UCI medical director Xavier Bigard has said there is no scientific evidence that ketones improve performance, though the governing body currently recommends against their use pending further study.
In an interview with L’Équipe, he also acknowledged that it would be "complicated" for ketones to be added to the list of prohibited substances.
At the World Championships in September, the UCI announced that it had ordered a scientific study into the effects of ketones and it recommended that riders refrain from using them in the intervening period.
Teams who sign up to the additional, voluntary measures of the Movement for Credible Cycling (MPCC) had already agreed not to use ketones, and riders including Romain Bardet and Guillaume Martin have recently called for their prohibition across the peloton. Some WorldTour teams, including Deceuninck-QuickStep and Jumbo-Visma, have acknowledged that they use ketones.
"To date, there is no scientific evidence that ketone bodies improve performance," Bigard told L’Équipe. "Five studies and as many articles have been published. The first, dating from 2016, was misinterpreted. An improvement of about 15 percent had been mentioned, but that had been carried out in conditions of overtraining, which do not correspond at all to the reality of a race or even of training.
"None of the next four studies confirmed these results. In fact, the researchers from the University of Leuven, who conducted the first study, published a second one in 2020 showing that there was no improvement in performance under normal conditions. Another of these studies even showed a deterioration under certain conditions."
Bigard, who has been in his role since June 2018, cited the potential side effects to the digestive system when asked why the UCI currently recommends against the use of ketones in the peloton.
"The danger of these secondary effects is limited, but they do exist," he said. "And as long as there is this potential for side effects and there is no improvement in performance, I do not see why we would recommend its use. Therefore, we issued a notice of non-recommendation."
For a substance to be added to the WADA prohibited list, it must satisfy any two of three criteria, namely that it "has the potential to enhance or enhances sport performance", that it "represents an actual or potential health risk to the athlete", or that "it violates the spirit of sport". While Bigard noted that the UCI study of ketones has only just been commissioned, he found it difficult, on current evidence, to envisage the substance being prohibited outright.
"Honestly, given our current state of knowledge, it seems complicated," he said. "But because we are listening to feedback, we have commissioned a scientific study, and I am currently finalising the terms of reference before issuing the call for proposals before the end of the year.
"We have every reason to believe that ketones do not improve performance, but there are one or two points to be addressed: the dosage, i.e. the quantity ingested and the repetition of intake, and the type of ketone. There is perhaps a category that has not been sufficiently studied and we will look into it."
Asked why some teams would persist in ketones when it supposedly had no performance-enhancing qualities, Bigard said: "It remains a mystery. We can ask ourselves the question of whether it’s the placebo effect."
