Ketones in the Peloton: Legal Supplements and the Grey Zone

Timeline

1. 2016A study suggests ketones taken before or during exercise could improve cycling performance; later studies do not confirm it.
2. 2019Jumbo-Visma acknowledges using ketones, according to Cyclingnews; other teams follow.
3. May 3, 2021According to the MPCC, the UCI confirms it is aware of widespread ketone use and promises a quick decision.
4. Jan 2023A study reports higher EPO concentrations after intravenous ketone infusion following intense cycling.
5. Jan 18, 2024A team manager calls on the UCI to ban ketones, saying they are 'bad for cycling's credibility.'
6. Oct 20, 2025The UCI states it does not recommend ketone supplements; they remain legal.
7. Dec 22, 2025The MPCC says its members will not use ketones or accept ketone sponsorship and calls for firm UCI rules.

The ethical issues

• Rules vs. spirit: using legal substances to seek an edge.
• Credibility and perception in a sport with a doping history.
• Unknown long-term health effects.
• Uneven rules: voluntary bans binding some teams but not others.
• Commercial promotion of supplements by riders.

Stakeholders

Stakeholder	Interests & obligations
Riders	Performance, health and fair competition.
Teams using ketones	Recovery and competitive advantage.
MPCC teams	A level field and the sport's credibility.
The UCI	Rider health and the sport's credibility.
WADA	An evidence-based Prohibited List.
Sponsors and supplement brands	Reputation and sales.

The case

Professional cyclists can often be seen drinking from small bottles after races. Many contain ketone supplements, which are legal and not on WADA’s Prohibited List.^[2] Ketones have nonetheless divided the peloton for years, and in October 2025 the UCI said it saw “no reason for them to be used.”^[1][2]

Background

Ketones are compounds the body produces and that muscles use when glucose is in short supply. They can also be taken orally as supplements.^[1] According to the UCI, ketone use became popular in endurance sports after a 2016 study suggested they could improve cycling performance. Later studies did not confirm this, and the UCI said there is “now a consensus that such supplements have no effect on performance during endurance exercise.”^[1] Further studies suggested benefits for recovery, including faster glycogen resynthesis and natural EPO production. A January 2023 study, for example, reported higher EPO levels after intravenous ketone infusion following intense cycling; intravenous use would conflict with cycling’s no-needle policy, but the researchers suggested oral drinks would likely have the same effect.^[4] The UCI said a “very comprehensive, high-quality study” later found no effect on recovery.^[1]

According to Cyclingnews, Jumbo-Visma acknowledged using ketones in 2019 and several other teams followed.^[3] Members of the MPCC (Movement for Credible Cycling), a voluntary clean-cycling movement of teams, are barred from using ketones, creating a divide in the peloton.^[3] Riders including Romain Bardet, Thibaut Pinot and Guillaume Martin called for a ban.^[3]

What the studies say

The 2016 study the UCI referred to was published in Cell Metabolism by researchers at Oxford and Cambridge, with co-authors from UK Sport and the U.S. National Institutes of Health. Across five studies of 39 high-performance athletes, they reported that a ketone-ester drink “improves physical endurance by altering fuel competition,” lowering lactate and shifting muscles toward burning fat even with normal glycogen stores.^[5]

Later research focused on recovery and adaptation. In a 2023 study in the Journal of Physiology, a KU Leuven group gave 18 healthy male volunteers either 25 grams of ketone ester or a control drink after each session of a three-week overload block of ten training sessions a week. In the ketone group, capillary contacts in muscle rose 44% and serum erythropoietin (EPO), the hormone that stimulates red blood cell production, rose 26%; the authors suggested ketones “may evolve as a potent nutritional strategy to facilitate recovery.”^[6] Dutch cycling media reported the EPO finding widely.^[4] The study was small, did not involve professional riders, and measured EPO and capillaries rather than race performance.^[6]

Pooled evidence on performance did not support the early enthusiasm. A 2022 systematic review and meta-analysis by University of Ottawa researchers in the International Journal of Sport Nutrition and Exercise Metabolism screened 569 articles. It included eight randomized controlled trials with 80 participants, 77 of them men, and found “no significant differences” in endurance performance between ketone and control trials, whether measured by time to exhaustion or by time trial. The authors concluded that ketone precursors and monoesters “do not exert significant improvements on endurance exercise performance,” although every study reported that the supplements raised blood ketone levels.^[7]

The credibility argument

In January 2024, the manager of the TotalEnergies team called on the UCI to ban ketones. “Ketones are a grey zone in cycling. It’s not good for our sport’s credibility and attractivity,” he said. “Teams who say they take ketones pretend they’re not enhancing performances. So why do they take them?”^[3] He argued that a ban could avoid possible long-term health risks and help cycling attract sponsors concerned about “rules, ethics and transparency,” and urged sponsors to tell teams to stop using them.^[3] The UCI’s medical director had acknowledged that banning ketones would be “complicated.”^[3]

The rules and governance

Ketones are not prohibited by WADA, and so not by the UCI’s anti-doping rules.^[2][3] On October 20, 2025, the UCI issued a declaration: “As there is no compelling evidence that ketone supplements enhance performance or recovery, the UCI sees no reason for them to be used. Therefore, the UCI does not recommend the inclusion of such supplements in riders’ nutritional plans.”^[1] Cyclingnews noted that the position is “only a recommendation”: ketones remain legal and will not be tested for.^[2] (Cyclingnews reported in 2024 that the UCI had issued an earlier “notice of non-recommendation” in 2021, while its 2025 report described the declaration as the UCI’s first stated position. The MPCC also refers to an earlier UCI “notice of non-recommendation.”)^[2][3][9]

The MPCC’s rule is more binding for its members, which Cyclingnews reported include eight men’s WorldTour teams and four women’s WorldTour teams, though it understood some MPCC-affiliated riders had continued to use ketones.^[2]

The MPCC had pressed the issue for years. After its board met during the 2021 Critérium du Dauphiné, it said the UCI had confirmed on May 3 that it “was aware of the prevalent use of ketone-based dietary supplements” and had promised a quick decision. The MPCC said international bodies “still have not reported any progress” and backed its member teams’ “commitment to the non-use of ketones.”^[8] On December 22, 2025, it called the UCI’s renewed position a recommendation “rather than the introduction of a formal medical rule or anti-doping regulation,” one that “does not close the debate.” It said many teams and riders had ignored the earlier non-recommendation, “with some even forming partnerships with ketone suppliers.” It also reported that a majority at its October 22 annual general meeting had agreed that members would “echo UCI’s recommendation to not use ketones” and would not accept ketone sponsorship. The MPCC urged the UCI to set “a clear and regulated position” on products in the “grey area” not yet banned by WADA.^[9]

Why the Prohibited List does not settle it

The World Anti-Doping Code sets the test for banning a substance. Under Article 4.3.1, WADA may consider adding a substance to the Prohibited List if, “in its sole discretion,” it finds that the substance meets any two of three criteria. The first is evidence that it “has the potential to enhance or enhances sport performance.” The second is evidence that its use “represents an actual or potential health risk to the Athlete.” The third is WADA’s determination that its use “violates the spirit of sport.” Once WADA has decided, its choice is “final” and cannot be challenged on the ground that a substance fails those criteria.^[10]

That framework explains why the ketone debate has continued for so long. Both sides of the performance argument have studies on their side: the early Oxford research, the KU Leuven findings on EPO and capillaries, and the meta-analysis that found no endurance benefit.^[5][6][7] The UCI’s own declaration rests on the view that there is “no compelling evidence” of a benefit to performance or recovery.^[1] The TotalEnergies manager raised possible long-term health risks, but he did not cite evidence of harm.^[3] The MPCC’s case rests mainly on credibility and on what it calls the escalating medicalisation of the sport, which comes closest to the “spirit of sport” criterion.^[9] Ketones do not clearly meet two criteria, and the governing bodies’ only statement so far has been a recommendation. That leaves riders and teams to draw the line themselves.^[1][2][9]

Aftermath

Ketones remained popular, and ketone brands sponsored riders and appeared in their social media and on cycling podcasts.^[2]

The core dilemma

Ketones are legal and, according to the UCI, unproven. Some teams use them anyway; others are barred by voluntary rules; and critics say the grey zone undermines credibility. Should sport ban a legal substance on grounds of perception, health uncertainty and fairness, or leave athletes free to use it?

Competing values

• Freedom vs. precaution: athletes’ choice of legal supplements against unknown health risks.
• Evidence vs. perception: acting on proof against protecting credibility.
• Fairness: uneven voluntary rules against a single standard.
• Commerce vs. integrity: supplement sponsorships against the sport’s image.

Strongest arguments

For a ban: the sport’s history makes credibility vital. Teams use ketones because they hope for an edge, and voluntary bans create unfair splits. Unknown long-term effects justify precaution.

Against a ban: ketones are legal, naturally occurring and, per the UCI, ineffective. Banning substances because of perception would set a broad precedent, and enforcement would be difficult.

For the UCI’s middle path: recommend against use, inform riders with evidence and leave the Prohibited List to WADA’s criteria.

Applying the frameworks

Virtue ethics

A virtue lens asks whether using a legal substance in hope of an edge reflects the spirit of sport or a culture of gamesmanship, and what integrity requires of teams.

Utilitarianism

A utilitarian lens weighs the possible benefits and harms of ketones against the costs of a ban and the benefits of improved credibility.

Justice

A justice lens asks whether it is fair that some teams are bound by voluntary rules while others are not, and whether a single standard would be fairer.

Walk it through: the Simple Decision Model

1. Spot the issue. You manage a WorldTour team deciding whether to use ketones. Stakeholders include riders, sponsors, rivals and fans. Less visible are amateurs who copy pros. The codes are the World Code, UCI rules and any MPCC commitments.
2. Gather facts. What does the evidence show about benefits and risks? What do sponsors expect? Beware the bandwagon effect.
3. Test options. (a) Use ketones. (b) Stop using them. (c) Stop using them and support a uniform rule.
4. Check codes and law. Check WADA’s list, the UCI declaration and your team’s commitments.
5. Decide and document. Explain the decision to riders and sponsors.
6. Communicate and follow up. Be transparent about supplement policies and review them as evidence develops.

What’s settled and what’s contested

• Settled: ketones are legal; the UCI recommends against them; MPCC members are barred.
• Contested: whether ketones help recovery; whether perception justifies a ban; when the UCI first stated its position.

Why this case matters

Ketones show how sport handles grey zones: legal substances with unproven benefits, uneven voluntary rules and credibility concerns. The case is a study in rules versus spirit.

Key terms

Rules vs. spirit of the game

Rules are the written minimum; the spirit is the fairness and respect the rules exist to protect. Rules set the floor; spirit sets the ceiling.

Legal but unethical

Law sets out what can be punished; ethics asks what is right. Compliance is a minimum, so an action can be lawful and still wrong.

Gamesmanship

Pushing the rules to their limits, without technically breaking them, to gain an edge. It tests, and can erode, the game.

Trust

The public’s belief that what they are watching is real. Integrity failures are ultimately failures of trust.

Commercialization

The process of turning sport into a product and a business enterprise, with profit pressures that can compete with principle.

Paternalism (hard and soft)

Restricting someone’s choices for their own good. Hard paternalism overrides competent, informed adults; soft paternalism steps in when information or autonomy is compromised.

Definitions from the Ethics Cases glossary.

Discussion questions

1. A team manager asked: if teams say ketones don't enhance performance, 'why do they take them?' Is seeking an unproven edge with a legal substance ethically different from doping?
2. Should a sport ban a legal substance mainly because it harms the sport's credibility?
3. MPCC teams cannot use ketones, but others can. Is a voluntary ban fair to the teams that follow it?
4. Is it appropriate for riders to promote supplements on social media while their governing body recommends against them?

Sources

1. UCI declaration concerning the use of ketone supplements by cyclists — Union Cycliste Internationale
2. UCI recommends against use of legal ketone supplements among professional cyclists due to lack of evidence of performance benefits — Cyclingnews
3. 'Ketones are bad for cycling's credibility' warns TotalEnergies team manager — Cyclingnews
4. Nieuwe studie: 'Inname ketonen zorgt voor verhoogde EPO-concentratie in het bloed' — Wieler Revue
5. Cox PJ et al., Nutritional ketosis alters fuel preference and thereby endurance performance in athletes, Cell Metabolism 24(2):256-268 (2016) — PubMed (National Library of Medicine)
6. Poffé C et al., Exogenous ketosis elevates circulating erythropoietin and stimulates muscular angiogenesis during endurance training overload, Journal of Physiology 601(12):2345-2358 (2023) — PubMed (National Library of Medicine)
7. Brooks E et al., Acute Ingestion of Ketone Monoesters and Precursors Do Not Enhance Endurance Exercise Performance: A Systematic Review and Meta-Analysis, Int J Sport Nutr Exerc Metab 32(3):214-225 (2022) — PubMed (National Library of Medicine)
8. Press Release – 2th June 2021 — MPCC (Mouvement Pour un Cyclisme Crédible)
9. The MPCC appeals to the UCI to establish firm rules to stop the escalating medicalisation of the sport (Dec. 22, 2025) — MPCC (Mouvement Pour un Cyclisme Crédible)
10. World Anti-Doping Code 2021 — World Anti-Doping Agency