For almost a decade, ketones have become one of the most talked-about and controversial supplements in endurance sports. In professional cycling, their use has spread to the point of being part of the nutritional arsenal of several WorldTour teams, even though the Union Cycliste Internationale (UCI) has just officially advised against their consumption. The reason: science does not support the claim that they improve performance or recovery.
However, the fact that they continue to be used despite their high cost and the lack of solid evidence raises an inevitable question: why have they become so popular among professionals if, according to studies, they don’t help improve performance?
The Origin of the Ketone Craze
It all started in 2016, when a study published by the University of Oxford in Cell Metabolism ignited the debate. In that study, a group of well-trained cyclists showed slight performance improvements after ingesting ketone esters before exercise, in combination with carbohydrates. Those results, disseminated in the media and at sports nutrition conferences, were enough for the term “ketone esters” to start circulating in the cycling community.
The appeal was easy to understand: an “alternative fuel” capable of providing energy when glycogen stores are low, without the side effects of ketosis induced by strict diets. The idea of a supplement capable of maintaining intensity when the body no longer has glucose available seemed revolutionary.
Shortly afterward, commercial products began to appear, especially in the road cycling world. WorldTour teams began experimenting with them in training and Grand Tours, and the industry responded with increasingly refined and, above all, expensive supplements.
Scientific evidence cools the enthusiasm.
Over time, other research groups attempted to replicate those initial results. The findings, however, were very different. Most subsequent studies did not observe significant improvements in performance or metabolic efficiency. In some cases, even neutral or negative effects were detected, especially when ketones partially displaced carbohydrate consumption during exertion.
The conclusion became progressively clearer: exogenous ketones offer no measurable performance advantages in endurance events. This is summarized by the UCI in its recent statement, which affirms that “there is no convincing evidence that ketone supplements improve performance or recovery” and that, therefore, it “does not recommend their use in cyclists’ nutritional plans.”
From performance enhancement to the promise of recovery
When the performance data failed to convince, the narrative shifted to another area: recovery. Some subsequent studies indicated that ketones could accelerate muscle glycogen resynthesis after exercise or increase endogenous EPO production, which could help the body respond better after intense efforts or consecutive stages.
This idea fit well with the reality of professional cycling, where recovery between stages is as crucial as performance itself. For a time, several teams opted to introduce ketones at the end of stages or on training load days, seeking that supposed “extra” regeneration boost.
However, more recent studies have also called this theory into question. A high-quality study with a large sample size published in recent months concluded that taking ketones after competition or training has no effect on the quality of recovery, neither on physiological parameters nor on markers of muscle fatigue.
An expensive but legal supplement
Despite the lack of solid evidence, ketones remain a common element in the nutrition of some teams. The explanation lies not so much in science as in the culture of elite sports: in professional cycling, any detail that can offer even the slightest advantage, however marginal or theoretical, is considered justifiable.
Furthermore, ketones are not prohibited by the World Anti-Doping Agency (WADA) or by the UCI itself. It’s a legal supplement with no documented serious adverse effects, so there’s no reason to penalize its use. The UCI simply advises against it, but doesn’t ban it. This leaves a gray area where each team can decide for itself whether or not to include it in its nutritional protocol.
The economic component adds even more interest to the debate. Exogenous ketone supplements are extremely expensive compared to other sports products. A bottle of ketone esters can cost between €100 and €150 for just a few doses, and some high-end products exceed €4 per serving. In terms of energy cost, they are far more expensive than any source of carbohydrates or protein.
That teams with multimillion-euro budgets continue to use them despite these prices suggests two things: either there is an internal belief that the effect can be real in specific situations (such as high mountain stages, altitude, or overload), or it is a matter of competitive caution, a “just in case” to avoid falling behind if rivals use them.
The psychological effect and the “just in case”
In practice, many sports nutritionists acknowledge that part of the success of ketones can be psychological. The simple act of ingesting something perceived as advanced technology or a cutting-edge resource can boost an athlete’s confidence. In disciplines where the mind plays a crucial role, this sensation can translate into improved performance, even if the physiological effect is negligible.
There is also an image component. In an environment where innovation and applied science are part of the teams’ discourse, forgoing a supplement that others use can be perceived as a lack of modernity or investment. Some teams have commercial agreements with ketone brands, ensuring their presence in the riders’ water bottles despite limited scientific evidence.
The UCI’s Position and the Future of Ketones
The UCI has clarified that its stance is not a ban, but rather a negative recommendation: until there is convincing evidence of their benefits, it sees no reason for their use. This decision comes after years of debate within the peloton, and coincides with the Movement for Credible Cycling (MPCC) having already recommended against their use some time ago.
The official position seeks, above all, to limit professional cycling’s dependence on supplements without scientific backing. In a sport that has suffered for decades from its relationship with performance-enhancing drugs, the UCI is trying to draw a line between innovation and nutritional speculation.
However, as long as ketones remain legal, safe, and expensive, their use will likely continue. In an environment where margins are so tight, any promise of improvement, however minimal, will remain attractive.
A supplement that symbolizes the times
Ultimately, the case of ketones reflects a persistent tension in elite sport: the gap between scientific evidence and real-world practice. Science calls for caution and conclusive data; teams, on the other hand, seek any potential advantage that the lab hasn’t yet fully validated.
Ketones symbolize that blurred boundary between what we know and what we want to believe. They may not improve performance or recovery, but their story explains better than any chart how the logic of high performance works: if something is legal, expensive, and promises even a minimal improvement, someone will use it, even if science says it does nothing.