The actor was spotted filming his upcoming Netflix series Maniac, looking slimmer than ever before in his office attire on set.
The actor, who is known to have shrinked his size for roles including his part in Moneyball, most recently gained weight for his starring turn in 2016's War Dogs, in which he played arms dealer Efraim Diveroli. Jonah is thought to have been at his heaviest weight ever during filming in 2015.
His health kick was first noticed during the 2017 awards season, though it was this photograph from June that sent the internet into meltdown.
After filming on War Dogs wrapped, the actor revealed that he called on his close friend Channing Tatum for help to drop the weight.
"I gained weight for this movie War Dogs," the actor told Jimmy Fallon in late 2016. "And then I wanted to get in better shape, so I called Channing Tatum, and said, 'Hey, if I ate less and go to a trainer, will I get in better shape?" And he said, 'Yes, you dumb motherf**ker, of course you will, it's the simplest thing in the entire world'."