to add. For a trained athlete, the plausible margin is small enough to sit inside the noise of a real race.

What the evidence supports

The defensible reading is modest and specific. Dietary nitrate can produce a small improvement in oxygen uptake and in how long submaximal effort can be sustained, most reliably in recreational and sub-elite exercisers, using standard doses in the region of 6.4 to 12.8 mmol taken for at least three consecutive days [s2]. It is not a large effect, it is least dependable in time-trial and race-type efforts, and it is weakest in the elite athletes to whom it is most aggressively sold [s1][s2][s3]. Unlike some ergogenic aids it carries little known downside beyond cost and, for some people, stomach upset — but "probably harmless and occasionally helpful" is a fair summary, not "performance-enhancing" in the sense the label implies.

Nitrate sits alongside a short list of supplements with genuine, bounded evidence, a group that also includes caffeine, whose sprint effect is real but small and creatine, whose case has firmed up. It contrasts with claims built on the same nitric-oxide biology but far thinner data, such as nasal-only breathing for performance. And because the fittest gain least, the returns on nitrate should be read against what actually drives aerobic fitness in the first place — training, not the drink taken before it.