Jason Segel has revealed that he was "forced" to shed a few pounds for a recent movie role.

The actor stars in The Five-Year Engagement where he plays the fianc of Emily Blunt's character.

And the comedic star says that he was given the brutal news that he would have to shape up in order to truly pull off the part.

"I was forced to lose weight for this movie," Jason told David Letterman. "I was told that it had to be conceivable that Emily Blunt would ever choose me to be her husband. Which is fair."

Jason told the late night host that he had lost a "good 35 pounds" but found a way to cheat on his healthy eating programme.

"I didn't enjoy it," he grumbled. "But they sent a trainer to set and I had to work out twice a day and then he would watch me eat all day."

"What they didn't anticipate is that I'm very clever, Dave, and I play a chef in the movie. So there are a lot of scenes where I have to eat. I would pay my co-stars nominal amounts of money to mess up their lines during the scenes so I would get to keep eating."