The 33-year-old, who shot to fame for his appearance in Superbad in 2007, was unrecognisable appearing at the 23rd Annual Screen Actors Guild Awards in LA, California on January 29.
And this week he debuted an even slimmer figuere as he left a personal training session at the gym.
As well as making a name for himself for his comedic roles in other films such as Knocked Up, 21 and 22 Jump Street and Wolf of Wall Street, Jonah has spoken publically in the past about his fluctuating size.
He's revealed he was thin in high school but gained weight as an adult jonah hill weight loss diet
I gained weight for this movie War Dogs, and then I wanted to get in better shape, so I called Channing Tatum, and said, ‘Hey, if I eat less and go to a trainer, will I get in better shape?