The Tour de France is again embroiled in a debate over what cyclists put in their bodies after Dutch team Jumbo acknowledged they were using a dietary aid believed to boost stamina.
The team responded to questions from Dutch newspaper De Telegraaf by saying they were using drinks based on a substance called ketones, which occur naturally in the body.
Jumbo team manager Richard Plugge says the use of ketones is nothing unusual and is widespread among Tour de France riders.
"It's a food supplement, like vitamins," he told De Telegraaf.
Ketones are "supplementary fuel for the muscles," said Jean-Jacques Menuet, the doctor for a rival team, Arkea-Samsic.
Jumbo won four of the first 11 stages on this year's Tour de France.
Mike Teunissen won the opening stage before Jumbo romped to victory in the team time trial the next day. Dylan Groenewegen won stage six in a sprint and Wout Van Aert took stage 10 on Monday.
On the Tour's rest day on Tuesday, Ineos team principal Dave Brailsford described Jumbo as "the most improved team over the past three years."