"Six months no beer," Pratt posted on Twitter over the weekend, adding: "My brother made me post this."
The selfie showed the amazing physical transformation he's undergoing for his part in the upcoming sci-fi movie, Guardians of the Galaxy, which he name-checked with the hash tag GOTG, and elicited a response from famous friends.
Pratt's Parks & Recreation costar Rob Lowe Tweeted: "You CANNOT return to Pawnee like that!"
Pratt is no stranger to yo-yo dieting. The actor, 33, who is a new dad and married to Anna Faris, got ripped for his role as a Navy Seal in Zero Dark Thirty.
Splash News Online
"Being in good physical shape is the best way to combat depression. You just have endorphins running around your body. It is the best anti-depressive that there is," he told PEOPLE earlier this year. Though he also admits: "There is really no room for vanity in comedy. Comedy comes from pain and it is a lot easier to empathize with somebody who is out of shape."
He wasn't shy a few summers ago in his tiny patriotic shorts, but fans might agree this new look is pretty easy on the eyes.