Paris (AFP)

The Jumbo team recognizes using them, their effects on performance and the health risks are debating: what are ketones, which make people talk about the Tour de France?

. How it works ?

Ketones are "a natural substrate produced by the liver from lipids (fats) when our body lacks carbohydrates (sugars)," says Jean-Jacques Menuet, the doctor Arkéa-Samsic team.

This mechanism can be caused naturally by a "diet" effective to cause a rapid weight loss, but also by the ingestion of ketones produced out of the body, continues the specialist.

What Oxford researchers in England managed to create several years ago, culminating in a dietary supplement, in the form of vials containing a translucent liquid, mostly yellow, pure or diluted.

. What interest for the pro cyclist?

In addition to allowing weight loss if they are used during training, ketones are very interesting in the short term, ensure team doctors.

"When you make low-intensity efforts, you use lipids (fats), and when you make a big effort, by rolling to block, your body uses rather carbohydrates", develops for AFP Simon Verdonck, the doctor of the Cofidis team.

"The intake of ketones can delay the use of carbohydrates, saving them for the final stage." To accelerate in a final ascent, for example. "It's an extra fuel for the muscle," simplifies Jean-Jacques Menuet.

. Who uses them?

If we talk about it so much, it is because the manager of the Jumbo-Visma team, victorious of four of the first eleven stages of the Tour, has recognized their use in an article of the Dutch newspaper De Telegraaf.

"Ketones are a dietary supplement and you can use it as a vitamin," said Richard Plugge. "It's nutrition, it's a supplement," said Wednesday the sports director of the team Frans Maassen, indicating "do not know" since when its riders used.

"It's been about five years that we hear about it," says Simon Verdonck the doctor Cofidis. "Since then, many other teams have started to use them, but we do not use them yet."

"It's democratized," says Jean-Jacques Menuet. "At first, it cost several thousand euros per liter, today we find on the internet for 30 to 90 euros the bottle".

. Is it dangerous?

The effects of the intake of ketones remain mysterious in the long term. "The studies are not unequivocal," notes Simon Verdonck. "It may be in the future to be part of cycling" but "while the other teams are testing, we prefer to watch the studies and we will see".

Same story for the doctor Arkéa-Samsic, who refuses to prescribe. "I do not want to receive in ten years a courier of a runner telling me that he has the liver in bulk," asserts Jean-Jacques Menuet. "If you prove to me that taking ketones is totally harmless, maybe I'll have a slightly more benevolent and permissive attitude."

Other danger according to the specialist: being for the moment considered as food supplements, the ketones and their use sometimes escape the medical radars. "It's not because the doctor does not prescribe that the runner will not take," he says, alerting on "the lack of methodology" that may exist.

. What is the position of WADA?

Several team managers urged the World Anti-Doping Agency (WADA) to seize the issue. "The guarantor of the fairness of the sport must react very quickly, it is harmful," Vincent Lavenu, boss of the AG2R-La Mondiale team, said on Wednesday.

For the moment, however, ketones are not a product banned by WADA, which requires that two of the following three criteria be met to ban a substance: it must improve performance, pose a risk to health and / or to be unethical. This is not the case, AMA told AFP on Wednesday.

"Several studies have shown that ketones have no effect on performance," she said.

WADA has, however, indicated its "concern" with the "production and labeling of food supplements" that may lead to the presence, voluntary or not, of "banned substances" within them.

© 2019 AFP