Max Verstappen put on, and then lost again, an astonishing 10 kilograms over the winter break.
Observers at the Bahrain test noticed the back-to-back title winner looking particularly slim.
The 25-year-old Dutchman admitted he put on weight over Christmas, with De Telegraaf newspaper reporting that he then lost the entire 10 kilos in six weeks.
"All year round I feel like I’m under my normal weight," Verstappen said, explaining that his usual winter weight gain in other years is about 5kg.
"Then I give myself a month to eat and drink what I want and have a little fun."
The Red Bull driver, however, said he then has no problem losing the weight, joking: "I like to hurt myself a bit."
Verstappen has also revealed that he will use a motorhome at the European grands prix this year.
"It’s so I can stay focused during the race weekends," he said. "And I can maybe stay in bed a bit longer in the morning.
"But above all it’s about privacy," said the back-to-back drivers’ champion.
Verstappen, however, rejected Dr Helmut Marko’s claim that he is having a driver simulator built into his private jet.
"That’s a misunderstanding," he said. "It would be cool, but I don’t think there would be much room left."