Romain Grosjean jokingly suggested he might have overdone it on the weight gain over the winter break. Formula 1 has changed the weight restrictions meaning drivers have more freedom on diet plans.
Taller drivers are no longer disadvantaged from the new way in which the minimum car and driver weight is calculated. Any driver who weights under 80kg will have the ballast in the cockpit.
Grosjean, 32, joked about taking these new guidelines too seriously.
"Yeah, I may have overdone it! I've been 1m80cm and 69 kilos for like six or seven years, and I think now with the freedom I might have reached a bit more! So I'm going back on diet. It was good fun though," he told Autosport.
"But, it's great. It's much better in terms of health and fitness-wise as well. You can see that you're getting better and stronger and so on, but you still cannot be a bodybuilder.
"I've put quite a fair bit of muscles on. I just need to sweat off a little bit for the first race but we're going to be alright. I think the regulation is a good step in the right direction, and it's much nicer to live that way."
Meanwhile, Kevin Magnussen has also enjoyed his winter break. The other Haas driver claims he's put on weight, but nothing too drastic.
"I think I've gained muscle but we're talking maybe a kilo or two from where I finished last season. That's not something you would see massively. I don't expect anyone to come in and look like the [Incredible] Hulk," Magnussen added.
Haas revealed their 2019 livery last Thursday. Their full reveal will take place on the morning of the first test in Barcelona.