How to Read an Ergogenic-Aid Claim: The Short Evidence-Backed List

Sports scientists grade an ergogenic-aid claim by the quality of the evidence behind it, not by the confidence of the label. When that filter is applied honestly, the list of substances with meaningful support for improving exercise performance is short, and creatine and dietary nitrate sit near the top of it. Even those show effects that are modest, dependent on dose and timing, and often smaller in people who are already well trained. This article explains how the grading works and why most claims never clear the bar. It is educational and not medical advice.

Why the list is so short

Thousands of products are marketed to athletes. A 2018 International Olympic Committee consensus statement, led by Ronald Maughan in the British Journal of Sports Medicine, reviewed the field and concluded that only a small set of dietary supplements had good evidence for a direct performance benefit: caffeine, creatine, specific buffering agents, and nitrate. That is a striking result. After decades of research and marketing, the substances that survive scrutiny can be counted on one hand.

The reason is not that scientists are hard to please. It is that most performance claims rest on weak foundations: a single small study, an unblinded design, a surrogate measure that never translates to real competition, or an effect that vanishes when the trial is repeated. Grading evidence is the discipline of asking whether a result would still stand if you looked at all the data instead of the most flattering slice.

What a strong claim actually looks like

The highest tier of evidence is not one dramatic study. It is a body of well-conducted randomized trials, pooled and weighed together, where the reviewers also assess how trustworthy each review is. Sports scientists increasingly use structured tools for this. A common one is AMSTAR-2, a checklist that rates a systematic review as high, moderate, low, or critically low confidence based on how it handled bias, study selection, and analysis.

Two 2025 umbrella reviews on dietary nitrate show the method in action. An umbrella review sits one level above a normal meta-analysis: it collects the meta-analyses themselves and judges their quality. A Sports Medicine umbrella review by Poon and colleagues synthesized 20 systematic reviews of nitrate and graded them with AMSTAR-2, finding that most scored low or critically low, a candid signal that even a real effect can rest on a shaky literature. A separate umbrella review in Nutrients by Tian and colleagues did the same for beetroot juice, the most common nitrate source, rating most of the underlying reviews as moderate to high quality.

When you read a claim, this is the shape you want to see behind it: not a single study that found something, but multiple randomized trials, pooled and quality-checked, pointing in the same direction. The absence of that structure is itself information.

Read the effect size, not the headline

Statistically significant does not mean large. The Poon review found that nitrate improved measures such as time to exhaustion and muscular endurance, but the pooled effect sizes were small to moderate, roughly a quarter to a half of a standard deviation depending on the outcome. The Tian review similarly described improvements in strength as negligible in magnitude even where they reached significance.

That distinction matters for a reader. A supplement can have a real, replicated effect that is still too small to notice in a recreational context, or that only shows up in one narrow task. A claim that leads with clinically proven language or a large percentage without telling you the baseline, the task, or the population is hiding the part that would let you judge it.

Dose, timing, and who was tested

Even a well-supported substance only works within the conditions that were actually studied. The nitrate reviews are specific about this. Poon and colleagues reported that benefits were more consistent with a minimum intake in the range of 6 mmol per day and with several days of chronic use rather than a single dose. Tian and colleagues described acute pre-exercise and multi-day protocols reaching defined nitrate levels.

Population matters just as much. Effects also tend to be more pronounced in non-athletes and recreationally active people than in highly trained individuals, consistent with a ceiling effect: the fitter the body already is, the less room a supplement has to add. Creatine research shows related nuance, with responses varying between individuals. The 2018 IOC panel made the general point plainly, noting that responses to supplements vary widely between people because of factors including genetics, the gut microbiome, and habitual diet. A claim that promises the same benefit to everyone is ignoring the data it cites.

The questions that separate signal from noise

You can apply the same filter a reviewer would without reading every paper. A few questions do most of the work:

• Is the claim backed by pooled randomized trials, or by one study, testimonials, or mechanism alone?
• Does it report an effect size and the exact task, or only a percentage with no baseline?
• Does it state the dose, timing, and the population that was tested, and do those match you?
• Does it acknowledge that responses vary, or promise a uniform result?
• Is the outcome real performance, or a lab surrogate that may not transfer?

Most marketed claims fail several of these at once. That failure is not proof a product does nothing, but it is a signal that the evidence has not been established, which is a different thing from established evidence of benefit.

A note on safety and purity

Evidence of a performance effect is separate from evidence of safety, and neither is guaranteed by a claim. The IOC statement flagged a specific hazard for competitive athletes: some supplements are contaminated with substances banned under anti-doping codes, and inadvertent ingestion can end a career. That is a reminder that reading a claim well means reading what it leaves out, including what is in the bottle. Anyone weighing a supplement should discuss it with a qualified clinician who knows their situation.